#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include <GL/glut.h>

#define countof(x) (sizeof(x) / sizeof(*(x)))

const char *vshader[] =
{
    "attribute vec2 aCoord;\n",
    "void main(void)\n",
    "{\n",
    "    gl_Position = vec4(aCoord.x / 128.0 - 1.0, aCoord.y / 128.0 - 1.0, 0.0, 1.0);\n",
    "}\n",
};
const char *fshader[] =
{
    "void main(void)\n",
    "{\n",
    "    gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);\n",
    "}\n",
};

int g_shader;

struct Vertex
{
    unsigned char x, y;
    //Add some dummy bytes to make the stride non-zero.
    unsigned char dummy[2];
};
struct Vertex star[] =
{
    {250, 125},
    {23, 198},
    {163, 6},
    {163, 243},
    {23, 51},
    {250, 125},
};

void Init()
{
    int i;
    //Fill the dummy bytes with random data to make obvious if they are read
    for (i = 0; i < countof(star); ++i)
    {
        star[i].dummy[0] = rand() & 0xFF;
        star[i].dummy[1] = rand() & 0xFF;
    }
    glewInit();

    int vsh = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vsh, countof(vshader), vshader, NULL);
    glCompileShader(vsh);

    int fsh = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fsh, countof(fshader), fshader, NULL);
    glCompileShader(fsh);

    g_shader = glCreateProgram();
    glAttachShader(g_shader, vsh);
    glAttachShader(g_shader, fsh);
    glLinkProgram(g_shader);

    glBindAttribLocation(g_shader, 0, "aCoord");
}

void OnDisplay(void)
{
    glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(g_shader);

    glEnableVertexAttribArray(0);

    glVertexAttribPointer(0, 2, GL_UNSIGNED_BYTE, GL_FALSE, sizeof(struct Vertex), star);
    glDrawArrays(GL_LINE_STRIP, 0, countof(star));
    glDisableVertexAttribArray(0);

    glUseProgram(0);

    GLuint error;
    while ((error = glGetError()) != 0)
        printf("GLError 0x%04X\n", error);

    glutSwapBuffers();
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutCreateWindow("Test");
    Init();
    glutDisplayFunc(OnDisplay);

    glutMainLoop();
    return 0;
}