draw triangle following tutorial

cpp/experiments/link_glew_sdl/main.cpp

@@ -1,7 +1,121 @@
+// ----------------------------------------------------------------------------
+// This file contains source code from the following tutorial:
+// https://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Introduction
+// ----------------------------------------------------------------------------
+
+#include <cstdlib>
 #include <iostream>
 
-int main() {
-  std::cout << "Link GLEW & SDL\n";
+#include "deps/GLEW-2.2.0/include/GL/glew.h"
+#include "deps/SDL2-2.26.2/include/SDL.h"
+
+GLuint program;
+GLuint attribute_coord2d;
+
+bool init_resources() {
+  GLint compile_ok = GL_FALSE;
+  GLint link_ok = GL_FALSE;
+
+  // Colors
+  GLuint vs = glCreateShader(GL_VERTEX_SHADER);
+  const char* vs_source =
+      "#version 120\n"
+      "attribute vec2 coord2d;                  "
+      "void main(void) {                        "
+      "  gl_Position = vec4(coord2d, 0.0, 1.0); "
+      "}";
+  glShaderSource(vs, 1, &vs_source, NULL);
+  glCompileShader(vs);
+  glGetShaderiv(vs, GL_COMPILE_STATUS, &compile_ok);
+  if (!compile_ok) {
+    std::cerr << "Error in vertex shader\n";
+    return false;
+  }
+
+  // Pixels
+  GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
+  const char* fs_source =
+      "#version 120\n"
+      "void main(void) {        "
+      "  gl_FragColor[0] = 0.0; "
+      "  gl_FragColor[1] = 0.0; "
+      "  gl_FragColor[2] = 1.0; "
+      "}";
+  glShaderSource(fs, 1, &fs_source, NULL);
+  glCompileShader(fs);
+  glGetShaderiv(fs, GL_COMPILE_STATUS, &compile_ok);
+  if (!compile_ok) {
+    std::cerr << "Error in fragment shader\n";
+    return false;
+  }
+
+  // Link shaders with program
+  program = glCreateProgram();
+  glAttachShader(program, vs);
+  glAttachShader(program, fs);
+  glLinkProgram(program);
+  glGetProgramiv(program, GL_LINK_STATUS, &link_ok);
+  if (!link_ok) {
+    std::cerr << "Error in glLinkProgram\n";
+    return false;
+  }
+
+  return true;
+}
+
+void render(SDL_Window* window) {
+  glClearColor(1.0, 1.0, 1.0, 1.0);
+  glClear(GL_COLOR_BUFFER_BIT);
+
+  glUseProgram(program);
+
+  glEnableVertexAttribArray(attribute_coord2d);
+  GLfloat triangle[]{.0, .8, -.8, -.8, .8, -.8};
+  glVertexAttribPointer(attribute_coord2d, 2, GL_FLOAT, GL_FALSE, 0, triangle);
+  glDrawArrays(GL_TRIANGLES, 0, 3);
+  glDisableVertexAttribArray(attribute_coord2d);
+
+  SDL_GL_SwapWindow(window);
+}
+
+void main_loop(SDL_Window* window) {
+  while (true) {
+    SDL_Event event;
+
+    while (SDL_PollEvent(&event)) {
+      if (event.type == SDL_QUIT) {
+        return;
+      }
+    }
+
+    render(window);
+  }
+}
+
+void free_resources() {
+  // ...
+}
+
+int main(int argv, char** args) {
+  SDL_Init(SDL_INIT_VIDEO);
+  SDL_Window* window = SDL_CreateWindow(
+      "My First Triangle", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640,
+      480, SDL_WINDOW_RESIZABLE | SDL_WINDOW_OPENGL);
+  SDL_GL_CreateContext(window);
+
+  GLenum glew_status = glewInit();
+  if (glew_status != GLEW_OK) {
+    std::cerr << "Error: glewInit " << glewGetErrorString(glew_status);
+    return EXIT_FAILURE;
+  }
+
+  if (!init_resources()) {
+    return EXIT_FAILURE;
+  }
+
+  main_loop(window);
+
+  free_resources();
 
-  return 0;
+  return EXIT_SUCCESS;
 }