From dc1b9ce7f0fad9164cf94b7798a60fca3fb56e88 Mon Sep 17 00:00:00 2001
From: Camilla Berglund <elmindreda@elmindreda.org>
Date: Sat, 7 Nov 2015 20:39:25 +0100
Subject: [PATCH] Move simple example to GL2

---
 examples/simple.c | 91 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 75 insertions(+), 16 deletions(-)

diff --git a/examples/simple.c b/examples/simple.c
index a06e7cc6..c789d1af 100644
--- a/examples/simple.c
+++ b/examples/simple.c
@@ -27,9 +27,40 @@
 #include <glad/glad.h>
 #include <GLFW/glfw3.h>
 
+#include "linmath.h"
+
 #include <stdlib.h>
 #include <stdio.h>
 
+static const struct
+{
+    float x, y;
+    float r, g, b;
+} vertices[3] =
+{
+    { -0.6f, -0.4f, 1.f, 0.f, 0.f },
+    {  0.6f, -0.4f, 0.f, 1.f, 0.f },
+    {   0.f,  0.6f, 0.f, 0.f, 1.f }
+};
+
+static const char* vertex_shader_text =
+"uniform mat4 MVP;\n"
+"attribute vec3 vCol;\n"
+"attribute vec2 vPos;\n"
+"varying vec3 color;\n"
+"void main()\n"
+"{\n"
+"    gl_Position = MVP * vec4(vPos, 0.0, 1.0);\n"
+"    color = vCol;\n"
+"}\n";
+
+static const char* fragment_shader_text =
+"varying vec3 color;\n"
+"void main()\n"
+"{\n"
+"    gl_FragColor = vec4(color, 1.0);\n"
+"}\n";
+
 static void error_callback(int error, const char* description)
 {
     fprintf(stderr, "Error: %s\n", description);
@@ -44,12 +75,17 @@ static void key_callback(GLFWwindow* window, int key, int scancode, int action,
 int main(void)
 {
     GLFWwindow* window;
+    GLuint vertex_buffer, vertex_shader, fragment_shader, program;
+    GLint mvp_location, vpos_location, vcol_location;
 
     glfwSetErrorCallback(error_callback);
 
     if (!glfwInit())
         exit(EXIT_FAILURE);
 
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
+    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
+
     window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
     if (!window)
     {
@@ -57,16 +93,47 @@ int main(void)
         exit(EXIT_FAILURE);
     }
 
+    glfwSetKeyCallback(window, key_callback);
+
     glfwMakeContextCurrent(window);
     gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
     glfwSwapInterval(1);
 
-    glfwSetKeyCallback(window, key_callback);
+    // NOTE: OpenGL error checks have been omitted for brevity
+
+    glGenBuffers(1, &vertex_buffer);
+    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
+
+    vertex_shader = glCreateShader(GL_VERTEX_SHADER);
+    glShaderSource(vertex_shader, 1, &vertex_shader_text, NULL);
+    glCompileShader(vertex_shader);
+
+    fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
+    glShaderSource(fragment_shader, 1, &fragment_shader_text, NULL);
+    glCompileShader(fragment_shader);
+
+    program = glCreateProgram();
+    glAttachShader(program, vertex_shader);
+    glAttachShader(program, fragment_shader);
+    glLinkProgram(program);
+
+    mvp_location = glGetUniformLocation(program, "MVP");
+    vpos_location = glGetAttribLocation(program, "vPos");
+    vcol_location = glGetAttribLocation(program, "vCol");
+
+    glEnableVertexAttribArray(vpos_location);
+    glVertexAttribPointer(vpos_location, 2, GL_FLOAT, GL_FALSE,
+                          sizeof(float) * 5, (void*) 0);
+    glEnableVertexAttribArray(vcol_location);
+    glVertexAttribPointer(vcol_location, 3, GL_FLOAT, GL_FALSE,
+                          sizeof(float) * 5, (void*) (sizeof(float) * 2));
 
     while (!glfwWindowShouldClose(window))
     {
         float ratio;
         int width, height;
+        mat4x4 m, p, mvp;
 
         glfwGetFramebufferSize(window, &width, &height);
         ratio = width / (float) height;
@@ -74,22 +141,14 @@ int main(void)
         glViewport(0, 0, width, height);
         glClear(GL_COLOR_BUFFER_BIT);
 
-        glMatrixMode(GL_PROJECTION);
-        glLoadIdentity();
-        glOrtho(-ratio, ratio, -1.f, 1.f, 1.f, -1.f);
-        glMatrixMode(GL_MODELVIEW);
+        mat4x4_identity(m);
+        mat4x4_rotate_Z(m, m, (float) glfwGetTime());
+        mat4x4_ortho(p, -ratio, ratio, -1.f, 1.f, 1.f, -1.f);
+        mat4x4_mul(mvp, p, m);
 
-        glLoadIdentity();
-        glRotatef((float) glfwGetTime() * 50.f, 0.f, 0.f, 1.f);
-
-        glBegin(GL_TRIANGLES);
-        glColor3f(1.f, 0.f, 0.f);
-        glVertex3f(-0.6f, -0.4f, 0.f);
-        glColor3f(0.f, 1.f, 0.f);
-        glVertex3f(0.6f, -0.4f, 0.f);
-        glColor3f(0.f, 0.f, 1.f);
-        glVertex3f(0.f, 0.6f, 0.f);
-        glEnd();
+        glUseProgram(program);
+        glUniformMatrix4fv(mvp_location, 1, GL_FALSE, (const GLfloat*) mvp);
+        glDrawArrays(GL_TRIANGLES, 0, 3);
 
         glfwSwapBuffers(window);
         glfwPollEvents();