Use Matrix4 for viewProjection to allow for 3D UI

[Squareys]

Hi @mosra !

As discussed, I changed all the Matrix3 projection matrices to Matrix4 to allow for arbitrary transforms of UserInterfaces. I also added AbstractUserInterface::setViewProjectionMatrix. We should question whether this is the right approach. As far as I see, this does not allow separating planes from each other yet, hence, having a single UserInterface with multiple panels with their own 3D transformations each. Will look into that soon, though.

Thanks in advance!

Cheers, Jonathan.

[codecov-io]

Codecov Report

Merging #3 into master will not change coverage. The diff coverage is 14.28%.

@@           Coverage Diff           @@
##           master       #3   +/-   ##
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  Coverage   19.24%   19.24%           
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  Files          35       35           
  Lines        1408     1408           
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  Hits          271      271           
  Misses       1137     1137

Impacted Files	Coverage Δ
src/Magnum/Ui/BasicUserInterface.h	100% <ø> (ø)	:arrow_up:
src/Magnum/Ui/BasicPlane.hpp	21.05% <0%> (ø)	:arrow_up:
src/Magnum/Ui/AbstractUiShader.h	0% <0%> (ø)	:arrow_up:
src/Magnum/Ui/BasicPlane.h	91.66% <0%> (ø)	:arrow_up:
src/Magnum/Ui/BasicUserInterface.hpp	10% <0%> (ø)	:arrow_up:
src/Magnum/Ui/BasicUserInterface.cpp	23.33% <100%> (ø)	:arrow_up:

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[mosra]

Some thoughts on this:

• the Ui::Plane only purpose was to organize things for a correct back-to-front rendering, i never thought about anything else (until now!)
• your proposal for 3D rendering (each plane on a different location in 3D) could be also extended for rendering to different windows in 2D, for example
• so maybe it would make more sense to have the projection matrix per-plane instead of per-ui?
• did you measure perf difference compared to using mat3? i wonder how much impact it has

[Squareys]

could be also extended for rendering to different windows in 2D, for example

Yes! Different locations is basically different windows, good point.

projection matrix per-plane instead of per-ui?

I think view projection matrix makes sense per UI. But there needs to be a per-Window transformation maybe. I don't know if different projections for different windows makes sense... In the 2D use case, maybe, because they have different render targets (right?), but for 3D less so 🤔

did you measure perf difference compared to using mat3?

No... should I write a benchmark? Maybe a good thing to have that in general...

[mosra]

I think view projection matrix makes sense per UI. But there needs to be a per-Window transformation maybe. I don't know if different projections for different windows makes sense... In the 2D use case, maybe, because they have different render targets (right?), but for 3D less so thinking

No, I mean: with this you could allow separating planes from each other to position them in arbitrary locations in the 3D environment, as you said above:

having a single UserInterface with multiple panels with their own 3D transformations each.

should I write a benchmark?

Since there's only a possibility to have just the mat3 or the mat4 implementation but not both, I'm not sure if that would work. I meant rather checking this to be sure it doesn't add a significant perf drop for 2D UIs (and think about this a bit more if it actually does). You could use that VR performance HUD or some other simple mean to verify the difference, no need to have exact numbers.