[PATCH 0/5] Scanning out buffers with transformed outputs

[Pekka Paalanen]

On Tue, 27 Nov 2012 12:29:20 -0800
Bill Spitzak <spitzak at gmail.com> wrote:

> Ander Conselvan de Oliveira wrote:
> > Hi,
> > 
> > This series adds support for scanning out a fullscreen client buffer
> > when the output is rotated. A Wayland patch adds a request for setting
> > the buffer transform, which the compositor handles by changing the
> > texture coordinates when compositing. If possible, the drm compositor
> > will scan out the client buffer.
> 
> Could the client provide an *arbitrary* transform that it used to create 
> the image in the buffer?
> 
> What the compositor does is multiply the inverse of this transform by 
> the transform it wants to use to put it on the screen to get the actual 
> transform from the source buffer to the outputs. There would also be an 
> api by which the compositor tells the client what transform it plans to 
> apply. The client could ignore this, or use it to render a new version 
> of the image.
> 
> I think there will be clients that can draw their own thumbnail images 
> much better than the scaled full-size image, especially due to correct 
> subpixel antialiasing, which is the reason you are communicating the 
> rotation to the clients now.

No, that is not the main reason. The reason is to be able to directly
scan out client surfaces, as full-screen or in an overlay plane.

Limiting to that main purpose, your other points do not seem
applicable. I'm not aware of any hardware that can scan out "arbitrary"
transformations without compositing first.


Thanks,
pq