[cairo] OPERATOR_SRC and no input

[Owen Taylor]

On Sun, 2005-01-09 at 13:33 +0100, Stefan Krause wrote:
> When I'm rendering a path that doesn't fill its bounding box completely 
> the image and xrender backend produces different output than the glitz 
> backend, e.g:
> 
> // fill background with white color
>   cairo_set_rgb_color (cr, 1.0, 1.0, 1.0);
>   cairo_set_alpha (cr, 1.0);
>   cairo_set_operator (cr, CAIRO_OPERATOR_SRC);
>   cairo_rectangle (cr, 0, 0, w, h);
>   cairo_fill (cr);
> 
> // now paint my path
>   cairo_set_operator (cr, CAIRO_OPERATOR_SRC);
>   cairo_set_alpha (cr, 1.0);
>   cairo_set_rgb_color (cr, 1.0, 0.0, 1.0);
>   cairo_move_to (cr, 100, 0);
>   cairo_line_to (cr, 200, 100);
>   cairo_line_to (cr, 100, 200);
>   cairo_line_to (cr, 0, 100);
>   cairo_close_path(cr);
>   cairo_fill(cr);
> 
> This will fill a path in a purple color and lets the background shine 
> through for the glitz backend. For the image and xrender backend the 
> bounding box of the path is filled black. I'd say glitz interpretation 
> of "no input" is correct, but you'll certainly know the Porter and Duff 
> rules better than I do.

What actually *should* have happened is for the entire surface to be
filled with black except for the path. The appearance of the bounding
box is a bug. Though that probably wasn't what you were looking for.

See the recent discussion on "non-clipping clips" for a lot more detail
on problems with operators like SRC.

Regards,
					Owen

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