From bd6748fb5beb9d2f5cb0dd62fce445fe73b4d10e Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 12 Dec 2015 13:17:02 +0200
Subject: [PATCH] Some refactoring of OpenGL code

In preparation for geometry correction
---
 source/main.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/source/main.c b/source/main.c
index 0992542..f4704ae 100644
--- a/source/main.c
+++ b/source/main.c
@@ -63,29 +63,31 @@ static const char *vshader =
 	"#version 150\n"
 	"uniform vec4 geometry;\n"
 	"in vec2 vertex;\n"
+	"in vec2 texture_coord;\n"
 	"out vec2 texcoord;\n"
 	"void main()\n"
 	"{\n"
 	"  gl_Position = vec4((geometry.xy+vertex*geometry.zw)*2.0-1.0, 0.0, 1.0);\n"
-	"  texcoord = vec2(vertex.x, 1.0-vertex.y);\n"
+	"  texcoord = texture_coord;\n"
 	"}\n";
 
 static const char *fshader =
 	"#version 150\n"
-	"uniform sampler2D window;\n"
+	"uniform sampler2D image;\n"
 	"in vec2 texcoord;\n"
 	"out vec4 frag_color;\n"
 	"void main()\n"
 	"{\n"
-	"	frag_color = texture(window, texcoord);\n"
+	"	frag_color = texture(image, texcoord);\n"
 	"}\n";
 
 static const float vertices[] =
 {
-	0.0f, 1.0f,
-	0.0f, 0.0f,
-	1.0f, 1.0f,
-	1.0f, 0.0f
+	/* vertex    texcoord */
+	0.0f, 1.0f,  0.0f, 0.0f,
+	0.0f, 0.0f,  0.0f, 1.0f,
+	1.0f, 1.0f,  1.0f, 0.0f,
+	1.0f, 0.0f,  1.0f, 1.0f
 };
 
 int terminate_requested = 0;
@@ -193,6 +195,8 @@ unsigned link_program(unsigned *shaders, unsigned nshaders)
 	for(i=0; i<nshaders; ++i)
 		glAttachShader(program, shaders[i]);
 	glBindAttribLocation(program, 0, "vertex");
+	glBindAttribLocation(program, 1, "texture_coord");
+	glBindFragDataLocation(program, 0, "frag_color");
 	glLinkProgram(program);
 
 	glGetProgramiv(program, GL_LINK_STATUS, &status);
@@ -211,6 +215,8 @@ unsigned link_program(unsigned *shaders, unsigned nshaders)
 
 int create_gl_resources(Compositor *compositor, CompositedScreen *screen)
 {
+	unsigned stride;
+
 	use_gl(compositor, screen);
 
 	screen->shaders[0] = compile_shader(GL_VERTEX_SHADER, vshader);
@@ -228,10 +234,14 @@ int create_gl_resources(Compositor *compositor, CompositedScreen *screen)
 	glBindBuffer(GL_ARRAY_BUFFER, screen->vertex_buffer);
 	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
 
+	stride = 4*sizeof(float);
 	glGenVertexArrays(1, &screen->vertex_array);
 	glBindVertexArray(screen->vertex_array);
-	glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, NULL);
+	glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, stride, NULL);
 	glEnableVertexAttribArray(0);
+	glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, stride, (void *)(2*sizeof(float)));
+	glEnableVertexAttribArray(1);
+	glBindVertexArray(0);
 
 	glBindBuffer(GL_ARRAY_BUFFER, 0);
 
-- 
2.43.0