On Thu, 25 Jun 2020 19:01:33 +1000 Brad Robinson <brobin...@toptensoftware.com> wrote:
> That said, what would be the recommended way to implement this - would you > typically have one surface for the decorations and an embedded sub-surface > for the content area? eg: what happens if you use a drawing library > (cairo/skia whatever) for the decorations but then want to embed opengl > content for example. Hi, while it may be attractive to use one surface for your content and several (sub-)surfaces for the decorations, I believe it can cause "seams" to become visible if the compositor is doing anything else than showing the pixels 1:1, e.g. fractional scaling, zoom, tilted windows (a gimmick in Weston, freedom to arbitrarily rotate windows). It is hard to do bilinear sampling across multiple textures, so it is likely the adjacent edges of two surfaces are not blended perfectly by a compositor. Whether that actually disturbs users or not depends on what is being show and how. Maybe it's not a big concern. If you use one big surface for decorations behind the main content, you obviously waste the memory in the decorations buffer occluded by the main content. Hence piecing together decorations from four small surfaces. My personal opinion favours blitting decorations into the main surface. With OpenGL it's not a problem per se, but the toolkit API you expose might make it difficult if the premise is that the user can own "the full surface" with OpenGL directly. If your main content comes from a video decoder or a camera, it may be best to use sub-surface(s). Blitting into a video frame might not work too well. Not having to copy the video content is the main intended use case for sub-surfaces. Thanks, pq
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