makeRasterImage() needed whether CPU or GPU rendering

[sstillwell]

There appears to be an especially-large performance hit on GPU if controls overlap on screen.

Here are some instructions for a good PR

• create an issue first to outline the problem, to reference in this PR
  This PR fixes problem described in makeRasterImage() needed in GPU as well as CPU when drawing Bitmap #955
• clearly describe the problem that the PR fixes
  Performance is impacted when drawing bitmaps, especially controls with bitmap stacks, and even more especially if controls overlap (with associated extra draws/redraws)
• each PR should address one thing. It can include multiple commits, but you should try and tidy up work done into logical units if possible.
  This is the smallest possible PR to address this bug - we literally just stop conditionally rasterizing only for CPU rendering.
• pay attention to iplug2 coding style
• If it applies to an option e.g. IGRAPHICS_NANOVG or VST3 plug-ins, try to provide fixes for all options (e.g. all graphics backends or all plug-in formats)

If you follow these rules, it is more likely we will consider your PR, but please don't be upset if we decide we don't want to merge your work.

thanks, we like PRs!

oli & alex

[sstillwell]

I'm not sure why all this would have failed...it looks like code download failed in a couple of places, so maybe build failed due to missing files? Certainly the change in the PR is trivial and is working successfully in my local GitLab repo.

[olilarkin]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[olilarkin]

So the reason I haven't merged this yet is because I would have thought that keeping bitmaps on the GPU would be a performance win. Need to investigate more

[sstillwell]

Please do - the difference in performance is not small in our experience.