From a769c156547f85817bb53e729614cdb7fd29b324 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Tue, 18 Mar 2014 23:18:56 +0100
Subject: [PATCH 1/1] Make VAOs persistent.

Seemingly helps ~0.5 ms/frame (which is quite significant for small
resolutions) on the demo applications on my NVidia card.
---
 effect_chain.cpp | 60 ++++++++++++++++++++++++++++--------------------
 effect_chain.h   |  7 ++++++
 2 files changed, 42 insertions(+), 25 deletions(-)

diff --git a/effect_chain.cpp b/effect_chain.cpp
index 8d3c61d..487d7b7 100644
--- a/effect_chain.cpp
+++ b/effect_chain.cpp
@@ -53,6 +53,15 @@ EffectChain::~EffectChain()
 		delete nodes[i];
 	}
 	for (unsigned i = 0; i < phases.size(); ++i) {
+		glBindVertexArray(phases[i]->vao);
+		check_error();
+
+		cleanup_vertex_attribute(phases[i]->glsl_program_num, "position", phases[i]->position_vbo);
+		cleanup_vertex_attribute(phases[i]->glsl_program_num, "texcoord", phases[i]->texcoord_vbo);
+
+		glBindVertexArray(0);
+		check_error();
+
 		resource_pool->release_glsl_program(phases[i]->glsl_program_num);
 		delete phases[i];
 	}
@@ -287,6 +296,27 @@ void EffectChain::compile_glsl_program(Phase *phase)
 	frag_shader.append(read_file("footer.frag"));
 
 	phase->glsl_program_num = resource_pool->compile_glsl_program(read_file("vs.vert"), frag_shader);
+
+	// Prepare the geometry for the fullscreen quad used in this phase.
+	// (We have separate VAOs per shader, since the bindings can in theory
+	// be different.)
+	float vertices[] = {
+		0.0f, 1.0f,
+		0.0f, 0.0f,
+		1.0f, 1.0f,
+		1.0f, 0.0f
+	};
+
+	glGenVertexArrays(1, &phase->vao);
+	check_error();
+	glBindVertexArray(phase->vao);
+	check_error();
+
+	phase->position_vbo = fill_vertex_attribute(phase->glsl_program_num, "position", 2, GL_FLOAT, sizeof(vertices), vertices);
+	phase->texcoord_vbo = fill_vertex_attribute(phase->glsl_program_num, "texcoord", 2, GL_FLOAT, sizeof(vertices), vertices);  // Same as vertices.
+
+	glBindVertexArray(0);
+	check_error();
 }
 
 // Construct GLSL programs, starting at the given effect and following
@@ -1532,39 +1562,15 @@ void EffectChain::render_to_fbo(GLuint dest_fbo, unsigned width, unsigned height
 			}
 		}
 
-		// Now draw!
-		float vertices[] = {
-			0.0f, 1.0f,
-			0.0f, 0.0f,
-			1.0f, 1.0f,
-			1.0f, 0.0f
-		};
-
-		GLuint vao;
-		glGenVertexArrays(1, &vao);
-		check_error();
-		glBindVertexArray(vao);
+		glBindVertexArray(phases[phase]->vao);
 		check_error();
-
-		GLuint position_vbo = fill_vertex_attribute(glsl_program_num, "position", 2, GL_FLOAT, sizeof(vertices), vertices);
-		GLuint texcoord_vbo = fill_vertex_attribute(glsl_program_num, "texcoord", 2, GL_FLOAT, sizeof(vertices), vertices);  // Same as vertices.
-
 		glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 		check_error();
 
-		cleanup_vertex_attribute(glsl_program_num, "position", position_vbo);
-		cleanup_vertex_attribute(glsl_program_num, "texcoord", texcoord_vbo);
-
-		glUseProgram(0);
-		check_error();
-
 		for (unsigned i = 0; i < phases[phase]->effects.size(); ++i) {
 			Node *node = phases[phase]->effects[i];
 			node->effect->clear_gl_state();
 		}
-
-		glDeleteVertexArrays(1, &vao);
-		check_error();
 	}
 
 	for (map<Phase *, GLuint>::const_iterator texture_it = output_textures.begin();
@@ -1575,6 +1581,10 @@ void EffectChain::render_to_fbo(GLuint dest_fbo, unsigned width, unsigned height
 
 	glBindFramebuffer(GL_FRAMEBUFFER, 0);
 	check_error();
+	glBindVertexArray(0);
+	check_error();
+	glUseProgram(0);
+	check_error();
 }
 
 }  // namespace movit
diff --git a/effect_chain.h b/effect_chain.h
index 505e55a..9051195 100644
--- a/effect_chain.h
+++ b/effect_chain.h
@@ -99,6 +99,13 @@ struct Phase {
 	// Identifier used to create unique variables in GLSL.
 	// Unique per-phase to increase cacheability of compiled shaders.
 	std::map<Node *, std::string> effect_ids;
+
+	// The geometry needed to draw this quad, bound to the vertex array
+	// object. (Seemingly it's actually a win not to upload geometry every
+	// frame, even for something as small as a quad, due to fewer state
+	// changes.)
+	GLuint vao;
+	GLuint position_vbo, texcoord_vbo;
 };
 
 class EffectChain {
-- 
2.39.5