SCI: Implementation of kCelInfo subop 4

kCelInfo subop 4 returns the pixel color at the
passed in x,y coordinates for the passed in view,
loop, cel.  Shivers uses this function for the
red door puzzle, room 23601 to determine what
blocks on the puzzle board are already occupied
by pieces.

5 files changed, 34 insertions, 5 deletions

diff --git a/engines/sci/engine/kgraphics.cpp b/engines/sci/engine/kgraphics.cpp
index c60c0a44b9..ce670b21fe 100644
--- a/engines/sci/engine/kgraphics.cpp
+++ b/engines/sci/engine/kgraphics.cpp
@@ -1471,10 +1471,8 @@ reg_t kSetShowStyle(EngineState *s, int argc, reg_t *argv) {
 }
 
 reg_t kCelInfo(EngineState *s, int argc, reg_t *argv) {
-	// TODO: This is all a stub/skeleton, thus we're invoking kStub() for now
-	kStub(s, argc, argv);
-
-	// Used by Shivers 1, room 23601
+	// Used by Shivers 1, room 23601 to determine what blocks on the red door puzzle board
+	// are occupied by pieces already
 
 	// 6 arguments, all integers:
 	// argv[0] - subop (0 - 4). It's constantly called with 4 in Shivers 1
@@ -1490,7 +1488,21 @@ reg_t kCelInfo(EngineState *s, int argc, reg_t *argv) {
 	// 2, 3 - nop
 	// 4 - return value of pixel at x, y
 
-	return s->r_acc;
+	switch (argv[0].toUint16()) {
+		case 4: {
+			GuiResourceId viewId = argv[1].toSint16();
+			int16 loopNo = argv[2].toSint16();
+			int16 celNo = argv[3].toSint16();
+			int16 x = argv[4].toUint16();
+			int16 y = argv[5].toUint16();
+			byte color = g_sci->_gfxCache->kernelViewGetColorAtCoordinate(viewId, loopNo, celNo, x, y);
+			return make_reg(0, color);
+		}
+		default: {
+			kStub(s, argc, argv);
+			return s->r_acc;
+		}
+	}
 }
 
 reg_t kScrollWindow(EngineState *s, int argc, reg_t *argv) {
diff --git a/engines/sci/graphics/cache.cpp b/engines/sci/graphics/cache.cpp
index d2bd76ac99..55f8624c49 100644
--- a/engines/sci/graphics/cache.cpp
+++ b/engines/sci/graphics/cache.cpp
@@ -102,4 +102,8 @@ int16 GfxCache::kernelViewGetCelCount(GuiResourceId viewId, int16 loopNo) {
 	return getView(viewId)->getCelCount(loopNo);
 }
 
+byte GfxCache::kernelViewGetColorAtCoordinate(GuiResourceId viewId, int16 loopNo, int16 celNo, int16 x, int16 y) {
+	return getView(viewId)->getColorAtCoordinate(loopNo, celNo, x, y);
+}
+
 } // End of namespace Sci
diff --git a/engines/sci/graphics/cache.h b/engines/sci/graphics/cache.h
index c090cda7d7..2f462fe042 100644
--- a/engines/sci/graphics/cache.h
+++ b/engines/sci/graphics/cache.h
@@ -49,6 +49,8 @@ public:
 	int16 kernelViewGetLoopCount(GuiResourceId viewId);
 	int16 kernelViewGetCelCount(GuiResourceId viewId, int16 loopNo);
 
+	byte kernelViewGetColorAtCoordinate(GuiResourceId viewId, int16 loopNo, int16 celNo, int16 x, int16 y);
+
 private:
 	void purgeFontCache();
 	void purgeViewCache();
diff --git a/engines/sci/graphics/view.cpp b/engines/sci/graphics/view.cpp
index a0d5b51a2b..d5c52bfb59 100644
--- a/engines/sci/graphics/view.cpp
+++ b/engines/sci/graphics/view.cpp
@@ -837,4 +837,13 @@ void GfxView::adjustBackUpscaledCoordinates(int16 &y, int16 &x) {
 	_screen->adjustBackUpscaledCoordinates(y, x, _sci2ScaleRes);
 }
 
+byte GfxView::getColorAtCoordinate(int16 loopNo, int16 celNo, int16 x, int16 y) {
+	const CelInfo *celInfo = getCelInfo(loopNo, celNo);
+	const byte *bitmap = getBitmap(loopNo, celNo);
+	const int16 celWidth = celInfo->width;
+
+	bitmap += (celWidth * y);
+	return bitmap[x];
+}
+
 } // End of namespace Sci
diff --git a/engines/sci/graphics/view.h b/engines/sci/graphics/view.h
index 19ef2e62f8..d3473f1024 100644
--- a/engines/sci/graphics/view.h
+++ b/engines/sci/graphics/view.h
@@ -85,6 +85,8 @@ public:
 	void adjustToUpscaledCoordinates(int16 &y, int16 &x);
 	void adjustBackUpscaledCoordinates(int16 &y, int16 &x);
 
+	byte getColorAtCoordinate(int16 loopNo, int16 celNo, int16 x, int16 y);
+
 private:
 	void initData(GuiResourceId resourceId);
 	void unpackCel(int16 loopNo, int16 celNo, byte *outPtr, uint32 pixelCount);