#include <stdio.h>
#include <GL/glew.h>
#include <GL/gl.h>
#include <GL/glx.h>

static const char *vertex_shader_text =
"#version 120\n"
"#extension GL_ARB_texture_rectangle : require\n"
"uniform ivec2 tex_offset[8];\n"
"uniform sampler2DRect input_texture[8];\n"
"uniform int input_count;\n"
"uniform ivec2 frame_size;\n"
"uniform ivec2 frame_offset;\n"
"attribute vec2 position;\n"
"varying vec2 tex_coord[8];\n"
"varying vec2 frame_coord;\n"
"\n"
"void main() {\n"
"    gl_Position = vec4(position * vec2(2.0, 2.0) + vec2(-1.0, -1.0), 0.0, 1.0);\n"
"    frame_coord = position * vec2(frame_size) + frame_offset;\n"
"\n"
"    for( int i = 0; i < input_count; i++ ) {\n"
"        tex_coord[i] = position * vec2(frame_size) + frame_offset + tex_offset[i];\n"
"    }\n"
"}\n";

static const char *gain_offset_shader_text =
"#version 120\n"
"#extension GL_ARB_texture_rectangle : enable\n"
"uniform sampler2DRect input_texture[8];\n"
"varying vec2 tex_coord[8];\n"
"uniform float gain, offset;"
""
"void main() {"
"    vec4 color = texture2DRect( input_texture[0], tex_coord[0] );"
""
"    gl_FragColor = color * vec4(gain, gain, gain, 1.0)"
"        + vec4(offset, offset, offset, 0.0);"
"}";

int
main( int argc, char *argv[]) {
    Display *display;
    int fb_attrs[] = {
        GLX_DRAWABLE_TYPE, GLX_PBUFFER_BIT, None };
    int pbuf_attrs[] = { GLX_PBUFFER_WIDTH, 8, GLX_PBUFFER_HEIGHT, 8, GLX_PRESERVED_CONTENTS, False, None };
    int config_count = 0;
    GLXFBConfig *configs;
    GLXContext new_context;
    GLXPbuffer pbuf;

    printf( "Opening X display...\n" );
    display = XOpenDisplay( NULL );

    if( !display ) {
        printf( "Could not open X display.\n" );
        return -1;
    }

    printf( "Choosing framebuffer config\n" );
    configs = glXChooseFBConfig(
        display, DefaultScreen( display ), fb_attrs, &config_count );

    if( !config_count ) {
        printf( "No frame buffer configurations available. Which is weird.\n" );
        return -1;
    }

    new_context = glXCreateNewContext(
        display, configs[0], GLX_RGBA_TYPE, NULL, True );

    if( !new_context ) {
        printf( "Failed to create context.\n" );
        return -1;
    }

    pbuf = glXCreatePbuffer( display, configs[0], pbuf_attrs );

    if( pbuf == None ) {
        printf( "Failed to create XGL pixel buffer.\n" );
        return -1;
    }

    if( !glXMakeContextCurrent( display,
        pbuf,
        pbuf,
        new_context ) ) {
        printf( "Failed to set context current.\n" );
        return -1;
    }

    glewInit();

    GLuint vbuf;
    glGenBuffers( 1, &vbuf );

    float positions[] = {
        0.0f, 0.0f,
        1.0f, 0.0f,
        1.0f, 1.0f,
        0.0f, 1.0f
    };

    glBindBuffer( GL_ARRAY_BUFFER, vbuf );
    glBufferData( GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW );

    GLuint vshader = glCreateShader( GL_VERTEX_SHADER );
    glShaderSource( vshader, 1, &vertex_shader_text, NULL );
    glCompileShader( vshader );

    GLuint fshader = glCreateShader( GL_FRAGMENT_SHADER );
    glShaderSource( fshader, 1, &gain_offset_shader_text, NULL );
    glCompileShader( fshader );

    GLuint program = glCreateProgram();
    glAttachShader( program, vshader );
    glAttachShader( program, fshader );
    glLinkProgram( program );

    glUseProgram( program );

    GLuint position_attribute = glGetAttribLocation( program, "position" );

    glEnableVertexAttribArray( position_attribute );
    glVertexAttribPointer( position_attribute, 2, GL_FLOAT, GL_FALSE, 0, 0 );

    glDrawArrays( GL_TRIANGLE_FAN, 0, 4 );

    glXDestroyPbuffer( display, pbuf );
    glXDestroyContext( display, new_context );
    printf( "Success\n" );
    return 0;
}