RgbaGradient

A color ramp of 8-bit sRGB stops with alpha — rendering-revamp §RVG-2.

Declared in src/libs/libstyle/RgbaGradient.hpp.

Detailed description

The value type of the gradients a material evaluates, and of the RGBA editor in libwidgets. libpaint's spectral gradient is a different type, because its stops are spectra and its blend is spectral (gradients §GR-4.2); the two share the editor, not the value.

The sampling rule is the one the material GLSL follows (§RVG-4), so the editor and a surface show the same color:

1. Convert each stop from sRGB to linear light.
2. Interpolate linearly between the two stops around t, alpha too.
3. Below the first stop and above the last, hold the end color.

Invariants, which isValid() checks: at least two stops, the first at 0, the last at 1, positions strictly increasing.