Make it possible to change character transform in RichTextEffect

[botero-dev]

This PR adds a Transform2D field to the CharFXTransform object, this lets a subclass of RichTextEffect to specify custom transforms including rotations and scaling. Partially implements godotengine/godot-proposals#3417

charfxtransform.demo.mp4

Additionally, I moved an include so rebuilds are faster.

[djrain]

Just found myself wanting this, and came looking - nice timing! Can it be set up to scale from the center of the glyph by default? I imagine that would be desired in most cases.

[botero-dev]

I did some cleanup and ran some experiments.
The transform origin is still the baseline left. It makes the most sense to keep it there because then it is easy to apply offsets before and after the transform to shift the transform origin.

The two problems I found:

• Font size is not sent to the user in the CharFXTransform data structure. Font size is needed to get some glyph metrics.
• Shadows are transformed using the glyph origin instead of the shadow origin. for outlines it makes sense but for shadows it feels weird.

Also, the text server, and some font-wide metrics like ascent and descent could be provided by CharFXTransform, as it is very likely that these will be asked for from scripting anyways.

Those will get tackled in my next pass. For now enjoy one of my tests:

charfxtransform.demo2.mp4

[botero-dev]

Had some more fun today:

To achieve this, I ended up setting the transform from whatever location the layout engine tells me it would place the character, and letting the user transform this (instead of my previous attempt of using an identity transform and adding the offsets myself right before the drawing.

Effects can be stacked: (the lag at the beggining seems to be screen recording program)

44a4d9e5f939ef269f18b3bf1666f42e.mp4

You can try out these by compiling and running this demo project:
TextTransformEffects.zip
The curves need to be reassigned when launching the project, I guess it is some Godot serialization issue out of the scope of this issue.
Additionally I found an issue with Curve2D sampling but I'll report that one separately in a minute.

I am in a point where the feature would be good enough for my usage, but I feel like some feedback on this would be appreciated. some points to discuss:

• I would like shadows to be transformed using their own pivot instead of the main character pivot, so when I rotate a glyph 180 degrees, the shadow would still be shifted down. This could be done in two ways:

  • pushing the shadow transform separately with its own draw_set_transform_matrix call
  • somehow relying on the user applying this offset himself (and forwarding the shadow offset data to the user through the CharFXTransform)

• When calling font_draw_glyph_outline It asks for offset coordinates, I assume that internally it would try to do sub-pixel antialiasing if the inputs are right... I am changing those values and actually making those values after the user may have done many transform operations. Is there anything I should do to play well with the system?

I still haven't exposed font_size to the CharFXTransform object, so that will be part of my next push.

[KoBeWi]

Forward declarations should be created at the top of the file. (although it's interesting that you can inline them 🤔)

[KoBeWi]

This shouldn't be in the code. You could write a comment in the PR instead.

[KoBeWi]

I tested that it works, but I can't say if the implementation is 100% correct (looks fine to me tho). I mainly wonder if there is some negative performance impact if someone doesn't modify the transform, because the char is transformed regardless of that.

[IntangibleMatter]

I've been thinking about something like this lately too! It would make text effects wayyyyy more versatile, and it would make godotengine/godot-proposals#7270 even more powerful!

[akien-mga]

@0xafbf Are you able to address the review comments?

The PR should also be rebased, and the commits squashed into one.

[botero-dev]

yes, I'll update this pr by the end of the week

[botero-dev]

Hello, I updated the PR with some improvements:

• Cleaned up most of the suggestions
• Added the paragraph offset to the character offset so effects can deal better with multi line texts
• Added some code that fixes shadows (so 180º rotated glyphs don't draw the shadow in the opposite direction)

I feel the same concern on pushing transform matrices per character. I don't know how to profile that very well, but I guess that adding a hundred of RichTextLabel should do the trick. I'll do that in my next pass

For optimization, I have conflicting ideas on what approach to take:

• Have a boolean that only marks true if an ItemFX effect is found, that way we can avoid other checks elsewhere
• Have a boolean set in the RichTextEffect script similar to how the BBCode name works, that we can read internally to enable transform matrices
• Check the matrix that is about to be pushed vs the last pushed, and avoid doing it if it is the same, the downside of this is that matrix math needs to be done either way

In the end it may not be the worst thing to push one matrix per character, because in the end we can filter it so only happens when ItemFX are used (so for example documentation viewer wouldn't push matrices per character), and the rest of the strings that would use this would very likely not exceed a hundred of characters. I think we'll know better when I do the tests

Also, Drawing shadows uses a different transform. On one hand I think that we can do some inverse transforms to find the location to layout the shadow so it is placed correctly when it is drawn. But that feels hacky and maybe not very valuable for the reason mentioned above. On the other hand I think that it would be cool to extend the RichTextEffect system to tell the user if the character being processed is a shadow, an outline, or the character itself, and let the user apply color and transform effects individually for each of these passes. That would be done out of the scope of this PR, and maybe require some changes on how the text render passes are issued.

I include an updated version of the example project with some implemented effects to aid in testing:

TextTransformEffects.zip

[akien-mga]

Thanks!

[feserr]

In which version it will be added? 4.2?

[akien-mga]

Yes, refer to the milestone in the side bar: