Re: New drawing/scrolling model

[Paul Davis <paul linuxaudiosystems com>]

On Thu, May 2, 2013 at 6:03 PM, Søren Sandmann <sandmann cs au dk> wrote:

Alexander Larsson <alexl redhat com> writes:

> * Try a tile-based approach for GtkPixelCache to avoid having
>   to do a same-surface copy (usign an intermediate surface) when
>   scrolling the cache.

An alternative to tiles is to keep track of an origin within the
surface:

        +--------+--------------------------+
        | Bot R  | Bottom left              |
        |        |                          |
        +--------O--------------------------+
        | Top R  | Top left                 |
        |        |                          |
        |        |                          |
        |        |                          |
        |        |                          |
        |        |                          |
        |        |                          |
        |        |                          |
        +--------+--------------------------+

with the contents of the surface addressed modulo width and
height. Scrolling is then just a matter of moving that origin, but
copying from the surface may require four separate blits. Similarly,
rendering to some rectangle may have to be split into four separate
operations.

this is where trying to be too generic hurts.

a given widget knows its aspect ratio. for things that are short and wide, their "pixel cache" will consist of a set of full-height, partial-width surfaces.
for things that are tall and narrow, their "pixel cache" will consist of a set of full-width, partial-height caches. for things that are short and narrow, their cache will consist of a single surface. for things that are wide and tall ... well, they're on their own ...