SCI32: Don't crash on zero-dimension show rects

In the original engine this would have simply resulted in no draw,
but ScummVM is more strict about it. It is not 100% clear whether
these are normal and should be allowed or not, so for the moment
we'll emit a warning whenever a zero-dimension show rect is seen.

For now they only seem to be generated by plane transitions, and
these zero-dimension screen items cannot simply be omitted because
the 2.1early transitions code requires a fixed number of screen
items per step.

1 files changed, 7 insertions, 0 deletions

diff --git a/engines/sci/graphics/frameout.cpp b/engines/sci/graphics/frameout.cpp
index 7ea159f45d..1decfa03a9 100644
--- a/engines/sci/graphics/frameout.cpp
+++ b/engines/sci/graphics/frameout.cpp
@@ -1143,6 +1143,13 @@ 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?
+		if (rounded.width() == 0 || rounded.height() == 0) {
+			warning("Zero-dimension show rectangle ignored");
+			continue;
+		}
+
 		g_system->copyRectToScreen(sourceBuffer, _currentBuffer.screenWidth, rounded.left, rounded.top, rounded.width(), rounded.height());
 	}