draw with OpenGL3 using a shader

box.f.glsl

@@ -0,0 +1,6 @@
+uniform vec4 color;
+
+void main(void)
+{
+    gl_FragColor = color;
+}

box.v.glsl

@@ -0,0 +1,9 @@
+uniform float size;
+uniform vec2 position;
+
+attribute vec2 coord;
+
+void main(void)
+{
+    gl_Position = vec4(position + size * coord, 0, 1);
+}

sdl-game-controller.cc

@@ -1,41 +1,78 @@
 #include <SDL.h>
-#include <GL/gl.h>
-#include <GL/glu.h>
+#include "glcxx.hpp"
+#include "GL3/gl3w.h"
+#include <iostream>
 #include <stdio.h>
 
-#define WIDTH   500
-#define HEIGHT  500
+using namespace std;
 
-void init(void)
+#define WIDTH   800
+#define HEIGHT  800
+
+std::shared_ptr<glcxx::Program> program;
+std::shared_ptr<glcxx::Buffer> box_buffer;
+std::shared_ptr<glcxx::Array> box_array;
+static struct
+{
+    GLint size;
+    GLint color;
+    GLint position;
+} uniforms;
+int color = 0;
+GLfloat size = 0.2;
+GLfloat position[2] = {0.0, 0.0};
+GLfloat colors[][4] = {
+    {1.0, 0.7, 0.0, 1.0},
+    {0.0, 0.5, 1.0, 1.0},
+    {1.0, 1.0, 0.0, 1.0},
+    {0.2, 0.2, 1.0, 1.0},
+};
+
+bool init(void)
 {
     glClearColor (0.0, 0.0, 0.0, 0.0);
-    glEnable(GL_DEPTH_TEST);
-    glShadeModel(GL_FLAT);
     glViewport(0, 0, WIDTH, HEIGHT);
-    glMatrixMode(GL_PROJECTION);
-    glLoadIdentity();
-    glOrtho(-0.5, WIDTH - 0.5, -0.5, HEIGHT - 0.5, -1, 1);
-    glMatrixMode(GL_MODELVIEW);
-    glLoadIdentity();
+    try
+    {
+        program = glcxx::Program::create(
+            glcxx::Shader::create_from_file(GL_VERTEX_SHADER, "box.v.glsl"),
+            glcxx::Shader::create_from_file(GL_FRAGMENT_SHADER, "box.f.glsl"),
+            "coord", 0);
+        uniforms.size = program->get_uniform_location("size");
+        uniforms.color = program->get_uniform_location("color");
+        uniforms.position = program->get_uniform_location("position");
+
+        box_buffer = glcxx::Buffer::create(GL_ARRAY_BUFFER, GL_STATIC_DRAW,
+                                            {-1.0, -1.0,
+                                             1.0, -1.0,
+                                             1.0, 1.0,
+                                             -1.0, 1.0});
+        box_array = glcxx::Array::create();
+        box_array->bind();
+        box_buffer->bind();
+        glEnableVertexAttribArray(0);
+        glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE,
+                2 * sizeof(GLfloat), NULL);
+    }
+    catch (glcxx::Error & e)
+    {
+        cerr << "glcxx error: " << e.what() << endl;
+        return false;
+    }
+    return true;
 }
 
 void display(SDL_Window * window)
 {
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
-    glColor3f(1, 1, 1);
-    glBegin(GL_QUADS);
-        glVertex3f(10, HEIGHT / 2, 0.0);
-        glVertex3f(10, 3 * HEIGHT / 4, 0.0);
-        glVertex3f(WIDTH / 2, 3 * HEIGHT / 4, 0.0);
-        glVertex3f(WIDTH / 2, HEIGHT / 2, 0.0);
-    glEnd();
-    glColor3f(1, 0.6, 0);
-    glBegin(GL_LINE_LOOP);
-        glVertex2f(0, 0);
-        glVertex2f(WIDTH - 1, 0);
-        glVertex2f(WIDTH - 1, HEIGHT - 1);
-        glVertex2f(0, HEIGHT - 1);
-    glEnd();
+
+    program->use();
+    box_array->bind();
+    glUniform4fv(uniforms.color, 1, colors[color]);
+    glUniform2fv(uniforms.position, 1, position);
+    glUniform1f(uniforms.size, size);
+    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
+
     SDL_GL_SwapWindow(window);
 }
 
@@ -62,9 +99,25 @@ int main(int argc, char *argv[])
         return 2;
     }
 
-    SDL_GLContext gl_context = SDL_GL_CreateContext(window);
+    (void)SDL_GL_CreateContext(window);
+
+    if (gl3wInit())
+    {
+        cerr << "Failed to initialize GL3W" << endl;
+        return 2;
+    }
+
+    if (!gl3wIsSupported(3, 0))
+    {
+        cerr << "OpenGL 3.0 is not supported!" << endl;
+        return 2;
+    }
+
+    if (!init())
+    {
+        return 2;
+    }
 
-    init();
     display(window);
     SDL_Event event;
     while (SDL_WaitEvent(&event))