From e2058f0da6ebb223992e15b26dbba6d20858ca2c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1=C5=A1=20Mal=C3=BD?= <tomas.maly@melown.com>
Date: Mon, 9 Jul 2018 13:44:46 +0200
Subject: [PATCH] surface shader - fix uniform control flow for texture
 accesses

---
 .../data/shaders/surface.frag.glsl            | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/browser/src/vts-librenderer/data/shaders/surface.frag.glsl b/browser/src/vts-librenderer/data/shaders/surface.frag.glsl
index 886d2ca2..b38aa6ad 100644
--- a/browser/src/vts-librenderer/data/shaders/surface.frag.glsl
+++ b/browser/src/vts-librenderer/data/shaders/surface.frag.glsl
@@ -16,22 +16,25 @@ void main()
 {
     // texture color
     vec4 color = texture(texColor, varUvTex);
-    if (uniFlags.y > 0)
-        color = color.rrra; // monochromatic texture
+
+    // mask
+    if (uniFlags.x > 0)
+    {
+        if (texture(texMask, varUvTex).r < 0.5)
+            discard;
+    }
 
     // uv clipping
+    // uv clipping must go after all texture accesses to allow for computation of derivatives in uniform control flow
     if (varUvClip.x < uniUvClip.x
             || varUvClip.y < uniUvClip.y
             || varUvClip.x > uniUvClip.z
             || varUvClip.y > uniUvClip.w)
         discard;
 
-    // mask
-    if (uniFlags.x > 0)
-    {
-        if (texture(texMask, varUvTex).r < 0.5)
-            discard;
-    }
+    // monochromatic texture
+    if (uniFlags.y > 0)
+        color = color.rrra;
 
     // base color
     if (uniFlags.z > 0)