gl.c

void initialiseGL() {
    const char *fragment = "                                   \
     varying vec2 v_texcoord;                                  \
     uniform sampler2D s_texture_y;                            \
     uniform sampler2D s_texture_u;                            \
     uniform sampler2D s_texture_v;                            \
     void main() {                                             \
         float y = texture2D(s_texture_y, v_texcoord).r;       \
         float u = texture2D(s_texture_u, v_texcoord).r - 0.5; \
         float v = texture2D(s_texture_v, v_texcoord).r - 0.5; \
                                                               \
                                                               \
         float r = y +             1.402 * v;                  \
         float g = y - 0.344 * u - 0.714 * v;                  \
         float b = y + 1.772 * u;                              \
                                                               \
         gl_FragColor = vec4(r,g,b,1.0);                       \
     }                                                         \
    ";

    const char *vertex = "                                     \
     attribute vec4 position;                                  \
     attribute vec2 texcoord;                                  \
     uniform mat4 modelViewProjectionMatrix;                   \
     varying vec2 v_texcoord;                                  \
                                                               \
     void main() {                                             \
         gl_Position = modelViewProjectionMatrix * position;   \
         v_texcoord = texcoord.xy;                             \
     }                                                         \
    ";

    GLint status, length;

    // Vertex shader
    shader.vertex = glCreateShader(GL_VERTEX_SHADER);
    length = strlen(vertex);
    glShaderSource(shader.vertex, 1, (const GLchar **)&vertex, &length);
    glCompileShader(shader.vertex);

    glGetShaderiv(shader.vertex, GL_COMPILE_STATUS, &status);

    if (!status) {
        GLsizei length; char message[5000];
        glGetShaderInfoLog(shader.vertex, 5000, &length, message);
        printf("%s\n", message);
        assert(false);
    }

    // Fragment shader
    shader.fragment = glCreateShader(GL_FRAGMENT_SHADER);
    length = strlen(fragment);
    glShaderSource(shader.fragment, 1, (const GLchar **)&fragment, &length);
    glCompileShader(shader.fragment);
    glGetShaderiv(shader.fragment, GL_COMPILE_STATUS, &status);
    if (!status) {
        GLsizei length; char message[5000];
        glGetShaderInfoLog(shader.fragment, 5000, &length, message);
        printf("%s\n", message);
        assert(false);
    }

    // Create program, attach both shaders and link
    shader.program = glCreateProgram();

    glAttachShader(shader.program, shader.vertex);
    glAttachShader(shader.program, shader.fragment);

    glBindAttribLocation(shader.program, ATTRIBUTE_VERTEX, "position");
    glBindAttribLocation(shader.program, ATTRIBUTE_TEXCOORD, "texcoord");

    glLinkProgram(shader.program);
    glGetProgramiv(shader.program, GL_LINK_STATUS, &status);
    if (!status) {
        GLsizei length; char message[5000];
        glGetProgramInfoLog(shader.program, 5000, &length, message);
        printf("%s\n", message);
        assert(false);
    }

    // Validate
    glValidateProgram(shader.program);
    glGetProgramiv(shader.program, GL_VALIDATE_STATUS, &status);
    if (!status) {
        GLsizei length; char message[5000];
        glGetProgramInfoLog(shader.program, 5000, &length, message);
        printf("%s\n", message);
        assert(false);
    }

    // Get the locations of the shader variables
    shader.matrix = glGetUniformLocation(shader.program, "modelViewProjectionMatrix");
    shader.textures[0] = glGetUniformLocation(shader.program, "s_texture_y");
    shader.textures[1] = glGetUniformLocation(shader.program, "s_texture_u");
    shader.textures[2] = glGetUniformLocation(shader.program, "s_texture_v");
}