Float images loaded in Blender are converted to scene linear and don't
require additional conversion. Image engine can reuse the rect_float of
those images. An assert statement is added tp make this more clear and
to test on missing code paths or future developments.
Image engine is used to draw the image inside the image editor, uv editor and node editor. The
performance during scrolling wasn't smooth when using larger textures on a dedicated GPU. Main
reason was the data transfers that happens when panning the image.
The original idea of the image engine was to have 4 textures that are as large as the editor.
Those textures would be used to simulate a larger canvas where if the texture is out of the
visible area the texture would be reused to contain the data of a new visible area. This would
reduce the data transfers to only on certain x/y coordinates. Between those coordinates no
data transfers would be needed.
This patch implements the mechanism described above. During development other areas to
improve have been detected (incorrect color management for float textures, using different
image formats to reduce data transfer bandwidths, using different render techniques for
images upto 8k). More improvements will follow.
Previously we used to cache a float image representation of the image in
rect_float. This adds some incorrect behavior as many areas only expect
one of these buffers to be used.
This patch stores float buffers inside the image engine. This is done per
instance. In the future we should consider making a global cache.
