[cairo] crasher

[Øyvind Kolås]

On Sat, 19 Mar 2005 19:02:09 -0500, John McCutchan <ttb at tentacle.dhs.org> wrote:
> Yo,
> 
> This simple program crashes cairo. Am I doing something wrong or what?

>  /* snip */
>         while (1)       {
>                         cairo_scale (cr, 400, 16);
>                         cairo_set_line_width (cr, 0.04);
>                         cairo_move_to (cr, 0.0, 0.0);
>  /* snip */
>                         cairo_close_path (cr);
>                         cairo_stroke (cr);
>         }
> /* snip */

The reason this program crashes is that you are zooming in 400% , 16%
for each iteration, if your intention is just to repeatedly draw the
same figure, you would have to add a cairo_save(cr);
cairo_restore(cr); pair around the drawing commands.

/***********/

#include <cairo.h>
#include <stdlib.h>

int main (int argc, char **argv)
{
       int x, y, stride;
       cairo_t *cr;

       x = 400;
       y = 400;
       stride = x * 4;

       cr = cairo_create ();
       cairo_set_target_image (cr, (char *)malloc (sizeof(uint32_t) * x
* y), CAIRO_FORMAT_ARGB32, x, y, stride);

       while (1)       {
                       cairo_save (cr); /*< added */
                       cairo_scale (cr, 400, 16);
                       cairo_set_line_width (cr, 0.04);
                       cairo_move_to (cr, 0.0, 0.0);
                       cairo_line_to (cr, 1.0, 0.0);
                       cairo_line_to (cr, 1.0, 1.0);
                       cairo_line_to (cr, 0.0, 1.0);

                       cairo_save (cr);
                               cairo_set_rgb_color (cr, 0.3725, 0.5254,
0.7019);
                               cairo_fill (cr);
                       cairo_restore (cr);

                       cairo_close_path (cr);
                       cairo_stroke (cr);
                       cairo_restore (cr); /*< added */
       }
}


/***********/

That program will happily run forever, and not fail due to allocation
of large amounts of temporary memory to create shapes many times
larger than the allocated buffer.

/Øyvind K.

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