Introduce a render cache that keeps the result of scaling, color
management, display filters and shell mask (for tools like fuzzy
select).
Change gimpdisplayshell-render.[ch] to only render to the cache and
manage a cairo region of the cache's valid area. Call cache
invalidation functions form various places. Change the API of all
render functions to be in display coordinates.
Also get rid of gimpdisplayxfer.[ch] because we now have a
canvas-sized cairo surface which is a surface similar to the
destination surface.
... not screen space
Flip and rotate the canvas around the center of the viewport,
instead of the center of the image. Scroll the display as
necessary to keep the center of the viewport fixed during
these operations. This applies to both the corresponding
menu items, and rotation using Shift+Space.
Likewise, flip the canvas across the designated axis in
screen space, instead of image space. Rotate the display as
necessary, such that the reflection appears to happen in
screen space, regardless of the current rotation angle of the
canvas.
Added complete API for zoom/unzoom (scale and scroll) and
rotate/unrotate, with the same set of functions as the existing
transform/untransform. Moved some special case functions to the
namespaces they belong.
First version of display rotation, inspired by gimp-painter.
The rotation always happens around the image's center.
The only "UI" for rotating is currently shift+middle-drag and
shift+space-drag. Control constrains the angle to 15 degrees
and is currently the only way to go back to "no rotation".
Ell