aboutsummaryrefslogtreecommitdiff
path: root/common/system.h
blob: 405d6a90a83d0c3da2f71df24b6abedbb3970178 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */

#ifndef COMMON_SYSTEM_H
#define COMMON_SYSTEM_H

#include "common/scummsys.h"
#include "common/noncopyable.h"
#include "common/list.h" // For OSystem::getSupportedFormats()
#include "graphics/pixelformat.h"
#include "graphics/mode.h"

namespace Audio {
class Mixer;
}

namespace Graphics {
struct Surface;
}

namespace Common {
class EventManager;
struct Rect;
class SaveFileManager;
class SearchSet;
class String;
#if defined(USE_TASKBAR)
class TaskbarManager;
#endif
#if defined(USE_UPDATES)
class UpdateManager;
#endif
class TimerManager;
class SeekableReadStream;
class WriteStream;
#ifdef ENABLE_KEYMAPPER
class HardwareInputSet;
class Keymap;
class KeymapperDefaultBindings;
#endif
}

class AudioCDManager;
class FilesystemFactory;
class PaletteManager;

/**
 * A structure describing time and date. This is a clone of struct tm
 * from time.h. We roll our own since not all systems provide time.h.
 * We also do not imitate all files of struct tm, only those we
 * actually need.
 *
 * @note For now, the members are named exactly as in struct tm to ease
 * the transition.
 */
struct TimeDate {
	int tm_sec;     ///< seconds (0 - 60)
	int tm_min;     ///< minutes (0 - 59)
	int tm_hour;    ///< hours (0 - 23)
	int tm_mday;    ///< day of month (1 - 31)
	int tm_mon;     ///< month of year (0 - 11)
	int tm_year;    ///< year - 1900
	int tm_wday;    ///< days since Sunday (0 - 6)
};

namespace LogMessageType {

enum Type {
	kInfo,
	kError,
	kWarning,
	kDebug
};

} // End of namespace LogMessageType

/**
 * Interface for ScummVM backends. If you want to port ScummVM to a system
 * which is not currently covered by any of our backends, this is the place
 * to start. ScummVM will create an instance of a subclass of this interface
 * and use it to interact with the system.
 *
 * In particular, a backend provides a video surface for ScummVM to draw in;
 * methods to create timers, to handle user input events,
 * control audio CD playback, and sound output.
 */
class OSystem : Common::NonCopyable {
protected:
	OSystem();
	virtual ~OSystem();

protected:
	/**
	 * @name Module slots
	 *
	 * For backend authors only, the following pointers (= "slots) to various
	 * subsystem managers / factories / etc. can and should be set to
	 * a suitable instance of the respective type.
	 *
	 * For some of the slots, a default instance is set if your backend
	 * does not do so. For details, please look at the documentation of
	 * each slot.
	 *
	 * A backend may setup slot values in its initBackend() method,
	 * its constructor or somewhere in between. But it must a slot's value
	 * no later than in its initBackend() implementation, because
	 * OSystem::initBackend() will create any default instances if
	 * none has been set yet (and for other slots, will verify that
	 * one has been set; if not, an error may be generated).
	 */
	//@{

	/**
	 * No default value is provided for _audiocdManager by OSystem.
	 * However, BaseBackend::initBackend() does set a default value
	 * if none has been set before.
	 *
	 * @note _audiocdManager is deleted by the OSystem destructor.
	 */
	AudioCDManager *_audiocdManager;

	/**
	 * No default value is provided for _eventManager by OSystem.
	 * However, BaseBackend::initBackend() does set a default value
	 * if none has been set before.
	 *
	 * @note _eventManager is deleted by the OSystem destructor.
	 */
	Common::EventManager *_eventManager;

	/**
	 * No default value is provided for _timerManager by OSystem.
	 *
	 * @note _timerManager is deleted by the OSystem destructor.
	 */
	Common::TimerManager *_timerManager;

	/**
	 * No default value is provided for _savefileManager by OSystem.
	 *
	 * @note _savefileManager is deleted by the OSystem destructor.
	 */
	Common::SaveFileManager *_savefileManager;

#if defined(USE_TASKBAR)
	/**
	 * No default value is provided for _taskbarManager by OSystem.
	 *
	 * @note _taskbarManager is deleted by the OSystem destructor.
	 */
	Common::TaskbarManager *_taskbarManager;
#endif

#if defined(USE_UPDATES)
	/**
	 * No default value is provided for _updateManager by OSystem.
	 *
	 * @note _updateManager is deleted by the OSystem destructor.
	 */
	Common::UpdateManager *_updateManager;
#endif

	/**
	 * No default value is provided for _fsFactory by OSystem.
	 *
	 * Note that _fsFactory is typically required very early on,
	 * so it usually should be set in the backends constructor or shortly
	 * thereafter, and before initBackend() is called.
	 *
	 * @note _fsFactory is deleted by the OSystem destructor.
	 */
	FilesystemFactory *_fsFactory;

private:
	/**
	 * Indicate if initBackend() has been called.
	 */
	bool _backendInitialized;

	//@}

public:

	/**
	 *
	 * Destoy this OSystem instance.
	 */
	void destroy();

	/**
	 * The following method is called once, from main.cpp, after all
	 * config data (including command line params etc.) are fully loaded.
	 *
	 * @note Subclasses should always invoke the implementation of their
	 *       parent class. They should do so near the end of their own
	 *       implementation.
	 */
	virtual void initBackend();

	/**
	 * Return false if initBackend() has not yet been called and true otherwise.
	 * Some functionalities such as mutexes cannot be used until the backend
	 * is initialized.
	 */
	bool backendInitialized() const { return _backendInitialized; }

	/**
	 * Allows the backend to perform engine specific init.
	 * Called just before the engine is run.
	 */
	virtual void engineInit() { }

	/**
	 * Allows the backend to perform engine specific de-init.
	 * Called after the engine finishes.
	 */
	virtual void engineDone() { }

	/** @name Feature flags */
	//@{

	/**
	 * A feature in this context means an ability of the backend which can be
	 * either on or off. Examples include:
	 *  - fullscreen mode
	 *  - aspect ration correction
	 *  - a virtual keyboard for text entry (on PDAs)
	 *
	 * One has to distinguish between the *availability* of a feature,
	 * which can be checked using hasFeature(), and its *state*.
	 * For example, the SDL backend *has* the kFeatureFullscreenMode,
	 * so hasFeature returns true for it. On the other hand,
	 * fullscreen mode may be active or not; this can be determined
	 * by checking the state via getFeatureState(). Finally, to
	 * switch between fullscreen and windowed mode, use setFeatureState().
	 */
	enum Feature {
		/**
		 * If supported, this feature flag can be used to switch between
		 * windowed and fullscreen mode.
		 */
		kFeatureFullscreenMode,

		/**
		 * Control aspect ratio correction. Aspect ratio correction is used to
		 * correct games running at 320x200 (i.e with an aspect ratio of 8:5),
		 * but which on their original hardware were displayed with the
		 * standard 4:3 ratio (that is, the original graphics used non-square
		 * pixels). When the backend support this, then games running at
		 * 320x200 pixels should be scaled up to 320x240 pixels. For all other
		 * resolutions, ignore this feature flag.
		 * @note Backend implementors can find utility functions in common/scaler.h
		 *       which can be used to implement aspect ratio correction. In
		 *       stretch200To240() can stretch a rect, including (very fast)
		 *       particular, interpolation, and works in-place.
		 */
		kFeatureAspectRatioCorrection,

		/**
		 * If supported this flag can be used to switch between unfiltered and
		 * filtered graphics modes.
		 */
		kFeatureFilteringMode,

		/**
		 * Indicate if stretch modes are supported by the backend.
		 */
		kFeatureStretchMode,

		/**
		 * Determine whether a virtual keyboard is too be shown or not.
		 * This would mostly be implemented by backends for hand held devices,
		 * like PocketPC, Palms, Symbian phones like the P800, Zaurus, etc.
		 */
		kFeatureVirtualKeyboard,

		/**
		 * Backends supporting this feature allow specifying a custom palette
		 * for the cursor. The custom palette is used if the feature state
		 * is set to true by the client code via setFeatureState().
		 *
		 * It is currently used only by some Macintosh versions of Humongous
		 * Entertainment games. If the backend doesn't implement this feature
		 * then the engine switches to b/w versions of cursors.
		 * The GUI also relies on this feature for mouse cursors.
		 */
		kFeatureCursorPalette,

		/**
		 * A backend have this feature if its overlay pixel format has an alpha
		 * channel which offers at least 3-4 bits of accuracy (as opposed to
		 * just a single alpha bit).
		 *
		 * This feature has no associated state.
		 */
		kFeatureOverlaySupportsAlpha,

		/**
		 * Client code can set the state of this feature to true in order to
		 * iconify the application window.
		 */
		kFeatureIconifyWindow,

		/**
		 * Setting the state of this feature to true tells the backend to disable
		 * all key filtering/mapping, in cases where it would be beneficial to do so.
		 * As an example case, this is used in the AGI engine's predictive dialog.
		 * When the dialog is displayed this feature is set so that backends with
		 * phone-like keypad temporarily unmap all user actions which leads to
		 * comfortable word entry. Conversely, when the dialog exits the feature
		 * is set to false.
		 *
		 * TODO: The word 'beneficial' above is very unclear. Beneficial to
		 * whom and for what??? Just giving an example is not enough.
		 *
		 * TODO: Fingolfin suggests that the way the feature is used can be
		 * generalized in this sense: Have a keyboard mapping feature, which the
		 * engine queries for to assign keys to actions ("Here's my default key
		 * map for these actions, what do you want them set to?").
		 */
		kFeatureDisableKeyFiltering,

		/**
		 * The presence of this feature indicates whether the displayLogFile()
		 * call is supported.
		 *
		 * This feature has no associated state.
		 */
		kFeatureDisplayLogFile,

		/**
		 * The presence of this feature indicates whether the hasTextInClipboard(),
		 * getTextFromClipboard() and setTextInClipboard() calls are supported.
		 *
		 * This feature has no associated state.
		 */
		kFeatureClipboardSupport,

		/**
		 * The presence of this feature indicates whether the openUrl()
		 * call is supported.
		 *
		 * This feature has no associated state.
		 */
		kFeatureOpenUrl	,

		/**
		* show on-screen control
		*/
		kFeatureOnScreenControl,

		/**
		* mouse emulation mode
		*/
		kFeatureTouchpadMode,

		/**
		* swap menu and back buttons
		*/
		kFeatureSwapMenuAndBackButtons,

		/**
		* keyboard mouse and joystick mouse speed
		*/
		kFeatureKbdMouseSpeed,

		/**
		* change analog joystick deadzone
		*/
		kFeatureJoystickDeadzone,

		/**
		* shaders
		*/
		kFeatureShader

	};

	/**
	 * Determine whether the backend supports the specified feature.
	 */
	virtual bool hasFeature(Feature f) { return false; }

	/**
	 * En-/disable the specified feature. For example, this may be used to
	 * enable fullscreen mode, or to deactivate aspect correction, etc.
	 */
	virtual void setFeatureState(Feature f, bool enable) {}

	/**
	 * Query the state of the specified feature. For example, test whether
	 * fullscreen mode is active or not.
	 */
	virtual bool getFeatureState(Feature f) { return false; }

	//@}



	/**
	 * @name Graphics
	 *
	 * The way graphics work in the class OSystem are meant to make
	 * it possible for game frontends to implement all they need in
	 * an efficient manner. The downside of this is that it may be
	 * rather complicated for backend authors to fully understand and
	 * implement the semantics of the OSystem interface.
	 *
	 *
	 * The graphics visible to the user in the end are actually
	 * composed in three layers: the game graphics, the overlay
	 * graphics, and the mouse.
	 *
	 * First, there are the game graphics. The methods in this section
	 * deal with them exclusively. In particular, the size of the game
	 * graphics is defined by a call to initSize(), and
	 * copyRectToScreen() blits the data in the current pixel format
	 * into the game layer. Let W and H denote the width and height of
	 * the game graphics.
	 *
	 * Before the user sees these graphics, the backend may apply some
	 * transformations to it; for example, the may be scaled to better
	 * fit on the visible screen; or aspect ratio correction may be
	 * performed (see kFeatureAspectRatioCorrection). As a result of
	 * this, a pixel of the game graphics may occupy a region bigger
	 * than a single pixel on the screen. We define p_w and p_h to be
	 * the width resp. height of a game pixel on the screen.
	 *
	 * In addition, there is a vertical "shake offset" (as defined by
	 * setShakePos) which is used in some games to provide a shaking
	 * effect. Note that shaking is applied to all three layers, i.e.
	 * also to the overlay and the mouse. We denote the shake offset
	 * by S.
	 *
	 * Putting this together, a pixel (x,y) of the game graphics is
	 * transformed to a rectangle of height p_h and width p_w
	 * appearing at position (p_w * x, p_hw * (y + S)) on the real
	 * screen (in addition, a backend may choose to offset
	 * everything, e.g. to center the graphics on the screen).
	 *
	 *
	 * The next layer is the overlay. It is composed over the game
	 * graphics. Historically the overlay size had always been a
	 * multiple of the game resolution, for example when the game
	 * resolution was 320x200 and the user selected a 2x scaler and did
	 * not enable aspect ratio correction it had a size of 640x400.
	 * An exception was the aspect ratio correction, which did allow
	 * for non multiples of the vertical resolution of the game screen.
	 * Nowadays the overlay size does not need to have any relation to
	 * the game resolution though, for example the overlay resolution
	 * might be the same as the physical screen resolution.
	 * The overlay is forced to a 16bpp mode right now.
	 *
	 * Finally, there is the mouse layer. This layer doesn't have to
	 * actually exist within the backend -- it all depends on how a
	 * backend chooses to implement mouse cursors, but in the default
	 * SDL backend, it really is a separate layer. The mouse can
	 * have a palette of its own, if the backend supports it.
	 *
	 * On a note for OSystem users here. We do not require our graphics
	 * to be thread safe and in fact most/all backends using OpenGL are
	 * not. So do *not* try to call any of these functions from a timer
	 * and/or audio callback (like readBuffer of AudioStreams).
	 */
	//@{

	/**
	 * Description of a graphics mode.
	 */
	struct GraphicsMode {
		/**
		 * The 'name' of the graphics mode. This name is matched when selecting
		 * a mode via the command line, or via the config file.
		 * Examples: "1x", "advmame2x", "hq3x"
		 */
		const char *name;
		/**
		 * Human readable description of the scaler.
		 * Examples: "Normal (no scaling)", "AdvMAME2x", "HQ3x"
		 */
		const char *description;
		/**
		 * ID of the graphics mode. How to use this is completely up to the
		 * backend. This value will be passed to the setGraphicsMode(int)
		 * method by client code.
		 */
		int id;
	};

	/**
	 * Retrieve a list of all graphics modes supported by this backend.
	 * This can be both video modes as well as graphic filters/scalers;
	 * it is completely up to the backend maintainer to decide what is
	 * appropriate here and what not.
	 * The list is terminated by an all-zero entry.
	 * @return a list of supported graphics modes
	 */
	virtual const GraphicsMode *getSupportedGraphicsModes() const = 0;

	/**
	 * Return the ID of the 'default' graphics mode. What exactly this means
	 * is up to the backend. This mode is set by the client code when no user
	 * overrides are present (i.e. if no custom graphics mode is selected via
	 * the command line or a config file).
	 *
	 * @return the ID of the 'default' graphics mode
	 */
	virtual int getDefaultGraphicsMode() const = 0;

	/**
	 * Switch to the specified graphics mode. If switching to the new mode
	 * failed, this method returns false.
	 *
	 * @param mode	the ID of the new graphics mode
	 * @return true if the switch was successful, false otherwise
	 */
	virtual bool setGraphicsMode(int mode) = 0;

	/**
	 * Switch to the graphics mode with the given name. If 'name' is unknown,
	 * or if switching to the new mode failed, this method returns false.
	 *
	 * @param name	the name of the new graphics mode
	 * @return true if the switch was successful, false otherwise
	 * @note This is implemented via the setGraphicsMode(int) method, as well
	 *       as getSupportedGraphicsModes() and getDefaultGraphicsMode().
	 *       In particular, backends do not have to overload this!
	 */
	bool setGraphicsMode(const char *name);

	/**
	 * Determine which graphics mode is currently active.
	 * @return the ID of the active graphics mode
	 */
	virtual int getGraphicsMode() const = 0;

	/**
	 * Sets the graphics scale factor to x1. Games with large screen sizes
	 * reset the scale to x1 so the screen will not be too big when starting
	 * the game.
	 */
	virtual void resetGraphicsScale() {}

#ifdef USE_RGB_COLOR
	/**
	 * Determine the pixel format currently in use for screen rendering.
	 * @return the active screen pixel format.
	 * @see Graphics::PixelFormat
	 */
	virtual Graphics::PixelFormat getScreenFormat() const = 0;

	/**
	 * Returns a list of all pixel formats supported by the backend.
	 * The first item in the list must be directly supported by hardware,
	 * and provide the largest color space of those formats with direct
	 * hardware support. It is also strongly recommended that remaining
	 * formats should be placed in order of descending preference for the
	 * backend to use.
	 *
	 * EG: a backend that supports 32-bit ABGR and 16-bit 555 BGR in hardware
	 * and provides conversion from equivalent RGB(A) modes should order its list
	 *    1) Graphics::PixelFormat(4, 0, 0, 0, 0, 0, 8, 16, 24)
	 *    2) Graphics::PixelFormat(2, 3, 3, 3, 8, 0, 5, 10, 0)
	 *    3) Graphics::PixelFormat(4, 0, 0, 0, 0, 24, 16, 8, 0)
	 *    4) Graphics::PixelFormat(2, 3, 3, 3, 8, 10, 5, 0, 0)
	 *    5) Graphics::PixelFormat::createFormatCLUT8()
	 *
	 * @see Graphics::PixelFormat
	 *
	 * @note Backends supporting RGB color should accept game data in RGB color
	 *       order, even if hardware uses BGR or some other color order.
	 */
	virtual Common::List<Graphics::PixelFormat> getSupportedFormats() const = 0;
#else
	inline Graphics::PixelFormat getScreenFormat() const {
		return Graphics::PixelFormat::createFormatCLUT8();
	};

	inline Common::List<Graphics::PixelFormat> getSupportedFormats() const {
		Common::List<Graphics::PixelFormat> list;
		list.push_back(Graphics::PixelFormat::createFormatCLUT8());
		return list;
	};
#endif

	/**
	 * Retrieve a list of all hardware shaders supported by this backend.
	 * This can be only hardware shaders.
	 * it is completely up to the backend maintainer to decide what is
	 * appropriate here and what not.
	 * The list is terminated by an all-zero entry.
	 * @return a list of supported shaders
	 */
	virtual const GraphicsMode *getSupportedShaders() const {
		static const OSystem::GraphicsMode no_shader[2] = {{"NONE", "Normal (no shader)", 0}, {nullptr, nullptr, 0}};
		return no_shader;
	}

	/**
	 * Switch to the specified shader mode. If switching to the new mode
	 * failed, this method returns false.
	 *
	 * @param mode	the ID of the new shader mode
	 * @return true if the switch was successful, false otherwise
	 */
	virtual bool setShader(int id) { return false; }

	/**
	 * Determine which shader is currently active.
	 * @return the ID of the active shader
	 */
	virtual int getShader() const { return 0; }

	/**
	 * Retrieve a list of all stretch modes supported by this backend.
	 * It is completely up to the backend maintainer to decide what is
	 * appropriate here and what not.
	 * The list is terminated by an all-zero entry.
	 * @return a list of supported stretch modes
	 */
	virtual const GraphicsMode *getSupportedStretchModes() const {
		static const GraphicsMode noStretchModes[] = {{"NONE", "Normal", 0}, {nullptr, nullptr, 0 }};
		return noStretchModes;
	}

	/**
	 * Return the ID of the 'default' stretch mode. What exactly this means
	 * is up to the backend. This mode is set by the client code when no user
	 * overrides are present (i.e. if no custom stretch mode is selected via
	 * the command line or a config file).
	 *
	 * @return the ID of the 'default' graphics mode
	 */
	virtual int getDefaultStretchMode() const { return 0; }

	/**
	 * Switch to the specified stretch mode. If switching to the new mode
	 * failed, this method returns false.
	 *
	 * @param mode	the ID of the new graphics mode
	 * @return true if the switch was successful, false otherwise
	 */
	virtual bool setStretchMode(int mode) { return false; }

	/**
	 * Switch to the stretch mode with the given name. If 'name' is unknown,
	 * or if switching to the new mode failed, this method returns false.
	 *
	 * @param name	the name of the new stretch mode
	 * @return true if the switch was successful, false otherwise
	 * @note This is implemented via the setStretchMode(int) method, as well
	 *       as getSupportedStretchModes() and getDefaultStretchMode().
	 *       In particular, backends do not have to overload this!
	 */
	bool setStretchMode(const char *name);

	/**
	 * Determine which stretch mode is currently active.
	 * @return the ID of the active stretch mode
	 */
	virtual int getStretchMode() const { return 0; }


	/**
	 * Set the size and color format of the virtual screen. Typical sizes include:
	 *  - 320x200 (e.g. for most SCUMM games, and Simon)
	 *  - 320x240 (e.g. for FM-TOWN SCUMM games)
	 *  - 640x480 (e.g. for Curse of Monkey Island)
	 *
	 * This is the resolution for which the client code generates data;
	 * this is not necessarily equal to the actual display size. For example,
	 * a backend may magnify the graphics to fit on screen (see also the
	 * GraphicsMode); stretch the data to perform aspect ratio correction;
	 * or shrink it to fit on small screens (in cell phones).
	 *
	 * Typical formats include:
	 *  CLUT8 (e.g. 256 color, for most games)
	 *  RGB555 (e.g. 16-bit color, for later SCUMM HE games)
	 *  RGB565 (e.g. 16-bit color, for Urban Runner)
	 *
	 * This is the pixel format for which the client code generates data;
	 * this is not necessarily equal to the hardware pixel format. For example,
	 * a backend may perform color lookup of 8-bit graphics before pushing
	 * a screen to hardware, or correct the ARGB color order.
	 *
	 * @param width		the new virtual screen width
	 * @param height	the new virtual screen height
	 * @param format	the new virtual screen pixel format
	 */
	virtual void initSize(uint width, uint height, const Graphics::PixelFormat *format = nullptr) = 0;

	/**
	 * Send a list of graphics modes to the backend so it can make a decision
	 * about the best way to set up the display hardware.
	 *
	 * Engines that switch between different virtual screen sizes during a game
	 * should call this function prior to any call to initSize. Engines that use
	 * only a single screen size do not need to call this function.
	 *
	 * @param modes the list of graphics modes the engine will probably use.
	 */
	virtual void initSizeHint(const Graphics::ModeList &modes) {}

	/**
	 * Return an int value which is changed whenever any screen
	 * parameters (like the resolution) change. That is, whenever a
	 * EVENT_SCREEN_CHANGED would be sent. You can track this value
	 * in your code to detect screen changes in case you do not have
	 * full control over the event loop(s) being used (like the GUI
	 * code).
	 *
	 * @return an integer which can be used to track screen changes
	 *
	 * @note Backends which generate EVENT_SCREEN_CHANGED events MUST
	 *       overload this method appropriately.
	 */
	virtual int getScreenChangeID() const { return 0; }

	/**
	 * Begin a new GFX transaction, which is a sequence of GFX mode changes.
	 * The idea behind GFX transactions is to make it possible to activate
	 * several different GFX changes at once as a "batch" operation. For
	 * example, assume we are running in 320x200 with a 2x scaler (thus using
	 * 640x400 pixels in total). Now, we want to switch to 640x400 with the 1x
	 * scaler. Without transactions, we have to choose whether we want to first
	 * switch the scaler mode, or first to 640x400 mode. In either case,
	 * depending on the backend implementation, some ugliness may result.
	 * E.g. the window might briefly switch to 320x200 or 1280x800.
	 * Using transactions, this can be avoided.
	 *
	 * @note Transaction support is optional, and the default implementations
	 *       of the relevant methods simply do nothing.
	 * @see endGFXTransaction
	 */
	virtual void beginGFXTransaction() {}

	/**
	 * This type is able to save the different errors which can happen while
	 * changing GFX config values inside GFX transactions.
	 *
	 * endGFXTransaction returns a ORed combination of the '*Failed' values
	 * if any problem occures, on success 0.
	 *
	 * @see endGFXTransaction
	 */
	enum TransactionError {
		kTransactionSuccess = 0,					/**< Everything fine (use EQUAL check for this one!) */
		kTransactionAspectRatioFailed = (1 << 0),	/**< Failed switching aspect ratio correction mode */
		kTransactionFullscreenFailed = (1 << 1),	/**< Failed switching fullscreen mode */
		kTransactionModeSwitchFailed = (1 << 2),	/**< Failed switching the GFX graphics mode (setGraphicsMode) */
		kTransactionSizeChangeFailed = (1 << 3),	/**< Failed switching the screen dimensions (initSize) */
		kTransactionFormatNotSupported = (1 << 4),	/**< Failed setting the color format */
		kTransactionFilteringFailed = (1 << 5),		/**< Failed setting the filtering mode */
		kTransactionStretchModeSwitchFailed = (1 << 6)	/**< Failed setting the stretch mode */
	};

	/**
	 * End (and thereby commit) the current GFX transaction.
	 * @see beginGFXTransaction
	 * @see kTransactionError
	 * @return returns a ORed combination of TransactionError values or 0 on success
	 */
	virtual TransactionError endGFXTransaction() { return kTransactionSuccess; }


	/**
	 * Returns the currently set virtual screen height.
	 * @see initSize
	 * @return the currently set virtual screen height
	 */
	virtual int16 getHeight() = 0;

	/**
	 * Returns the currently set virtual screen width.
	 * @see initSize
	 * @return the currently set virtual screen width
	 */
	virtual int16 getWidth() = 0;

	/**
	 * Return the palette manager singleton. For more information, refer
	 * to the PaletteManager documentation.
	 */
	virtual PaletteManager *getPaletteManager() = 0;

	/**
	 * Blit a bitmap to the virtual screen.
	 * The real screen will not immediately be updated to reflect the changes.
	 * Client code has to to call updateScreen to ensure any changes are
	 * visible to the user. This can be used to optimize drawing and reduce
	 * flicker.
	 * If the current pixel format has one byte per pixel, the graphics data
	 * uses 8 bits per pixel, using the palette specified via setPalette.
	 * If more than one byte per pixel is in use, the graphics data uses the
	 * pixel format returned by getScreenFormat.
	 *
	 * @param buf		the buffer containing the graphics data source
	 * @param pitch		the pitch of the buffer (number of bytes in a scanline)
	 * @param x			the x coordinate of the destination rectangle
	 * @param y			the y coordinate of the destination rectangle
	 * @param w			the width of the destination rectangle
	 * @param h			the height of the destination rectangle
	 *
	 * @note The specified destination rectangle must be completly contained
	 *       in the visible screen space, and must be non-empty. If not, a
	 *       backend may or may not perform clipping, trigger an assert or
	 *       silently corrupt memory.
	 *
	 * @see updateScreen
	 * @see getScreenFormat
	 */
	virtual void copyRectToScreen(const void *buf, int pitch, int x, int y, int w, int h) = 0;

	/**
	 * Lock the active screen framebuffer and return a Graphics::Surface
	 * representing it. The caller can then perform arbitrary graphics
	 * transformations on the framebuffer (blitting, scrolling, etc.).
	 * Must be followed by matching call to unlockScreen(). Calling code
	 * should make sure to only lock the framebuffer for the briefest
	 * periods of time possible, as the whole system is potentially stalled
	 * while the lock is active.
	 * Returns 0 if an error occurred. Otherwise a surface with the pixel
	 * format described by getScreenFormat is returned.
	 *
	 * The returned surface must *not* be deleted by the client code.
	 *
	 * @see getScreenFormat
	 */
	virtual Graphics::Surface *lockScreen() = 0;

	/**
	 * Unlock the screen framebuffer, and mark it as dirty (i.e. during the
	 * next updateScreen() call, the whole screen will be updated.
	 */
	virtual void unlockScreen() = 0;

	/**
	 * Fills the screen with a given color value.
	 *
	 * @note We are using uint32 here even though currently
	 * we only support 8bpp indexed mode. Thus the value should
	 * be always inside [0, 255] for now.
	 */
	virtual void fillScreen(uint32 col) = 0;

	/**
	 * Flush the whole screen, that is render the current content of the screen
	 * framebuffer to the display.
	 *
	 * This method could be called very often by engines. Backends are hence
	 * supposed to only perform any redrawing if it is necessary, and otherwise
	 * return immediately. See
	 * <http://wiki.scummvm.org/index.php/HOWTO-Backends#updateScreen.28.29_method>
	 */
	virtual void updateScreen() = 0;

	/**
	 * Set current shake position, a feature needed for some SCUMM screen
	 * effects. The effect causes the displayed graphics to be shifted upwards
	 * by the specified (always positive) offset. The area at the bottom of the
	 * screen which is moved into view by this is filled with black. This does
	 * not cause any graphic data to be lost - that is, to restore the original
	 * view, the game engine only has to call this method again with offset
	 * equal to zero. No calls to copyRectToScreen are necessary.
	 * @param shakeOffset	the shake offset
	 *
	 * @note This is currently used in the SCUMM, QUEEN and KYRA engines.
	 */
	virtual void setShakePos(int shakeOffset) = 0;

	/**
	 * Sets the area of the screen that has the focus.  For example, when a character
	 * is speaking, they will have the focus.  Allows for pan-and-scan style views
	 * where the backend could follow the speaking character or area of interest on
	 * the screen.
	 *
	 * The backend is responsible for clipping the rectangle and deciding how best to
	 * zoom the screen to show any shape and size rectangle the engine provides.
	 *
	 * @param rect A rectangle on the screen to be focused on
	 * @see clearFocusRectangle
	 */
	virtual void setFocusRectangle(const Common::Rect& rect) {}

	/**
	 * Clears the focus set by a call to setFocusRectangle().  This allows the engine
	 * to clear the focus during times when no particular area of the screen has the
	 * focus.
	 * @see setFocusRectangle
	 */
	virtual void clearFocusRectangle() {}

	//@}



	/**
	 * @name Overlay
	 * In order to be able to display dialogs atop the game graphics, backends
	 * must provide an overlay mode.
	 *
	 * The overlay is currently forced at 16 bpp.
	 *
	 * For 'coolness' we usually want to have an overlay which is blended over
	 * the game graphics. On backends which support alpha blending, this is
	 * no issue; but on other systems this needs some trickery.
	 *
	 * Essentially, we fake (alpha) blending on these systems by copying the
	 * current game graphics into the overlay buffer when activating the overlay,
	 * then manually compose whatever graphics we want to show in the overlay.
	 * This works because we assume the game to be "paused" whenever an overlay
	 * is active.
	 */
	//@{

	/** Activate the overlay mode. */
	virtual void showOverlay() = 0;

	/** Deactivate the overlay mode. */
	virtual void hideOverlay() = 0;

	/**
	 * Returns the pixel format description of the overlay.
	 * @see Graphics::PixelFormat
	 */
	virtual Graphics::PixelFormat getOverlayFormat() const = 0;

	/**
	 * Reset the overlay.
	 *
	 * After calling this method while the overlay mode is active, the user
	 * should be seeing only the game graphics. How this is achieved depends
	 * on how the backend implements the overlay. Either it sets all pixels of
	 * the overlay to be transparent (when alpha blending is used).
	 *
	 * Or, in case of fake alpha blending, it might just put a copy of the
	 * current game graphics screen into the overlay.
	 */
	virtual void clearOverlay() = 0;

	/**
	 * Copy the content of the overlay into a buffer provided by the caller.
	 * This is only used to implement fake alpha blending.
	 */
	virtual void grabOverlay(void *buf, int pitch) = 0;

	/**
	 * Blit a graphics buffer to the overlay.
	 * In a sense, this is the reverse of grabOverlay.
	 *
	 * @param buf		the buffer containing the graphics data source
	 * @param pitch		the pitch of the buffer (number of bytes in a scanline)
	 * @param x			the x coordinate of the destination rectangle
	 * @param y			the y coordinate of the destination rectangle
	 * @param w			the width of the destination rectangle
	 * @param h			the height of the destination rectangle
	 *
	 * @see copyRectToScreen
	 * @see grabOverlay
	 */
	virtual void copyRectToOverlay(const void *buf, int pitch, int x, int y, int w, int h) = 0;

	/**
	 * Return the height of the overlay.
	 * @see getHeight
	 */
	virtual int16 getOverlayHeight() = 0;

	/**
	 * Return the width of the overlay.
	 * @see getWidth
	 */
	virtual int16 getOverlayWidth() = 0;

	//@}



	/** @name Mouse
	 * This is the lower level implementation as provided by the
	 * backends. The engines should use the Graphics::CursorManager
	 * class instead of using it directly.
	 */
	//@{

	/**
	 * Show or hide the mouse cursor.
	 *
	 * Currently the backend is not required to immediately draw the
	 * mouse cursor on showMouse(true).
	 *
	 * TODO: We might want to reconsider this fact,
	 * check Graphics::CursorManager::showMouse for some details about
	 * this.
	 *
	 * @see Graphics::CursorManager::showMouse
	 */
	virtual bool showMouse(bool visible) = 0;

	/**
	 * Move ("warp") the mouse cursor to the specified position in virtual
	 * screen coordinates.
	 * @param x		the new x position of the mouse
	 * @param y		the new y position of the mouse
	 */
	virtual void warpMouse(int x, int y) = 0;

	/**
	 * Set the bitmap used for drawing the cursor.
	 *
	 * @param buf				the pixmap data to be used
	 * @param w					width of the mouse cursor
	 * @param h					height of the mouse cursor
	 * @param hotspotX			horizontal offset from the left side to the hotspot
	 * @param hotspotY			vertical offset from the top side to the hotspot
	 * @param keycolor			transparency color value. This should not exceed the maximum color value of the specified format.
	 *                          In case it does the behavior is undefined. The backend might just error out or simply ignore the
	 *                          value. (The SDL backend will just assert to prevent abuse of this).
	 * @param dontScale			Whether the cursor should never be scaled. An exception are high ppi displays, where the cursor
	 *                          would be too small to notice otherwise, these are allowed to scale the cursor anyway.
	 * @param format			pointer to the pixel format which cursor graphic uses (0 means CLUT8)
	 */
	virtual void setMouseCursor(const void *buf, uint w, uint h, int hotspotX, int hotspotY, uint32 keycolor, bool dontScale = false, const Graphics::PixelFormat *format = nullptr) = 0;

	/**
	 * Replace the specified range of cursor the palette with new colors.
	 * The palette entries from 'start' till (start+num-1) will be replaced - so
	 * a full palette update is accomplished via start=0, num=256.
	 *
	 * Backends which implement it should have kFeatureCursorPalette flag set
	 *
	 * @see setPalette
	 * @see kFeatureCursorPalette
	 */
	virtual void setCursorPalette(const byte *colors, uint start, uint num) {}

	//@}



	/** @name Events and Time */
	//@{

	/** Get the number of milliseconds since the program was started.

	    @param skipRecord   Skip recording of this value by event recorder.
	    			This could be needed particularly when we are in
				an on-screen GUI loop where player can pause
				the recording.
	*/
	virtual uint32 getMillis(bool skipRecord = false) = 0;

	/** Delay/sleep for the specified amount of milliseconds. */
	virtual void delayMillis(uint msecs) = 0;

	/**
	 * Get the current time and date, in the local timezone.
	 * Corresponds on many systems to the combination of time()
	 * and localtime().
	 */
	virtual void getTimeAndDate(TimeDate &t) const = 0;

	/**
	 * Return the timer manager singleton. For more information, refer
	 * to the TimerManager documentation.
	 */
	virtual Common::TimerManager *getTimerManager();

	/**
	 * Return the event manager singleton. For more information, refer
	 * to the EventManager documentation.
	 */
	inline Common::EventManager *getEventManager() {
		return _eventManager;
	}

#ifdef ENABLE_KEYMAPPER
	/**
	 * Register hardware inputs with keymapper
	 * IMPORTANT NOTE: This is part of the WIP Keymapper. If you plan to use
	 * this, please talk to tsoliman and/or LordHoto.
	 *
	 * @return HardwareInputSet with all keys and recommended mappings
	 *
	 * See keymapper documentation for further reference.
	 */
	virtual Common::HardwareInputSet *getHardwareInputSet() { return nullptr; }

	/**
	 * Return a platform-specific global keymap
	 * IMPORTANT NOTE: This is part of the WIP Keymapper. If you plan to use
	 * this, please talk to tsoliman and/or LordHoto.
	 *
	 * @return Keymap with actions appropriate for the platform
	 *
	 * The caller will use and delete the return object.
	 *
	 * See keymapper documentation for further reference.
	 */
	virtual Common::Keymap *getGlobalKeymap() { return nullptr; }

	/**
	 * Return platform-specific default keybindings
	 * IMPORTANT NOTE: This is part of the WIP Keymapper. If you plan to use
	 * this, please talk to tsoliman and/or LordHoto.
	 *
	 * @return KeymapperDefaultBindings populated with keybindings
	 *
	 * See keymapper documentation for further reference.
	 */
	virtual Common::KeymapperDefaultBindings *getKeymapperDefaultBindings() { return nullptr; }
#endif
	//@}



	/**
	 * @name Mutex handling
	 * Historically, the OSystem API used to have a method which allowed
	 * creating threads. Hence mutex support was needed for thread syncing.
	 * To ease portability, though, we decided to remove the threading API.
	 * Instead, we now use timers (see setTimerCallback() and Common::Timer).
	 * But since those may be implemented using threads (and in fact, that's
	 * how our primary backend, the SDL one, does it on many systems), we
	 * still have to do mutex syncing in our timer callbacks.
	 * In addition, the sound mixer uses a mutex in case the backend runs it
	 * from a dedicated thread (as e.g. the SDL backend does).
	 *
	 * Hence backends which do not use threads to implement the timers simply
	 * can use dummy implementations for these methods.
	 */
	//@{

	typedef struct OpaqueMutex *MutexRef;

	/**
	 * Create a new mutex.
	 * @return the newly created mutex, or 0 if an error occurred.
	 */
	virtual MutexRef createMutex() = 0;

	/**
	 * Lock the given mutex.
	 *
	 * @note ScummVM code assumes that the mutex implementation supports
	 * recursive locking. That is, a thread may lock a mutex twice w/o
	 * deadlocking. In case of a multilock, the mutex has to be unlocked
	 * as many times as it was locked befored it really becomes unlocked.
	 *
	 * @param mutex	the mutex to lock.
	 */
	virtual void lockMutex(MutexRef mutex) = 0;

	/**
	 * Unlock the given mutex.
	 * @param mutex	the mutex to unlock.
	 */
	virtual void unlockMutex(MutexRef mutex) = 0;

	/**
	 * Delete the given mutex. Make sure the mutex is unlocked before you delete it.
	 * If you delete a locked mutex, the behavior is undefined, in particular, your
	 * program may crash.
	 * @param mutex	the mutex to delete.
	 */
	virtual void deleteMutex(MutexRef mutex) = 0;

	//@}



	/** @name Sound */
	//@{

	/**
	 * Return the audio mixer. For more information, refer to the
	 * Audio::Mixer documentation.
	 */
	virtual Audio::Mixer *getMixer() = 0;

	//@}



	/** @name Audio CD */
	//@{

	/**
	 * Return the audio cd manager. For more information, refer to the
	 * AudioCDManager documentation.
	 */
	inline AudioCDManager *getAudioCDManager() {
		return _audiocdManager;
	}

	//@}



	/** @name Miscellaneous */
	//@{
	/** Quit (exit) the application. */
	virtual void quit() = 0;

	/**
	 * Signals that a fatal error inside the client code has happened.
	 *
	 * This should quit the application.
	 */
	virtual void fatalError();

	/**
	 * Set a window caption or any other comparable status display to the
	 * given value. The caption must be a pure ISO LATIN 1 string. Passing a
	 * string with a different encoding may lead to unexpected behavior,
	 * even crashes.
	 *
	 * @param caption	the window caption to use, as an ISO LATIN 1 string
	 */
	virtual void setWindowCaption(const char *caption) {}

	/**
	 * Display a message in an 'on screen display'. That is, display it in a
	 * fashion where it is visible on or near the screen (e.g. in a transparent
	 * rectangle over the regular screen content; or in a message box beneath
	 * it; etc.).
	 *
	 * The message is expected to be provided in the current TranslationManager
	 * charset.
	 *
	 * @note There is a default implementation in BaseBackend which uses a
	 *       TimedMessageDialog to display the message. Hence implementing
	 *       this is optional.
	 *
	 * @param msg	the message to display on screen
	 */
	virtual void displayMessageOnOSD(const char *msg) = 0;

	/**
	 * Display an icon indicating background activity
	 *
	 * The icon is displayed in an 'on screen display'. It is visible above
	 * the regular screen content or near it.
	 *
	 * The caller keeps ownership of the icon. It is acceptable to free
	 * the surface just after the call.
	 *
	 * There is no preferred pixel format for the icon. The backend should
	 * convert its copy of the icon to an appropriate format.
	 *
	 * The caller must call this method again with a null pointer
	 * as a parameter to indicate the icon should no longer be displayed.
	 *
	 * @param icon the icon to display on screen
	 */
	virtual void displayActivityIconOnOSD(const Graphics::Surface *icon) = 0;

	/**
	 * Return the SaveFileManager, used to store and load savestates
	 * and other modifiable persistent game data. For more information,
	 * refer to the SaveFileManager documentation.
	 */
	virtual Common::SaveFileManager *getSavefileManager();

#if defined(USE_TASKBAR)
	/**
	 * Returns the TaskbarManager, used to handle progress bars,
	 * icon overlay, tasks and recent items list on the taskbar.
	 *
	 * @return the TaskbarManager for the current architecture
	 */
	virtual Common::TaskbarManager *getTaskbarManager() {
		return _taskbarManager;
	}
#endif

#if defined(USE_UPDATES)
	/**
	 * Returns the UpdateManager, used to handle auto-updating,
	 * and updating of ScummVM in general.
	 *
	 * @return the UpdateManager for the current architecture
	 */
	virtual Common::UpdateManager *getUpdateManager() {
		return _updateManager;
	}
#endif

	/**
	 * Returns the FilesystemFactory object, depending on the current architecture.
	 *
	 * @return the FSNode factory for the current architecture
	 */
	virtual FilesystemFactory *getFilesystemFactory();

	/**
	 * Add system specific Common::Archive objects to the given SearchSet.
	 * E.g. on Unix the dir corresponding to DATA_PATH (if set), or on
	 * Mac OS X the 'Resource' dir in the app bundle.
	 *
	 * @todo Come up with a better name. This one sucks.
	 *
	 * @param s		the SearchSet to which the system specific dirs, if any, are added
	 * @param priority	the priority with which those dirs are added
	 */
	virtual void addSysArchivesToSearchSet(Common::SearchSet &s, int priority = 0) {}

	/**
	 * Open the default config file for reading, by returning a suitable
	 * ReadStream instance. It is the callers responsiblity to delete
	 * the stream after use.
	 */
	virtual Common::SeekableReadStream *createConfigReadStream();

	/**
	 * Open the default config file for writing, by returning a suitable
	 * WriteStream instance. It is the callers responsiblity to delete
	 * the stream after use.
	 *
	 * May return 0 to indicate that writing to config file is not possible.
	 */
	virtual Common::WriteStream *createConfigWriteStream();

	/**
	 * Get the default file name (or even path) where the user configuration
	 * of ScummVM will be saved.
	 * Note that not all ports may use this.
	 */
	virtual Common::String getDefaultConfigFileName();

	/**
	 * Logs a given message.
	 *
	 * It is up to the backend where to log the different messages.
	 * The backend should aim at using a non-buffered output for it
	 * so that no log data is lost in case of a crash.
	 *
	 * The default implementation outputs them on stdout/stderr.
	 *
	 * @param type    the type of the message
	 * @param message the message itself
	 */
	virtual void logMessage(LogMessageType::Type type, const char *message) = 0;

	/**
	 * Open the log file in a way that allows the user to review it,
	 * and possibly email it (or parts of it) to the ScummVM team,
	 * e.g. as part of a bug report.
	 *
	 * On a desktop operating system, this would typically launch
	 * some kind of (external) text editor / viewer.
	 * On a phone, it might also cause a context switch to another
	 * application. Finally, on some ports, it might not be supported
	 * at all, and so do nothing.
	 *
	 * The kFeatureDisplayLogFile feature flag can be used to
	 * test whether this call has been implemented by the active
	 * backend.
	 *
	 * @return true if all seems to have gone fine, false if an error occurred
	 *
	 * @note An error could mean that the log file did not exist,
	 * or the editor could not launch. However, a return value of true does
	 * not guarantee that the user actually will see the log file.
	 *
	 * @note It is up to the backend to ensure that the system is in a state
	 * that allows the user to actually see the displayed log files. This
	 * might for example require leaving fullscreen mode.
	 */
	virtual bool displayLogFile() { return false; }

	/**
	 * Returns whether there is text available in the clipboard.
	 *
	 * The kFeatureClipboardSupport feature flag can be used to
	 * test whether this call has been implemented by the active
	 * backend.
	 *
	 * @return true if there is text in the clipboard, false otherwise
	 */
	virtual bool hasTextInClipboard() { return false; }

	/**
	 * Returns clipboard contents as a String.
	 *
	 * The kFeatureClipboardSupport feature flag can be used to
	 * test whether this call has been implemented by the active
	 * backend.
	 *
	 * @return clipboard contents ("" if hasTextInClipboard() == false)
	 */
	virtual Common::String getTextFromClipboard() { return ""; }

	/**
	 * Set the content of the clipboard to the given string.
	 *
	 * The kFeatureClipboardSupport feature flag can be used to
	 * test whether this call has been implemented by the active
	 * backend.
	 *
	 * @return true if the text was properly set in the clipboard, false otherwise
	 */
	virtual bool setTextInClipboard(const Common::String &text) { return false; }

	/**
	 * Open the given Url in the default browser (if available on the target
	 * system).
	 *
	 * @return true on success, false otherwise.
	 *
	 * @note It is up to the backend to ensure that the system is in a state
	 * that allows the user to actually see the web page. This might for
	 * example require leaving fullscreen mode.
	 *
	 * @parem url the URL to open
	 */
	virtual bool openUrl(const Common::String &url) {return false; }

	/**
	 * Returns the locale of the system.
	 *
	 * This returns the currently set up locale of the system, on which
	 * ScummVM is run.
	 *
	 * The format of the locale is language_country. These should match
	 * the POSIX locale values.
	 *
	 * For information about POSIX locales read here:
	 * http://en.wikipedia.org/wiki/Locale#POSIX-type_platforms
	 *
	 * The default implementation returns "en_US".
	 *
	 * @return locale of the system
	 */
	virtual Common::String getSystemLanguage() const;

	//@}
};


/** The global OSystem instance. Initialized in main(). */
extern OSystem *g_system;

#endif