aboutsummaryrefslogtreecommitdiff
path: root/common/system.h
blob: bd0caf457521d580d2767aaa06a6df1ecb4e4f88 (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
/* ScummVM - Scumm Interpreter
 * Copyright (C) 2001  Ludvig Strigeus
 * Copyright (C) 2001-2006 The ScummVM project
 *
 * 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.
 *
 * $URL$
 * $Id$
 *
 */

#ifndef COMMON_SYSTEM_H
#define COMMON_SYSTEM_H

#include "common/scummsys.h"
#include "common/mutex.h"
#include "common/rect.h"

namespace Audio {
	class Mixer;
}

namespace Graphics {
	struct Surface;
}

namespace Common {
	class SaveFileManager;
	class TimerManager;
}

/**
 * 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 {
private:
	// Prevent copying OSystem objects by accident.
	OSystem(const OSystem&);
	OSystem& operator= (const OSystem&);

protected:
	OSystem() { }
	virtual ~OSystem() { }

public:

	/**
	 * 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 so so near the end of their own
	 *       implementation.
	 */
	virtual void initBackend() { }

	/** @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)
	 */
	enum Feature {
		/**
		 * If your backend supports both a windowed and a fullscreen mode,
		 * then this feature flag can be used to switch between the two.
		 */
		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 You can find utility functions in common/scaler.h which can
		 *       be used to implement aspect ratio correction. In particular,
		 *       stretch200To240() can stretch a rect, including (very fast)
		 *       interpolation, and works in-place.
		 */
		kFeatureAspectRatioCorrection,

		/**
		 * 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,

		/**
		 * This flag is a bit more obscure: it gives a hint to the backend that
		 * the frontend code is very inefficient in doing screen updates. So
		 * the frontend might do a lot of fullscreen blits even though only a
		 * tiny portion of the actual screen data changed. In that case, it
		 * might pay off for the backend to compute which parts actual changed,
		 * and then only mark those as dirty.
		 * Implementing this is purely optional, and no harm should arise
		 * when not doing so (except for decreased speed in said frontends).
		 */
		kFeatureAutoComputeDirtyRects,

		/**
		 * This flags determines either cursor can have its own palette or not
		 * It is currently used only by some Macintosh versions of Humongous
		 * Entertainment games. If backend doesn't implement this feature then
		 * engine switches to b/w version of cursors.
		 */
		kFeatureCursorHasPalette,

		/**
		 * Set to true if the overlay pixel format has an alpha channel.
		 * This should only be set if it offers at least 3-4 bits of accuracy,
		 * as opposed to a single alpha bit.
		 */
		kFeatureOverlaySupportsAlpha,

		/**
		 * Set to true to iconify the window.
		 */
		kFeatureIconifyWindow
	};

	/**
	 * 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. They are always 8bpp, and
	 * 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 8bpp data into the
	 * game layer. Let W and H denote the width and height of the
	 * game graphics.
	 *
	 * Before the user sees these graphics, they may undergo certain
	 * transformations; 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 widht 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. By default, it has exactly the same size and
	 * resolution as the game graphics. However, client code can
	 * specify an overlay scale (as an additional parameter to
	 * initSize()). This is meant to increase the resolution of the
	 * overlay while keeping its size the same as that of the game
	 * graphics. For example, if the overlay scale is 2, and the game
	 * graphics have a resolution of 320x200; then the overlay shall
	 * have a resolution of 640x400, but it still has the same
	 * physical size as the game graphics.
	 *
	 *
	 * 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 is
	 * always in 8bpp but can have a palette of its own, if the
	 * backend supports it. The scale of the mouse cursor is called
	 * 'cursorTargetScale'. This is meant as a hint to the backend.
	 * For example, let us assume the overlay is not visible, and the
	 * game graphics are displayed using a 2x scaler. If a mouse
	 * cursor with a cursorTargetScale of 1 is set, then it should be
	 * scaled by factor 2x, too, just like the game graphics. But if
	 * it has a cursorTargetScale of 2, then it shouldn't be scaled
	 * again by the game graphics scaler.
	 */
	//@{

	/**
	 * 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 active graphics mode
	 */
	virtual int getGraphicsMode() const = 0;

	/**
	 * Set the size 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).
	 *
	 * @param width		the new virtual screen width
	 * @param height	the new virtual screen height
	 */
	virtual void initSize(uint width, uint height) = 0;

	/**
	 * 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() {};


	/**
	 * End (and thereby commit) the current GFX transaction.
	 * @see beginGFXTransaction
	 */
	virtual void endGFXTransaction() {};


	/**
	 * 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;

	/**
	 * Replace the specified range of 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.
	 *
	 * The palette data is specified in interleaved RGBA format. That is, the
	 * first byte of the memory block 'colors' points at is the red component
	 * of the first new color; the second byte the blue component of the first
	 * new color; the third byte the green component, the last byte to the alpha
	 * (transparency) value. Then the second color starts, and so on. So memory
	 * looks like this: R1-G1-B1-A1-R2-G2-B2-A2-R3-...
	 *
	 * @param colors	the new palette data, in interleaved RGB format
	 * @param start		the first palette entry to be updated
	 * @param num		the number of palette entries to be updated
	 *
	 * @note It is an error if start+num exceeds 256, behaviour is undefined
	 *       in that case (the backend may ignore it silently or assert).
	 * @note The alpha value is not actually used, and future revisions of this
	 *       API are probably going to remove it.
	 */
	virtual void setPalette(const byte *colors, uint start, uint num) = 0;

	/**
	 * Grabs a specified part of the currently active palette.
	 * The format is the same as for setPalette.
	 *
	 * @param colors	the palette data, in interleaved RGB format
	 * @param start		the first platte entry to be read
	 * @param num		the number of palette entries to be read
	 */
	virtual void grabPalette(byte *colors, uint start, uint num) = 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.
	 * The graphics data uses 8 bits per pixel, using the palette specified
	 * via setPalette.
	 *
	 * @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
	 */
	virtual void copyRectToScreen(const byte *buf, int pitch, int x, int y, int w, int h) = 0;

	/**
	 * Copies the current screen contents to a new surface, with the original
	 * bit depth. This will allocate memory for the pixel data.
	 * WARNING: surf->free() must be called by the user to avoid leaking.
	 *
	 * @param surf	the surfce to store the data in it
	 * @return true if all went well, false if an error occured
	 */
	virtual bool grabRawScreen(Graphics::Surface *surf) = 0;

	/**
	 * Clear the screen to black.
	 */
	virtual void clearScreen() {}

	/** Update the dirty areas of the screen. */
	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 by 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 a 0 offset. No calls to copyRectToScreen are necessary.
	 * @param shakeOffset	the shake offset
	 *
	 * @todo This is a rather special screen effect, only used by the SCUMM
	 *       frontend - we should consider removing it from the backend API
	 *       and instead implement the functionality in the frontend.
	 */
	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.
	 *
	 * While the game graphics are always 8 bpp, the overlay can be 8 or 16 bpp.
	 * Depending on which it is, OverlayColor is 8 or 16 bit.
	 *
	 * 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 (in particular those which only support
	 * 8bpp), this needs some trickery.
	 *
	 * Essentially, we fake (alpha) blending on these systems by copying the
	 * game graphics into the overlay buffer, then manually compose whatever
	 * graphics we want to show in the overlay.
	 */
	//@{

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

	/** Deactivate the overlay mode. */
	virtual void hideOverlay() = 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(OverlayColor *buf, int pitch) = 0;

	/**
	 * Blit a graphics buffer to the overlay.
	 * In a sense, this is the reverse of grabOverlay.
	 * @see copyRectToScreen
	 * @see grabOverlay
	 */
	virtual void copyRectToOverlay(const OverlayColor *buf, int pitch, int x, int y, int w, int h) = 0;

	/**
	 * Return the height of the overlay.
	 * @see getHeight
	 */
	virtual int16 getOverlayHeight()  { return getHeight(); }

	/**
	 * Return the width of the overlay.
	 * @see getWidth
	 */
	virtual int16 getOverlayWidth()   { return getWidth(); }

	virtual int screenToOverlayX(int x) { return x; }
	virtual int screenToOverlayY(int y) { return y; }
	virtual int overlayToScreenX(int x) { return x; }
	virtual int overlayToScreenY(int y) { return y; }

	/**
	* Convert the given RGB triplet into an OverlayColor. A OverlayColor can
	 * be 8bit, 16bit or 32bit, depending on the target system. The default
	 * implementation generates a 16 bit color value, in the 565 format
	 * (that is, 5 bits red, 6 bits green, 5 bits blue).
	 * @see colorToRGB
	 * @see ARGBToColor
	 */
	virtual OverlayColor RGBToColor(uint8 r, uint8 g, uint8 b) {
		return ((((r >> 3) & 0x1F) << 11) | (((g >> 2) & 0x3F) << 5) | ((b >> 3) & 0x1F));
	}

	/**
	 * Convert the given OverlayColor into a RGB triplet. An OverlayColor can
	 * be 8bit, 16bit or 32bit, depending on the target system. The default
	 * implementation takes a 16 bit color value and assumes it to be in 565 format
	 * (that is, 5 bits red, 6 bits green, 5 bits blue).
	 * @see RGBToColor
	 * @see colorToARGB
	 */
	virtual void colorToRGB(OverlayColor color, uint8 &r, uint8 &g, uint8 &b) {
		r = (((color >> 11) & 0x1F) << 3);
		g = (((color >> 5) & 0x3F) << 2);
		b = ((color&0x1F) << 3);
	}

	/**
	* Convert the given ARGB quadruplet into an OverlayColor. A OverlayColor can
	 * be 8bit, 16bit or 32bit, depending on the target system. The default
	 * implementation generates a 16 bit color value, in the 565 format
	 * (that is, 5 bits red, 6 bits green, 5 bits blue).
	 * @note The alpha component, ranges from 0 (transparent) to 255 (opaque).
	 * @see colorToRGB
	 * @see RGBToColor
	 */
	virtual OverlayColor ARGBToColor(uint8 a, uint8 r, uint8 g, uint8 b) {
		return RGBToColor(r, g, b);
	}

	/**
	 * Convert the given OverlayColor into an ARGB quadruplet. An OverlayColor can
	 * be 8bit, 16bit or 32bit, depending on the target system. The default
	 * implementation takes a 16 bit color value and assumes it to be in 565 format
	 * (that is, 5 bits red, 6 bits green, 5 bits blue).
	 * @note The alpha component, ranges from 0 (transparent) to 255 (opaque).
	 * @see ARGBToColor
	 * @see colorToRGB
	 */
	virtual void colorToARGB(OverlayColor color, uint8 &a, uint8 &r, uint8 &g, uint8 &b) {
		colorToRGB(color, r, g, b);
		a = 255;
	}

	//@}



	/** @name Mouse */
	//@{

	/** Show or hide the mouse cursor. */
	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 x 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 (8bit/pixel)
	 * @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 index
	 * @param cursorTargetScale	scale factor which cursor is designed for
	 */
	virtual void setMouseCursor(const byte *buf, uint w, uint h, int hotspotX, int hotspotY, byte keycolor = 255, int cursorTargetScale = 1) = 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 kFeatureCursorHasPalette flag set
	 *
	 * @see setPalette
	 * @see kFeatureCursorHasPalette
	 */
	virtual void setCursorPalette(const byte *colors, uint start, uint num) {};

	/**
	 * Disable or enable cursor palette.
	 *
	 * Backends which implement it should have kFeatureCursorHasPalette flag set
	 *
	 * @param disable  True to disable, false to enable.
	 *
	 * @see setPalette
	 * @see kFeatureCursorHasPalette
	 */
	virtual void disableCursorPalette(bool disable) {};

	//@}



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

	/**
	 * The types of events backends may generate.
	 * @see Event
	 *
	 * @todo Merge EVENT_LBUTTONDOWN, EVENT_RBUTTONDOWN and EVENT_WHEELDOWN;
	 *       likewiese EVENT_LBUTTONUP, EVENT_RBUTTONUP, EVENT_WHEELUP.
	 *       To do that, we just have to add a field to the Event which
	 *       indicates which button was pressed.
	 */
	enum EventType {
		/** A key was pressed, details in Event::kbd. */
		EVENT_KEYDOWN = 1,
		/** A key was released, details in Event::kbd. */
		EVENT_KEYUP = 2,
		/** The mouse moved, details in Event::mouse. */
		EVENT_MOUSEMOVE = 3,
		EVENT_LBUTTONDOWN = 4,
		EVENT_LBUTTONUP = 5,
		EVENT_RBUTTONDOWN = 6,
		EVENT_RBUTTONUP = 7,
		EVENT_WHEELUP = 8,
		EVENT_WHEELDOWN = 9,

		EVENT_QUIT = 10,
		EVENT_SCREEN_CHANGED = 11
	};

	/**
	 * Keyboard modifier flags, used for Event::kbd::flags.
	 */
	enum {
		KBD_CTRL  = 1 << 0,
		KBD_ALT   = 1 << 1,
		KBD_SHIFT = 1 << 2
	};

	/**
	 * Data structure for an event. A pointer to an instance of Event
	 * can be passed to pollEvent.
	 * @todo Rework/document this structure. It should be made 100% clear which
	 *       field is valid for which event type.
	 *       Implementation wise, we might want to use the classic
	 *       union-of-structs trick. It goes roughly like this:
	 *       struct BasicEvent {
	 *       	EventType type;
	 *       };
	 *       struct MouseMovedEvent : BasicEvent {
	 *       	Common::Point pos;
	 *       };
	 *       struct MouseButtonEvent : MouseMovedEvent {
	 *       	int button;
	 *       };
	 *       struct KeyEvent : BasicEvent {
	 *       	...
	 *       };
	 *       ...
	 *       union Event {
	 *          EventType type;
	 *       	MouseMovedEvent mouse;
	 *       	MouseButtonEvent button;
	 *       	KeyEvent key;
	 *       	...
	 *       };
	 */
	struct Event {
		/** The type of the event. */
		EventType type;
		/**
		  * Keyboard data; only valid for keyboard events (EVENT_KEYDOWN and
		  * EVENT_KEYUP). For all other event types, content is undefined.
		  */
		struct {
			/**
			 * Abstract key code (will be the same for any given key regardless
			 * of modifiers being held at the same time.
			 * For example, this is the same for both 'A' and Shift-'A'.
			 * @todo Document which values are to be used for non-ASCII keys
			 * like F1-F10. For now, let's just say that our primary backend
			 * is the SDL one, and it uses the values SDL uses... so until
			 * we fix this, your best bet is to get a copy of SDL_keysym.h
			 * and look at that, if you want to find out a key code.
			 */
			int keycode;
			/**
			 * ASCII-value of the pressed key (if any).
			 * This depends on modifiers, i.e. pressing the 'A' key results in
			 * different values here depending on the status of shift, alt and
			 * caps lock.
			 * For the function keys F1-F9, values of 315-323 are used.
			 */
			uint16 ascii;
			/**
			 * Status of the modifier keys. Bits are set in this for each
			 * pressed modifier
			 * @see KBD_CTRL, KBD_ALT, KBD_SHIFT
			 */
			byte flags;
		} kbd;
		/**
		 * The mouse coordinates, in virtual screen coordinates. Only valid
		 * for mouse events.
		 * Virtual screen coordinates means: the coordinate system of the
		 * screen area as defined by the most recent call to initSize().
		 */
		Common::Point mouse;
	};

	/**
	 * Get the next event in the event queue.
	 * @param event	point to an Event struct, which will be filled with the event data.
	 * @return true if an event was retrieved.
	 */
	virtual bool pollEvent(Event &event) = 0;

	/** Get the number of milliseconds since the program was started. */
	virtual uint32 getMillis() = 0;

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

	/**
	 * Returh the timer manager. For more information, refer to the
	 * TimerManager documentation.
	 */
	virtual Common::TimerManager *getTimerManager() = 0;

	//@}



	/**
	 * @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.
	 *
	 * Hence backends which do not use threads to implement the timers simply
	 * can use dummy implementations for these methods.
	 */
	//@{

	typedef Common::MutexRef	MutexRef;

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

	/**
	 * Lock the given mutex.
	 * @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 */
	//@{

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

	/**
	 * Determine the output sample rate. Audio data provided by the sound
	 * callback will be played using this rate.
	 * @note Client code other than the sound mixer should _not_ use this
	 *       method. Instead, call Mixer::getOutputRate()!
	 * @return the output sample rate
	 */
	virtual int getOutputSampleRate() const = 0;

	//@}



	/**
	 * @name Audio CD
	 * The methods in this group deal with Audio CD playback.
	 * The default implementation simply does nothing.
	 */
	//@{

	/**
	 * Initialise the specified CD drive for audio playback.
	 * @return true if the CD drive was inited succesfully
	 */
	virtual bool openCD(int drive);

	/**
	 * Poll CD status.
	 * @return true if CD audio is playing
	 */
	virtual bool pollCD();

	/**
	 * Start audio CD playback.
	 * @param track			the track to play.
	 * @param num_loops		how often playback should be repeated (-1 = infinitely often).
	 * @param start_frame	the frame at which playback should start (75 frames = 1 second).
	 * @param duration		the number of frames to play.
	 */
	virtual void playCD(int track, int num_loops, int start_frame, int duration);

	/**
	 * Stop audio CD playback.
	 */
	virtual void stopCD();

	/**
	 * Update cdrom audio status.
	 */
	virtual void updateCD();

	//@}



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

	/**
	 * Set a window caption or any other comparable status display to the
	 * given value. The caption must be a pure ASCII string. Passing a
	 * non-ASCII string may lead to unexpected behavior, even crashes.
	 *
	 * In a future revision of this API, this may be changed to allowing
	 * UTF-8 or UTF-16 encoded data, or maybe ISO LATIN 1.
	 *
	 * @param caption	the window caption to use, as an ASCII 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.).
	 *
	 * @note There is a default implementation 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);

	/**
	 * Return the SaveFileManager, used to store and load savestates
	 * and other modifiable persistent game data. For more information,
	 * refer to the TimerManager documentation.
	 */
	virtual Common::SaveFileManager *getSavefileManager() = 0;

	//@}
};


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

#endif