Module shadow 

Shadow rendering: mask → 2-pass Gaussian blur → composite onto main target.

For each ShadowDesc:

1. Clear ping texture to transparent.
2. Render white rect mask of the (offset-shifted) rect into ping using the solid pipeline.
3. Horizontal blur ping → pong.
4. Vertical blur pong → ping.
5. Composite ping (tinted by shadow colour) onto the main target_view using LoadOp::Load (alpha blending — shadow renders under content because it is composited before the solid/gradient/textured passes).

When blur_radius <= 0.5 the blur passes are skipped and the white mask is composited directly, yielding a crisp (hard-edge) shadow.

Ping-pong textures are allocated once per render_shadows call and shared across all shadows in the draw list.

Structs

ShadowDesc

A parsed, ready-to-render shadow.

ShadowGpuState

GPU device/queue state needed for shadow rendering.

ShadowPipelines

The three GPU pipelines needed for shadow rendering.

ShadowRenderStats

Render pass and draw call counts accumulated across all shadow descriptions submitted by a single render_shadows call.

Constants

MAX_BLUR_RADIUS

Maximum Gaussian blur radius in pixels. Clamped to bound the tap-loop iteration count (2 * MAX_BLUR_RADIUS + 1 = 129 iterations worst-case).

Functions

collect_shadows

Collect all DrawCommand::BoxShadow entries from list into ShadowDesc values, translating each rect by its offset.

render_shadows

Render all descs shadows, compositing each onto gpu.target_view.