[cairo] [Fwd: CAIRO_OPERATOR_SOURCE issue]

[Carl Banks]

Hello list.  Here's a little code to demonstrate an issue I'm having.


#include <stdio.h>
#include <cairo.h>

int main(void) {
     cairo_t *cr;
     cairo_surface_t *surface;
     unsigned char *data;

     surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,1,1);
     cr = cairo_create(surface);
     cairo_set_operator(cr,CAIRO_OPERATOR_SOURCE);
     cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 0.2);
     cairo_paint(cr);
     cairo_destroy(cr);

     data = cairo_image_surface_get_data(surface);

     printf("Cairo version: %s\n",cairo_version_string());
     printf("Color: (%d,%d,%d,%d)\n",data[1],data[2],data[3],data[0]);
}


I get the following output:

Cairo version: 1.8.10
Color: (51,51,51,51)


But I expect this output:

Cairo version: 1.8.10
Color: (255,255,255,51)


What's wrong: Cairo, my usage, or my understanding of
CAIRO_OPERATOR_SOURCE?  If it's the latter, how can I initialize a
surface to something like (255,255,255,51)?

It's not helpful to work around it by manipulating data directly,
because my real use case involves more complex rendering.

Thanks.


Carl Banks