From 5626b74b79119b37a980196ab2ea1749e6091e13 Mon Sep 17 00:00:00 2001
From: Alexander Szpakowski <amaranth72@gmail.com>
Date: Fri, 21 Dec 2012 17:43:47 -0400
Subject: [PATCH] reduced unnecessary usage of glUseProgram, shadereffect is
 now properly detached in unloadVolatile and reattached if necessary in
 loadVolatile, made current and max texture units static to prevent different
 shaders from overwriting the value of different texture units

---
 src/modules/graphics/opengl/ShaderEffect.cpp | 55 ++++++++++++++------
 src/modules/graphics/opengl/ShaderEffect.h   |  4 +-
 2 files changed, 41 insertions(+), 18 deletions(-)

diff --git a/src/modules/graphics/opengl/ShaderEffect.cpp b/src/modules/graphics/opengl/ShaderEffect.cpp
index b17b6fead..2a5725712 100644
--- a/src/modules/graphics/opengl/ShaderEffect.cpp
+++ b/src/modules/graphics/opengl/ShaderEffect.cpp
@@ -27,17 +27,23 @@ namespace
 // reattaches the originally active program when destroyed
 struct TemporaryAttacher
 {
-	TemporaryAttacher(love::graphics::opengl::ShaderEffect *sp) : s(sp)
+	TemporaryAttacher(love::graphics::opengl::ShaderEffect *sp)
+	: cureffect(sp)
+	, preveffect(love::graphics::opengl::ShaderEffect::current)
 	{
-		glGetIntegerv(GL_CURRENT_PROGRAM, &activeProgram);
-		s->attach();
+		cureffect->attach();
 	}
+	
 	~TemporaryAttacher()
 	{
-		glUseProgram(activeProgram);
+		if (preveffect != NULL)
+			preveffect->attach();
+		else
+			cureffect->detach();
 	}
-	love::graphics::opengl::ShaderEffect *s;
-	GLint activeProgram;
+	
+	love::graphics::opengl::ShaderEffect *cureffect;
+	love::graphics::opengl::ShaderEffect *preveffect;
 };
 } // anonymous namespace
 
@@ -50,16 +56,26 @@ namespace opengl
 
 ShaderEffect *ShaderEffect::current = NULL;
 
+GLint ShaderEffect::_current_texture_unit = 0;
+GLint ShaderEffect::_max_texture_units = 0;
+
 ShaderEffect::ShaderEffect(const std::string &vertcode, const std::string &fragcode)
 	: _program(0)
 	, _vertcode(vertcode)
 	, _fragcode(fragcode)
-	, _current_texture_unit(0)
 {
 	glGetIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, &_max_texture_units);
 	loadVolatile();
 }
 
+ShaderEffect::~ShaderEffect()
+{
+	if (current == this)
+		detach();
+	
+	unloadVolatile();
+}
+
 GLint ShaderEffect::getTextureUnit(const std::string &name)
 {
 	std::map<std::string, GLint>::const_iterator it = _texture_unit_pool.find(name);
@@ -68,7 +84,7 @@ GLint ShaderEffect::getTextureUnit(const std::string &name)
 		return it->second;
 	
 	if (++_current_texture_unit >= _max_texture_units)
-		throw love::Exception("No more texture units available");
+		throw love::Exception("No more texture units available for shaders");
 	
 	_texture_unit_pool[name] = _current_texture_unit;
 	return _current_texture_unit;
@@ -149,7 +165,7 @@ void ShaderEffect::createProgram(const std::vector<GLuint> &shaders)
 }
 
 bool ShaderEffect::loadVolatile()
-{	
+{
 	std::vector<GLuint> shaders;
 	
 	if (_vertcode.length() > 0)
@@ -177,19 +193,22 @@ bool ShaderEffect::loadVolatile()
 	std::vector<GLuint>::iterator it;
 	for (it = shaders.begin(); it != shaders.end(); ++it)
 		glDeleteShader(*it);
+	
+	if (current == this)
+		glUseProgram(_program);
 
 	return true;
 }
 
-ShaderEffect::~ShaderEffect()
-{
-	unloadVolatile();
-}
-
 void ShaderEffect::unloadVolatile()
 {
+	if (current == this)
+		glUseProgram(0);
+	
 	if (_program != 0)
 		glDeleteProgram(_program);
+	
+	_program = 0;
 }
 
 std::string ShaderEffect::getGLSLVersion()
@@ -232,13 +251,17 @@ std::string ShaderEffect::getWarnings() const
 
 void ShaderEffect::attach()
 {
-	glUseProgram(_program);
+	if (current != this)
+		glUseProgram(_program);
+	
 	current = this;
 }
 
 void ShaderEffect::detach()
 {
-	glUseProgram(0);
+	if (current != NULL)
+		glUseProgram(0);
+	
 	current = NULL;
 }
 
diff --git a/src/modules/graphics/opengl/ShaderEffect.h b/src/modules/graphics/opengl/ShaderEffect.h
index c270f48f2..88e706dfe 100644
--- a/src/modules/graphics/opengl/ShaderEffect.h
+++ b/src/modules/graphics/opengl/ShaderEffect.h
@@ -72,9 +72,9 @@ private:
 	std::map<std::string, GLint> _uniforms;
 
 	// texture unit pool for setting images
+	static GLint _current_texture_unit;
+	static GLint _max_texture_units;
 	std::map<std::string, GLint> _texture_unit_pool;
-	GLint _current_texture_unit;
-	GLint _max_texture_units;
 	GLint getTextureUnit(const std::string &name);
 	
 	void sendTexture(const std::string &name, GLuint texture);