Ipu device on i.mx6 can combine video and UI, then show to frame buffer. It is different with video and graphics blending on DP, which uses 2 frame buffer as FG and BG.
When combine with ipu device, input video is resized to output resolution, and overlay size is same as output, so we see video and UI, combined together with global alpha or local alpha, are always the same size…
If we want a small video window overlay on UI, how to deal with? Here is a propose:
1. When allocate buffer, request a larger input buffer.
2. Fill special area of input buffer with input video.
3. Fill overlay buffer with UI.
4. Fill alpha buffer with local alpha value, transparent on video region while opaque on other region.
You can check overlay effect in attached picture.