surface buffer cardinality and outputs

[Jerome Glisse]

On Mon, Mar 18, 2013 at 4:17 PM, Bill Spitzak <spitzak at gmail.com> wrote:
> Jason Ekstrand wrote:
>
>>> For sub-pixel rendering the solution i have been thinking for a while
>>> but still haven't had time to prototype on weston, is to have weston
>>> send the transformation matrix to the client have the client render in
>>> screen coordinate space and when commiting its surface the client
>>> would also tell which transformation matrix it did use.
>
>
>> Yes, adding some support for that might be a good idea.  However, this
>> becomes a bit of an issue because the surface might not be rectangular
>> anymore or it might be rotated.  How do you recommend getting around
>> this?
>
>
> If the client ignores the transform sent from the compositor, then it will
> draw a rectangular image that fills the buffer it allocated.
>
> If the client uses the transform sent from the compositor then it will
> realize that it's rectangular image when transformed has a larger bounding
> box and will allocate a buffer of that size, clear the unused area, and draw
> the rotated rectangle.
>
> The client is going to have to be able to tell the compositor that the
> buffer image represents a surface of a given rectangular size with a given
> transform (the compositor cannot get the rectangle back from the buffer size
> and transform as there are many possible rectangles at the given angle that
> fill a given bounding box). This means this information must be separated
> from the buffer size.
>
> This will also allow a client to specify a subrectangle of the buffer as a
> surface, and (more importantly imho) specify that the buffer does not fill
> the surface, for instances where it knows the decorations are clipped off.
>

Yes this is the idea i had, the client render in screen space and send
to the server a possible bigger buffer than what its window need.
Client send the screen space buffer size (wdith & height) but also the
untransformed size (width and height) and the transformation matrix
that was use. You also need a rounding convention which in this case
should be ceil

All other information such as opaque region will be given untransformed.

Cheers,
Jerome