ImGuiIntegration: make ImFontAtlas texture accessible

[rune-scape]

Fixes #60

[codecov-io]

Codecov Report

Merging #61 into master will decrease coverage by 0.57%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #61      +/-   ##
==========================================
- Coverage   74.55%   73.97%   -0.58%     
==========================================
  Files          21       21              
  Lines         900      903       +3     
==========================================
- Hits          671      668       -3     
- Misses        229      235       +6

Impacted Files	Coverage Δ
src/Magnum/ImGuiIntegration/Context.h	100% <ø> (ø)	⬆️
src/Magnum/ImGuiIntegration/Context.cpp	82.28% <66.66%> (-0.86%)	⬇️
src/Magnum/DartIntegration/ConvertShapeNode.cpp	93.92% <0%> (-2.21%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 43e86c2...d66065c. Read the comment docs.

[mosra]

Thank you (and extra thanks for writing the docs as well 👍).

One more thing -- could you do simplify the ternary condition we talked about? You mentioned it worked well in your last comment in #60. (To be extra sure, if you could test that also an ImGuiIntegration::image() widget still work as expected after that change, that'd be great.)

[mosra]

Could this be just atlasTexture()? Magnum doesn't use get prefixes anywhere else.

[rune-scape]

yes, my bad

[mosra]

Merged as b3c65b9, thank you! :)

[rune-scape]

btw i have been testing with the ternary statement simplified, and everything works

[Squareys]

There is a tiny bug in here:

When the Context is moved, the pointer to _texture is invalidated so that the ImGui font TexID points to invalid memory. The TexID needs to be updated in Context(Context&&).

I will follow up with a tiny PR.