Add gamma correction to simple_demo_qml example

[athenaz2]

🦟 Bug fix

Summary

When running with Ogre2 and OpenGL, simple_demo_qml has darker shadows and the scene is a bit darker overall when compared to simple_demo. This is because the texture from the render engine is in sRGB color space, but Qt's textures are created in linear color space. As per gazebosim/gz-gui#629, this fix for simple_demo_qml ensures that the render engine texture, originally in sRGB format, is correctly passed to Qt in linear format. Thus, now the simple_demo_qml scene is lighter and matches simple_demo's scene.

Edit: modified changes as per gazebosim/gz-gui#630. Original changes copied render texture to a new internal texture before passing to Qt. Now, add a parameter to the render texture that disables sRGB decoding (only one time, not every frame) such that there is no sRGB -> linear conversion when texture is copied from Ogre2 to Qt, and now Qt displays it as-is as sRGB.

Before

After

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.63%. Comparing base (5859051) to head (72abe1c).
Report is 17 commits behind head on gz-rendering8.

Additional details and impacted files

@@                Coverage Diff                @@
##           gz-rendering8    #1019      +/-   ##
=================================================
- Coverage          75.68%   75.63%   -0.06%     
=================================================
  Files                177      177              
  Lines              16959    16993      +34     
=================================================
+ Hits               12835    12852      +17     
- Misses              4124     4141      +17     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[iche033]

can you make these ids member variables so that we can delete the fbo and texture in the destructor when the app exits? e.g. see code here

[iche033]

this will create a new fbo every frame. So related to previous comment, we need to store this id and as member var, and here only create the frame buffer if the fbo does not exist yet, i.e. rhiFbo is 0. Same goes for the glGenTextures line below