SH-1903 Don't use indexed texture rendering when GL version is < 3.1 (fixes bad performance on cards with old drivers)

2 files changed, 16 insertions, 1 deletions

diff --git a/indra/llrender/llglslshader.cpp b/indra/llrender/llglslshader.cpp
index 8e99f62de6..ad2c662dfc 100644
--- a/indra/llrender/llglslshader.cpp
+++ b/indra/llrender/llglslshader.cpp
@@ -109,6 +109,11 @@ BOOL LLGLSLShader::createShader(vector<string> * attributes,
 	// Create program
 	mProgramObject = glCreateProgramObjectARB();
 	
+	if (gGLManager.mGLVersion < 3.1f)
+	{ //force indexed texture channels to 1 if GL version is old (performance improvement for drivers with poor branching shader model support)
+		mFeatures.mIndexedTextureChannels = llmin(mFeatures.mIndexedTextureChannels, 1);
+	}
+
 	//compile new source
 	vector< pair<string,GLenum> >::iterator fileIter = mShaderFiles.begin();
 	for ( ; fileIter != mShaderFiles.end(); fileIter++ )
@@ -131,6 +136,11 @@ BOOL LLGLSLShader::createShader(vector<string> * attributes,
 		return FALSE;
 	}
 
+	if (gGLManager.mGLVersion < 3.1f)
+	{ //attachShaderFeatures may have set the number of indexed texture channels, so set to 1 again
+		mFeatures.mIndexedTextureChannels = llmin(mFeatures.mIndexedTextureChannels, 1);
+	}
+
 	// Map attributes and uniforms
 	if (success)
 	{
diff --git a/indra/llrender/llshadermgr.cpp b/indra/llrender/llshadermgr.cpp
index bdc103b917..3910cd779c 100644
--- a/indra/llrender/llshadermgr.cpp
+++ b/indra/llrender/llshadermgr.cpp
@@ -524,7 +524,12 @@ GLhandleARB LLShaderMgr::loadShaderFile(const std::string& filename, S32 & shade
 		text[count++] = strdup("{\n");
 		
 		
-		if (gGLManager.mGLVersion >= 3.f)
+		if (texture_index_channels == 1)
+		{ //don't use flow control, that's silly
+			text[count++] = strdup("return texture2D(tex0, texcoord);\n");
+			text[count++] = strdup("}\n");
+		}
+		else if (gGLManager.mGLVersion >= 3.f)
 		{ 
 			text[count++] = strdup("\tswitch (int(vary_texture_index+0.25))\n");
 			text[count++] = strdup("\t{\n");