public final class GlassLensBlend

Reference implementation of Graphics.glassLensRegion: the optics of a raised Liquid Glass lens (the lifted iOS 27 tab selection) laid over what is already painted. Ports without a native path run this; the Metal shader cn1_fs_glass_lens mirrors it.

The lens is a rounded rectangle (a capsule for a negative corner radius) whose rim is a circular bevel of height bevel: a pixel s inside the rim shows the surface displaced OUTWARDS along the rim’s normal by D(s) = (h - s) / sqrt(1 - ((h - s) / h)^2) (h = bevel, zero beyond it) – the refraction of a glass edge, which pulls whatever lies just outside the lens (the edge of the bar it floats over, the backdrop) into its rim. The three channels are displaced by D * (1 - dispersion), D and D * (1 + dispersion), which fringes the rim. On top of that the surface:

• brightens by brightness inside;
• darkens by up to endShade in a band endShadeWidth wide along the rim, weighted by how horizontal the rim’s normal is (the rounded ends);
• is multiplied by 1 - outline on a ring outlineWidth wide just inside the rim;
• gains a highlight of rimLight + rimLightVertical * |ny| right inside that ring, decaying as exp(-d / rimWidth) with the depth d past it;
• casts a soft shadow of depth shadow around its lower half, a band that peaks shadowWidth outside the rim and has the same width.

Lengths are in pixels, brightness levels in 0..1 units. Everything is mixed with the untouched surface by amount.