public final class GlassRecipe

The iOS 27 chrome-bar material.

LIGHT IS DELIBERATELY IDENTICAL to liquidChrome(boolean). Fitting the transform against the iOS 27 capture returned sat 1.09, scale 0.860, offset 18.9 where iOS 26 is 1.10 / 0.850 / 20.0 – inside 1.3% on every parameter, at an rms of 1.27/255. That is a measurement saying “unchanged”, so the iOS 26 numbers are reused verbatim rather than replaced by a near-identical duplicate that would read as a real difference.

DARK is the best affine fit (rms 14.6/255) and is KNOWN NOT TO BE EXACT. See liquidPanel27(boolean) for why dark cannot be fitted properly.

The iOS 27 floating-pill material.

LIGHT is again measured as unchanged – the fit returned 1.86 / 0.984 / 111.4 against iOS 26’s 1.80 / 1.000 / 108.0 – so the iOS 26 values are reused. DARK is the best affine fit and, like chrome, is approximate.

The iOS 27 glass-panel material, and the recipe that carries the method these three were measured with.

HOW THE NUMBERS WERE OBTAINED. The material is the documented affine transform c' = clamp((lum + (c - lum) * sat) * scale + offset). The iOS 26 constants are known, so every interior pixel of a committed goldens/ios-26-metal tile can be inverted back to the backdrop that produced it, and the matching goldens/ios-27-metal pixel then fitted against that same backdrop. Nothing about the backdrop has to be assumed, and because the transform is linear it commutes with the Gaussian blur, so the blur does not bias the fit. Clipping does NOT commute, so a pixel is used only when nothing within the blur’s reach clipped – without that erosion the photo-backdrop tile fitted at rms 14 against rms 1 for the flat ones, and it dragged every parameter with it.

The method self-checks: run against the iOS 26 set it recovers the iOS 26 chrome constants it was never told, to within 1.3%.

WHY DARK IS APPROXIMATE, IN ALL THREE RECIPES. After the best affine fit, the light residual is flat across the whole backdrop-luma range (within +/-0.9/255). The dark residual is not: on the chrome bar it runs +8.9 at low luma, -9.3 through the middle and +10.3 at high luma – a systematic curve, not noise. iOS 27’s dark glass therefore applies a NON-LINEAR luminance response, and no choice of sat/scale/offset can express it, because this transform is affine by construction. Matching dark properly needs a curve term in the material model and in every port’s shader, which is a larger change than new constants; these values are the closest an affine material gets until then.