Feature Request: Path-Aligned Gradient

[qianxiaoming]

Problem

Current gradient rendering is defined in screen/user space and is not aware of path geometry. As a result, it cannot produce a continuous color transition that follows a polyline or curved path.

Desired Behavior

We want to support gradients that are bound to the path itself, such that:

• Color transitions follow the direction and length of a stroke or path
• The gradient is continuous across multi-segment polylines and curves
• No visible discontinuities appear at segment joins or sharp turns
• The gradient remains consistent under transforms (scale, rotate, etc.)

Goal

Enable a single gradient definition to smoothly map along the entire path as if the color is driven by the path’s intrinsic parameterization (e.g. arc-length), rather than by screen-space coordinates.

[thomasp85]

FYI I have been working on this as well, decomposing the path into a mesh and rendering the mesh. This works well but does add anti-aliasing seems between the triangles since Vello doesn't have a mesh renderer yet (see #1709)

An example render:

[qianxiaoming]

@thomasp85 This is indeed the effect I wanted! Perhaps this rendering capability can be used in the near future?

[thomasp85]

I'm happy to share the code, but it as said, the output is not pixel-perfect due to the seams so I'd rather wait until a proper mesh renderer exist