OSGText Issues
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we need to do some Real Work (TM) to support Canvas with osgText 3.6 and upwards, unfortunately.[1]
OSGText doesn't play nice with shaders.[2]
some developers have switched to canvas /because/ of the always white OSGText problem[3]
The OSGText issue is more that the world is moving forwards, and our text-animation element has not. (Shaders required, can’t rely on OpenGL 1.1 built-in lighting)[4]
It’s caused by OSG using a shader to render text now, but this bypasses the built-in emissive/diffuse/ambient material properties, which is what our <text> animation uses to set colours of text.
It should happen ‘everywhere’ that a shader is used to render text - Canvas doesn’t care about it since it sets the text color directly.[5]
The breaking change was introduced with OSG 3.6.5, and was also recently merged into OSG 3.7.[6]
Background
For the time being, we don’t (often) use OSG 3.6 - looking at the code on master (which became 3.6), there isn’t a single commit we can revert - Robert evidently did a lot of incremental improvements to the text code, adding support for other features and improving the shader support. Then at some point he collected a subset of those changes and back-ported them to 3.4 branch, which is what we revert in the commit on my fork on GitHub.
This means for OSG 3.6 we need to find a solution on our side, which likely means updating aircraft or making some guesses based on the <text> animation element in our XML files, because the set of colouring options supported by the new osgText implementation is more restrictive than what worked before.
(The text animation assumes that setting all of emissive/ambient/diffuse/specular works on an osgText, and it no longer does - for some cases we could map the emissive color to the text color, but this would break some other cases…. and text still won’t receive normal lighting in that case)[7]
Investigation
Fernando has been investigating this for a while now and it has proven to be a lot less trivial that he initially thought. His first approach was to ust transform the osgTexts into EffectGeodes, but this isn't so elegant as the general rules of effects don't apply to animations (we can't use <inherits-from>, model-default doesn't get applied automatically as it isn't considered a model, etc).
Richard said on Discord that another option was creating a Canvas for each text animation, but creating a FBO for every small piece of text doesn't sound very performance-friendly. This is also worsened by the fact that canvas cameras are scene-graph level cameras and are being rendered multiple times (once per viewer slave camera).[8]