SCI32: "Fix" renderer for PQ4CD

PQ4CD and several other games contain a hack in two renderer
methods to avoid rendering invalid screen items with zero or
negative-dimension target rects. This prevents PQ4CD from
crashing during the fifth phase of target practice.

2 files changed, 26 insertions, 3 deletions

diff --git a/engines/sci/graphics/celobj32.cpp b/engines/sci/graphics/celobj32.cpp
index fe0fbf7cc4..8540b636fc 100644
--- a/engines/sci/graphics/celobj32.cpp
+++ b/engines/sci/graphics/celobj32.cpp
@@ -176,6 +176,10 @@ struct SCALER_Scale {
 	// so just always make the reader decompress an entire
 	// line of source data when scaling
 	_reader(celObj, celObj._width) {
+#ifndef NDEBUG
+		assert(_minX <= _maxX);
+#endif
+
 		// In order for scaling ratios to apply equally across objects that
 		// start at different positions on the screen (like the cels of a
 		// picture), the pixels that are read from the source bitmap must all
@@ -773,6 +777,14 @@ void CelObj::drawUncompHzFlipNoMDNoSkip(Buffer &target, const Common::Rect &targ
 }
 
 void CelObj::scaleDrawNoMD(Buffer &target, const Ratio &scaleX, const Ratio &scaleY, const Common::Rect &targetRect, const Common::Point &scaledPosition) const {
+	// In SSCI the checks are > because their rects are BR-inclusive;
+	// our checks are >= because our rects are BR-exclusive
+	if (g_sci->_features->hasEmptyScaleDrawHack() &&
+		(targetRect.left >= targetRect.right ||
+		 targetRect.top >= targetRect.bottom)) {
+		return;
+	}
+
 	if (_drawMirrored)
 		render<MAPPER_NoMD, SCALER_Scale<true, READER_Compressed> >(target, targetRect, scaledPosition, scaleX, scaleY);
 	else
@@ -780,6 +792,14 @@ void CelObj::scaleDrawNoMD(Buffer &target, const Ratio &scaleX, const Ratio &sca
 }
 
 void CelObj::scaleDrawUncompNoMD(Buffer &target, const Ratio &scaleX, const Ratio &scaleY, const Common::Rect &targetRect, const Common::Point &scaledPosition) const {
+	// In SSCI the checks are > because their rects are BR-inclusive;
+	// our checks are >= because our rects are BR-exclusive
+	if (g_sci->_features->hasEmptyScaleDrawHack() &&
+		(targetRect.left >= targetRect.right ||
+		 targetRect.top >= targetRect.bottom)) {
+		return;
+	}
+
 	if (_drawMirrored) {
 		render<MAPPER_NoMD, SCALER_Scale<true, READER_Uncompressed> >(target, targetRect, scaledPosition, scaleX, scaleY);
 	} else {
diff --git a/engines/sci/graphics/frameout.cpp b/engines/sci/graphics/frameout.cpp
index 749403093f..464b28a2ba 100644
--- a/engines/sci/graphics/frameout.cpp
+++ b/engines/sci/graphics/frameout.cpp
@@ -1168,10 +1168,13 @@ void GfxFrameout::showBits() {
 
 		byte *sourceBuffer = (byte *)_currentBuffer.getPixels() + rounded.top * _currentBuffer.screenWidth + rounded.left;
 
-		// TODO: Sometimes transition screen items generate zero-dimension
-		// show rectangles. Is this a bug?
+		// Sometimes screen items (especially from SCI2.1early transitions, like
+		// in the asteroids minigame in PQ4) generate zero-dimension show
+		// rectangles. In SSCI, zero-dimension rectangles are OK (they just
+		// result in no copy), but OSystem::copyRectToScreen will assert on
+		// them, so we need to check for zero-dimensions rectangles and ignore
+		// them explicitly
 		if (rounded.width() == 0 || rounded.height() == 0) {
-			warning("Zero-dimension show rectangle ignored");
 			continue;
 		}