AGI: Check xPos/yPos when building sprite lists

And ignore sprites, that are placed outside of visual screen
Fixes memory corruption during intro of fan made Get Outta SQ game.
Original AGI did not do checks at all.

1 files changed, 22 insertions, 0 deletions

diff --git a/engines/agi/sprite.cpp b/engines/agi/sprite.cpp
index c68641fb33..09935c93f9 100644
--- a/engines/agi/sprite.cpp
+++ b/engines/agi/sprite.cpp
@@ -106,6 +106,28 @@ void SpritesMgr::buildSpriteListAdd(uint16 givenOrderNr, ScreenObjEntry *screenO
 	spriteEntry.yPos = (screenObj->yPos) - (screenObj->ySize) + 1;
 	spriteEntry.xSize = screenObj->xSize;
 	spriteEntry.ySize = screenObj->ySize;
+
+	// Checking, if xPos/yPos/right/bottom are valid and do not go outside of playscreen (visual screen)
+	// Original AGI did not do this (but it then resulted in memory corruption)
+	if (spriteEntry.xPos < 0) {
+		warning("buildSpriteListAdd(): ignoring screen obj %d, b/c xPos < 0", screenObj->objectNr, spriteEntry.xPos);
+		return;
+	}
+	if (spriteEntry.yPos < 0) {
+		warning("buildSpriteListAdd(): ignoring screen obj %d, b/c yPos (%d) < 0", screenObj->objectNr, spriteEntry.yPos);
+		return;
+	}
+	int16 xRight = spriteEntry.xPos + spriteEntry.xSize;
+	if (xRight > SCRIPT_HEIGHT) {
+		warning("buildSpriteListAdd(): ignoring screen obj %d, b/c rightPos > %d", screenObj->objectNr, xRight, SCRIPT_WIDTH);
+		return;
+	}
+	int16 yBottom = spriteEntry.yPos + spriteEntry.ySize;
+	if (yBottom > SCRIPT_HEIGHT) {
+		warning("buildSpriteListAdd(): ignoring screen obj %d, b/c bottomPos > %d", screenObj->objectNr, yBottom, SCRIPT_HEIGHT);
+		return;
+	}
+
 //	warning("list-add: %d, %d, original yPos: %d, ySize: %d", spriteEntry.xPos, spriteEntry.yPos, screenObj->yPos, screenObj->ySize);
 	spriteEntry.backgroundBuffer = (uint8 *)malloc(spriteEntry.xSize * spriteEntry.ySize * 2); // for visual + priority data
 	assert(spriteEntry.backgroundBuffer);