The new field ImageOp.Rect is initialized to cover the entire source
image, but can be modified to draw only a section of it.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Remembering the order of the corners in the RoundRect is difficult,
which suggest that RoundRect should be a struct with named fields.
Do that, and make Rect the special case where corner radii are all
zero.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
With public ImageOp fields there was no way to mark an image.Image as modified.
Replace them with NewImageOp that always make a copy, and use the opportunity
to ensure the copy is ready to upload to a GPU texture.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Elias Naur