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

[Bill Spitzak]

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.