From b19cff8a08a03b39653ea16ec5f51a2c80c5f2d1 Mon Sep 17 00:00:00 2001
From: "Unknown W. Brackets" <checkins@unknownbrackets.org>
Date: Wed, 3 Dec 2014 23:24:58 -0800
Subject: [PATCH] OGL: Use a fixed VAO for attributeless rendering.

Instead of abusing whatever VAO is previously bound, which might have
enabled arrays.

Only used in one instance currently, which fixes a crash with older
NVIDIA drivers.
---
 Source/Core/VideoBackends/OGL/GLUtil.cpp      | 31 +++++++++++++++++++
 Source/Core/VideoBackends/OGL/GLUtil.h        |  5 +++
 .../Core/VideoBackends/OGL/PostProcessing.cpp |  2 ++
 Source/Core/VideoBackends/OGL/Render.cpp      |  2 ++
 4 files changed, 40 insertions(+)

diff --git a/Source/Core/VideoBackends/OGL/GLUtil.cpp b/Source/Core/VideoBackends/OGL/GLUtil.cpp
index bfd6170839..f91b079c3b 100644
--- a/Source/Core/VideoBackends/OGL/GLUtil.cpp
+++ b/Source/Core/VideoBackends/OGL/GLUtil.cpp
@@ -16,6 +16,8 @@
 #include "VideoCommon/VideoConfig.h"
 
 cInterfaceBase *GLInterface;
+static GLuint attributelessVAO = 0;
+static GLuint attributelessVBO = 0;
 
 namespace OGL
 {
@@ -113,3 +115,32 @@ GLuint OpenGL_CompileProgram(const char* vertexShader, const char* fragmentShade
 	return programID;
 }
 
+static void CreateAttributelessVAO()
+{
+	glGenVertexArrays(1, &attributelessVAO);
+
+	// In a compatibility context, we require a valid, bound array buffer.
+	glGenBuffers(1, &attributelessVBO);
+
+	// Initialize the buffer with nothing.
+	glBindBuffer(GL_ARRAY_BUFFER, attributelessVBO);
+	glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat), nullptr, GL_STATIC_DRAW);
+
+	// We must also define vertex attribute 0.
+	glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, nullptr);
+}
+
+void OpenGL_BindAttributelessVAO()
+{
+	if (attributelessVAO == 0)
+		CreateAttributelessVAO();
+
+	glBindVertexArray(attributelessVAO);
+	glBindBuffer(GL_ARRAY_BUFFER, attributelessVBO);
+}
+
+void OpenGL_DeleteAttributelessVAO()
+{
+	glDeleteVertexArrays(1, &attributelessVAO);
+	glDeleteBuffers(1, &attributelessVBO);
+}
diff --git a/Source/Core/VideoBackends/OGL/GLUtil.h b/Source/Core/VideoBackends/OGL/GLUtil.h
index 8bcfb06886..3d7e562971 100644
--- a/Source/Core/VideoBackends/OGL/GLUtil.h
+++ b/Source/Core/VideoBackends/OGL/GLUtil.h
@@ -18,6 +18,11 @@ void InitInterface();
 // Helpers
 GLuint OpenGL_CompileProgram(const char *vertexShader, const char *fragmentShader);
 
+// Binds (and creates, if necessary) a VAO and VBO suitable for attributeless rendering.
+void OpenGL_BindAttributelessVAO();
+// Deletes any existing VAO / VBO that has been created.
+void OpenGL_DeleteAttributelessVAO();
+
 // this should be removed in future, but as long as glsl is unstable, we should really read this messages
 #if defined(_DEBUG) || defined(DEBUGFAST)
 #define DEBUG_GLSL 1
diff --git a/Source/Core/VideoBackends/OGL/PostProcessing.cpp b/Source/Core/VideoBackends/OGL/PostProcessing.cpp
index 80bdf8eef4..74fd93147b 100644
--- a/Source/Core/VideoBackends/OGL/PostProcessing.cpp
+++ b/Source/Core/VideoBackends/OGL/PostProcessing.cpp
@@ -72,6 +72,8 @@ void OpenGLPostProcessing::BlitFromTexture(TargetRectangle src, TargetRectangle
 
 	if (m_attribute_workaround)
 		glBindVertexArray(m_attribute_vao);
+	else
+		OpenGL_BindAttributelessVAO();
 
 	m_shader.Bind();
 
diff --git a/Source/Core/VideoBackends/OGL/Render.cpp b/Source/Core/VideoBackends/OGL/Render.cpp
index f33c59899c..c14753039d 100644
--- a/Source/Core/VideoBackends/OGL/Render.cpp
+++ b/Source/Core/VideoBackends/OGL/Render.cpp
@@ -686,6 +686,8 @@ void Renderer::Shutdown()
 
 	delete m_post_processor;
 	m_post_processor = nullptr;
+
+	OpenGL_DeleteAttributelessVAO();
 }
 
 void Renderer::Init()