[Pixman] Source clipping: how-to and tests

Bill Spitzak spitzak at gmail.com
Tue Mar 3 14:04:22 PST 2015

For Wayland you can easily make another shm buffer out of a subrectangle 
of an existing one by using the appropriate stride.

I don't know if this can be done with egl.

Because pixman is already dealing with stride, it certainly should be 
technically possible to deal with an arbitrary rectangle clipped out of 
the source image. The api to make a new pixman_image_t seems like the 
right approach because it is by defnintion only a rectangle.

On 03/03/2015 05:36 AM, Pekka Paalanen wrote:
> On Tue, 3 Mar 2015 13:47:22 +0100
> Petr Kobalíček <kobalicek.petr at gmail.com> wrote:
>> Hi Pekka,
>> Can't be this solved by creating a subimage based on the input image and
>> the viewport? This way you can basically use the same pipeline. I'm not
>> sure, however, if I fully understand the issue.
> Hi,
> that's what Siarhei suggested below. It seems to work too, I just got
> it implemented.
> Thanks,
> pq
>> On Tue, Mar 3, 2015 at 8:49 AM, Pekka Paalanen <ppaalanen at gmail.com> wrote:
>>> On Mon, 2 Mar 2015 17:33:16 +0200
>>> Siarhei Siamashka <siarhei.siamashka at gmail.com> wrote:
>>>> In some cases, the source image clipping might be simulated by
>>>> just wrapping a rectangular area of an existing image as a new
>>>> pixman_image_t. And then using it as the source image in the
>>>> compositing operation.
>>> That's an excellent idea! I will try that.
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