That should be about 360MB of uncompressed data (1024x768x88x4 bytes) which should fit into the memory of most IGPs, which generally reserve 1 or 2 GB. Compositing 4 images at once should be something that even a very old GPU should have no problems with, even at 4K resolution. Windows Desktop Composition probably does a lot more work.

Still this indeed gets my laptop's fans spinning in both Chrome and Firefox. I wonder why that is... I don't think you can do a lot wrong code wise here. Maybe the composition takes a software path, but why?