[gs-devel] Understanding clamp_pattern_bbox()

[Kevin Shanahan]

On Tue, May 01, 2007 at 07:36:50PM +0400, Leonardo wrote:
> >    /*
> >     * Check if the pattern bounding box intersects the page.
> >     */
> >    xlower = (xdev + pbbox->p.x > 0) ? pbbox->p.x : -xdev;
> >    xupper = (xdev + pbbox->q.x < width) ? pbbox->q.x : -xdev + width;
> >    ylower = (ydev + pbbox->p.y > 0) ? pbbox->p.y : -ydev;
> >    yupper = (ydev + pbbox->q.y < height) ? pbbox->q.y : -ydev + height;
> >
> >I wonder if someone could spell out for me the logic behind these
> >calculations?
> 
> It looks as a superposition of 2 operations :
> 
> 1. Intersect xdev + pbbox and [0:width][0:height].
> 2. Shift coords to [-xdev, -ydev].

Ah, thanks - I can see it now. However, I still think there might be a
bug lurking here somewhere. Am I right to understand that when the
function exists the following should be true:

     pbbox->q.x - pbbox->p.x <= width
  && pbbox->q.y - pbbox->p.y <= height

In this instance I have:

  (gdb) print width
  $2 = 2479
  (gdb) print height
  $3 = 3508

And, at function exit:

  (gdb) print *pbbox
  $5 = {p = {x = 155.63597106933594, y = -6677.2569427490234}, q = {x = 117745.96476745605, y = 380.97372436523438}}

Regards,
Kevin.