Module blend 

Blend mode pipeline variants and runtime blend-state selection.

OxiUI’s oxiui_core::paint::DrawCommand::SetBlendMode allows UI elements to be composited with custom blend operations (Multiply, Screen, Overlay, etc.). This module provides:

• blend_state_for_mode — map a BlendMode to a wgpu::BlendState.
• BlendPipelineSet — a set of pre-compiled solid-pass pipelines, one per supported blend mode. Switching blend modes within a frame is achieved by calling set_pipeline with the appropriate variant rather than recreating a pipeline at runtime.

wgpu blend-state mapping

BlendMode	wgpu colour blend equation
Normal	Src + Dst × (1 − SrcAlpha) (standard source-over)
Multiply	Src × Dst + Dst × 0
Screen	Src + Dst − Src × Dst (approx: Src + Dst × (1-Src))
Overlay	Not directly expressible in fixed-function blend;
	falls back to Normal in hardware blend mode.
Darken	min(Src, Dst) — not expressible; falls back.
Lighten	max(Src, Dst) — not expressible; falls back.
Copy	Src × 1 + Dst × 0 (replace).
Destination	Src × 0 + Dst × 1 (no change).

Modes that require per-pixel arithmetic beyond what fixed-function hardware supports (Overlay, Darken, Lighten) fall back to Normal. A future improvement could implement them via custom fragment shader variants.

Structs

BlendPipelineSet

A set of pre-compiled solid-pass pipeline variants, one per blend mode.

Functions

blend_state_for_mode

Return the wgpu::BlendState that best approximates mode.