WINTERMUTE: Fix offset calculation with partial rects when sprites ar…

…e mirrored.

This fixes the dress bug, aka Rosemary appearing "jigsawed" when passing
over her with the cursor when she is facing east.
See bug #3592907

engines/wintermute/graphics/transparent_surface.cpp

@@ -309,7 +309,19 @@ Common::Rect TransparentSurface::blit(Graphics::Surface &target, int posX, int p
 	}
 
 	if (pPartRect) {
-		srcImage.pixels = getBasePtr(pPartRect->left, pPartRect->top);
+
+		int xOffset = pPartRect->left;
+		int yOffset = pPartRect->top;
+
+		if (flipping & FLIP_V) {
+			yOffset = srcImage.h - pPartRect->bottom;
+		}
+
+		if (flipping & FLIP_H) {
+			xOffset = srcImage.w - pPartRect->right;
+		}
+
+		srcImage.pixels = getBasePtr(xOffset, yOffset);
 		srcImage.w = pPartRect->width();
 		srcImage.h = pPartRect->height();