Making a screenshot using Xlib and Cairo libs [fail]

Question

I\'m trying to make a screenshot using Xlib and Cairo, however I\'m not sure to do it the good way, \"stride\" is really confusing me.

Answer 1

TFM:

CAIRO_FORMAT_RGB24
    each pixel is a 32-bit quantity, with the upper 8 bits unused

TFM:

stride = cairo_format_stride_for_width (format, width);
data = malloc (stride * height);

Hence, the correct index calculation is

data[y * stride + x * 4 + 0] = blue;
data[y * stride + x * 4 + 1] = green;
data[y * stride + x * 4 + 2] = red;    /* yes, in this order */

Also, masks are taken from the image and shifts are hard-coded, which makes absolutely no sense. Calculate the shifts from the masks.