From 10b9e833535eeddeb8e4e67f7a5126eed03d706e Mon Sep 17 00:00:00 2001
From: Henrik Rydgard <hrydgard@gmail.com>
Date: Wed, 4 Dec 2013 13:16:22 +0100
Subject: [PATCH] Dest alpha mask: Try some rules that seem to make sense from
 what we know now.

---
 GPU/GLES/StateMapping.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/GPU/GLES/StateMapping.cpp b/GPU/GLES/StateMapping.cpp
index 0243b9d167..8d862c5eb4 100644
--- a/GPU/GLES/StateMapping.cpp
+++ b/GPU/GLES/StateMapping.cpp
@@ -339,6 +339,19 @@ void TransformDrawEngine::ApplyDrawState(int prim) {
 		bool gmask = ((gstate.pmskc >> 8) & 0xFF) < 128;
 		bool bmask = ((gstate.pmskc >> 16) & 0xFF) < 128;
 		bool amask = (gstate.pmska & 0xFF) < 128;
+
+		if (gstate.isModeClear()) {
+			// Clear mode? Obey the clear mode alpha mask (works opposite)
+			if (gstate.isClearModeAlphaMask()) {
+				amask = false;
+			}
+		} else {
+			// Let's not write to alpha if stencil isn't enabled.
+			if (!gstate.isStencilTestEnabled()) {
+				amask = false;
+			}
+		}
+
 		glstate.colorMask.set(rmask, gmask, bmask, amask);
 
 		// Stencil Test