Draw calls will be increased a lot when using a custom font in Label (broken batching)

[AllenDang]

Tested versions

• Reproducible in 4.4 stable

System information

macOS v15/windows 11

Issue description

A label control with lots of texts behave differently with custom font. With default font, draw call is 31, with custom font, draw call increased to 237.

Steps to reproduce

1. Create a new project.
2. Create a new 2d scene.
3. Add a label and set lots of Chinese text.
4. Run, in editor -> debugger -> monitor, and pick draw call, notice the total draw call is 31.
5. Stop
6. Set label's theme_override -> fonts to load a custom font
7. Run, notice the total draw call increased to 237

Minimal reproduction project (MRP)

2d_batching_test.zip

[zaevi]

This may depend on the characteristics of diferrent fonts (such as shaping).

• fusion-pixel-12px-monospaced-zh_hans (dc always be 1):

---

• DroidSansFallback (dc seems to change with control size):

dc.webm

[AllenDang]

@zaevi Thing is fusion-pixel-12px-monospaced-zh_hans does have 1 dc in macOS v15, but have 151 dc in windows 11.

Here is the screenshot from windows 11.

[zaevi]

I also tested it on Windows 11

System information

Godot v4.5.dev.mono (0013d30) - Windows 11 (build 22631) - Multi-window, 2 monitors - OpenGL 3 (Compatibility) - NVIDIA GeForce RTX 4090 (NVIDIA; 32.0.15.6094) - 13th Gen Intel(R) Core(TM) i7-13700F (24 threads)

(Same result on 4.4.stable)

[chocola-mint]

Looking into this with RenderDoc, the renderer seems to be alternating between two different 256x256 white textures that look completely identical.

Here's the capture for those interested: capture-godot-104537.zip

Out of curiosity I also tested out the project with the Forward+ renderer (Vulkan backend) and while the draw call issue is present, there's a bit more information here.

It seems that the character glyphs are split into multiple 256x256 atlases. Having to switch between atlases when rendering is what's causing the batches to break. And presumably this atlas generation is different depending on the how the glyphs are loaded dynamically, which is why the result can differ between machines and fonts.

A larger atlas size would be enough to address this issue, though this doesn't seem to be configurable on the user's end.

And again, here's the Vulkan capture for those interested: capture-godot-vulkan-104537.zip