From 400ac04d42bfa058e33f61176a53148a39b7ca34 Mon Sep 17 00:00:00 2001
From: Jeffrey Pfau <jeffrey@endrift.com>
Date: Tue, 16 Aug 2016 22:40:03 -0700
Subject: [PATCH] GBA Video: Fix some small cases in sprite optimization

---
 src/gba/renderers/software-obj.c | 60 +++++++++++++++++---------------
 1 file changed, 32 insertions(+), 28 deletions(-)

diff --git a/src/gba/renderers/software-obj.c b/src/gba/renderers/software-obj.c
index c32d2af9d..3a713743b 100644
--- a/src/gba/renderers/software-obj.c
+++ b/src/gba/renderers/software-obj.c
@@ -208,35 +208,39 @@ int GBAVideoSoftwareRendererPreprocessSprite(struct GBAVideoSoftwareRenderer* re
 		}
 
 		// Clip off early pixels
-		if ((xAccum >> 8) < -(width >> 1)) {
-			int32_t diffX = -(width << 7) - xAccum;
-			int32_t x = mat.a ? diffX / mat.a : 0;
-			xAccum += mat.a * x;
-			yAccum += mat.c * x;
-			outX += x;
-			inX += x;
-		} else if ((xAccum >> 8) >= (width >> 1)) {
-			int32_t diffX = (width << 7) - xAccum;
-			int32_t x = mat.a ? diffX / mat.a : 0;
-			xAccum += mat.a * x;
-			yAccum += mat.c * x;
-			outX += x;
-			inX += x;
+		if (mat.a) {
+			if ((xAccum >> 8) < -(width >> 1)) {
+				int32_t diffX = -(width << 7) - xAccum - 1;
+				int32_t x = mat.a ? diffX / mat.a : 0;
+				xAccum += mat.a * x;
+				yAccum += mat.c * x;
+				outX += x;
+				inX += x;
+			} else if ((xAccum >> 8) >= (width >> 1)) {
+				int32_t diffX = (width << 7) - xAccum;
+				int32_t x = mat.a ? diffX / mat.a : 0;
+				xAccum += mat.a * x;
+				yAccum += mat.c * x;
+				outX += x;
+				inX += x;
+			}
 		}
-		if ((yAccum >> 8) < -(height >> 1)) {
-			int32_t diffY = -(height << 7) - yAccum;
-			int32_t y = mat.c ? diffY / mat.c : 0;
-			xAccum += mat.a * y;
-			yAccum += mat.c * y;
-			outX += y;
-			inX += y;
-		} else if ((yAccum >> 8) >= (height >> 1)) {
-			int32_t diffY = (height << 7) - yAccum;
-			int32_t y = mat.c ? diffY / mat.c : 0;
-			xAccum += mat.a * y;
-			yAccum += mat.c * y;
-			outX += y;
-			inX += y;
+		if (mat.c) {
+			if ((yAccum >> 8) < -(height >> 1)) {
+				int32_t diffY = -(height << 7) - yAccum - 1;
+				int32_t y = mat.c ? diffY / mat.c : 0;
+				xAccum += mat.a * y;
+				yAccum += mat.c * y;
+				outX += y;
+				inX += y;
+			} else if ((yAccum >> 8) >= (height >> 1)) {
+				int32_t diffY = (height << 7) - yAccum;
+				int32_t y = mat.c ? diffY / mat.c : 0;
+				xAccum += mat.a * y;
+				yAccum += mat.c * y;
+				outX += y;
+				inX += y;
+			}
 		}
 
 		if (!GBAObjAttributesAIs256Color(sprite->a)) {