Add basic GL drawing

main.cpp

@@ -1,11 +1,39 @@
 #include <cstdlib>
 
+#include <GL/glew.h>
 #include <GL/glfw.h>
 
 #include <emscripten/emscripten.h>
 
+static GLuint load_shader(GLenum type, const char *source);
+
+static GLuint vertex_shader;
+static GLuint fragment_shader;
+
+static GLuint program;
+
 static void iterate();
 
+static const char vertex_shader_source[] = \
+"attribute vec4 position;               \n"\
+
+"void main(void) {                      \n"\
+"  gl_Position = position;              \n"\
+"}                                      \n";
+
+static const char fragment_shader_source[] =   \
+"void main(void) {                          \n"\
+"  gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0); \n"\
+"}                                          \n";
+
+static const GLfloat triangle_vertices[] = {
+   0.0,  0.8, 0.0,
+  -0.8, -0.8, 0.0,
+   0.8, -0.8, 0.0,
+};
+
+static GLuint triangle;
+
 int main()
 {
   if (!glfwInit())
@@ -17,10 +45,49 @@ int main()
     exit(EXIT_FAILURE);
   }
 
-  emscripten_set_main_loop(iterate, 60, 1);
+  if (glewInit() != GLEW_OK)
+  {
+    glfwCloseWindow();
+    glfwTerminate();
+    exit(EXIT_FAILURE);
+  }
+
+  vertex_shader = load_shader(GL_VERTEX_SHADER, vertex_shader_source);
+  fragment_shader = load_shader(GL_FRAGMENT_SHADER, fragment_shader_source);
+
+  program = glCreateProgram();
+  glAttachShader(program, vertex_shader);
+  glAttachShader(program, fragment_shader);
+  glBindAttribLocation(program, 0, "position");
+  glLinkProgram(program);
+  glUseProgram(program);
+
+  glGenBuffers(1, &triangle);
+  glBindBuffer(GL_ARRAY_BUFFER, triangle);
+  glBufferData(GL_ARRAY_BUFFER, 3 * 7 * sizeof(GLfloat), triangle_vertices, GL_STATIC_DRAW);
+  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), reinterpret_cast<const GLvoid*>(0));
+  glEnableVertexAttribArray(0);
+
+  glViewport(0, 0, 640, 480);
+
+  glClearColor(0, 0, 0, 0);
+
+  emscripten_set_main_loop(iterate, 0, 1);
+}
+
+GLuint load_shader(const GLenum type, const char *source)
+{
+  const GLuint shader = glCreateShader(type);
+  glShaderSource(shader, 1, &source, nullptr);
+  glCompileShader(shader);
+  return shader;
 }
 
 void iterate()
 {
+  glClear(GL_COLOR_BUFFER_BIT);
+
+  glDrawArrays(GL_TRIANGLES, 0, 3);
+
   glfwPollEvents();
 }