20141222 :: GrayScale (OpenGL)

void grayScale() {
    if (fst) {
        fst = false;
        glReadPixels(0, 0, Width, Height, GL_RGBA, GL_UNSIGNED_BYTE, pixelData);
        uint count = Width * Height;
        for (uint i = 0; i < count; ++i) {
            double luminance = 0.3 * pixelData[i * 4] + 0.59 * pixelData[i * 4 + 1] + 0.11 * pixelData[i * 4 + 2];
            pixelData[i] = static_cast<uchar>(luminance);
        }
    }
    glDrawPixels(Width, Height, GL_LUMINANCE, GL_UNSIGNED_BYTE, pixelData);
}