ccairo

Cairo clip region existing of multiple rectangles?

I need a clip region that exists of a several (possibly overlapping) rectangles, but can't figure out how to create one with cairo.

Since there is a

cairo_rectangle_list_t *
cairo_copy_clip_rectangle_list (cairo_t *cr);

I assumed that the clip region CAN exist of more than one rectangle (if not, then this wouldn't return a list of rectangles...)

Moreover, cairo_rectangle_list_t exists - surely I can create a list of rectangles myself then... and create the clip region from that?

But how?

Solution

  • Just create a path that consists of several rectangles and clip with it. Here is an example with two overlapping rectangles, but it works just as well with more.

    Result of the following C program

    #include <cairo.h>

int main() {
    cairo_surface_t *s = cairo_image_surface_create(CAIRO_FORMAT_RGB24, 100, 100);
    cairo_t *cr = cairo_create(s);

    cairo_set_source_rgb(cr, 1, 1, 1);

    cairo_rectangle(cr, 10, 10, 50, 50);
    cairo_rectangle(cr, 40, 40, 50, 50);
    cairo_clip(cr);
    cairo_paint(cr);

    cairo_surface_write_to_png(s, "out.png");
    cairo_destroy(cr);
    cairo_surface_destroy(s);
    return 0;
}