Improve rendering performance

The current image rendering is rather slow, causing some nasty tearing, i.e. when moving windows or streaming video. Other spice clients do much better, so I think there is potential to improve the client side rendering.

I found the usage of putImageData in display.js, which is rather slow. I think it can be replaced with drawImage, but that would require a correct format, likely needs changes to the convert_spice_bitmap_to_web function in bitmap.js.

Anyone brave enough to send a PR for this transition? Or other ideas how to improve the rendering performance to allow smooth video streaming over the spice client?

It's not clear the request. Do you want to hire somebody to code that change?

My intention was to improve the performance issue, but it turned out to be quite involved. So I decided to document the problem description and minor findings that occurred to me with this issue.

I am looking for ideas how to make rendering faster. If you have knowledge, please share proposals.

If you have time for sending a PR, that would be even more appreciated.