Module shadow 

Box shadow via separable 1-D Gaussian blur with a kernel cache. Box-shadow via separable 1-D Gaussian blur with a cached kernel.

A drop shadow is rendered by:

1. Painting the shadow rectangle at (rect + offset) in the shadow colour.
2. Extracting the alpha channel of that rectangle.
3. Applying a separable horizontal + vertical Gaussian blur to the alpha.
4. Compositing the blurred shadow alpha under the framebuffer content.

All operations are pure Rust — no SIMD, no FFT, no external crates.

Structs

GaussianCache

A cache that stores pre-computed Gaussian kernels keyed by blur-radius bits.

Functions

box_shadow

Render a drop (or inset) box shadow for a rectangle rect into fb.

gaussian_blur_alpha

Apply a separable Gaussian blur to the alpha channel of a rectangular region within alpha (a flat width × height f32 buffer).

gaussian_kernel

Compute a normalised 1-D Gaussian kernel with sigma = blur_radius / 2.