Final shader applied on overlay

[samoncrief]

@Meakk Here's the current version with linear blending applied. The code is all handled in vtkF3DOverlayRenderPass.

Fix for #1500

[mwestphal]

Sorry I canceled your run, working on a CI issue right now

[mwestphal]

I restarted CI :)

[mwestphal]

LGTM but its more a @Meakk style of code.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.75%. Comparing base (695141f) to head (54867a8).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1984      +/-   ##
==========================================
+ Coverage   95.69%   95.75%   +0.06%     
==========================================
  Files         126      128       +2     
  Lines       10219    10293      +74     
==========================================
+ Hits         9779     9856      +77     
+ Misses        440      437       -3     

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[mwestphal]

LGTM appart the small codepath that is not reached by coverage

[mwestphal]

LGTM but this will need @Meakk review as well

[Meakk]

Amazing work @samoncrief!
Can you add a new test with a final shader (e.g. negative shader) and a filename to properly test that the filename widget isn't affected?

[samoncrief]

Amazing work @samoncrief! Can you add a new test with a final shader (e.g. negative shader) and a filename to properly test that the filename widget isn't affected?

Sure. Do you want it for a shader where alpha equals 1.0 like in the examples, or with the alpha values preserved? The example code treats the background as a solid object because of the alpha, so it may not give the intended results.

[Meakk]

Do you want it for a shader where alpha equals 1.0 like in the examples, or with the alpha values preserved?

It's up to you :)