Lite glass

The material without the shader: frost, tint and rim, and nothing to compile.

A lens gets its look from a fragment shader: every pixel measures its distance to the shape, reads the background under it, bends it and lights itself. Lite glass gives up the bending — the half that needs a shader — and keeps everything else: the frost, the tint, and a rim lit by the same model the shader runs, evaluated on the Dart side and drawn as one triangle mesh from plain canvas geometry. No FragmentProgram, nothing to warm up, no capture on Skia, no slot in the lens budget on Impeller.

Three ways in#

It is one material with three doors. Flip the whole app, flip one lens, or use the widget directly on a surface that was never a lens.

// 1. Every lens in the app — set once, before the first lens builds.
LiquidGlassEngine.liteGlassOnSkia = true;      // Skia and the web
LiquidGlassEngine.liteGlassOnImpeller = true;  // Impeller

// 2. This lens only, on either engine — the value is its rim's pickup.
LiquidGlassLens(
  style: const LiquidGlassStyle(liteGlass: LiquidGlassLitePickup.backdrop),
  child: child,
)

// 3. The widget itself, for a card, a row, a sheet.
LiquidGlassLite(
  shape: const LiquidGlassShape(cornerRadius: 22, borderWidth: 1.5),
  blur: const LiquidGlassBlur(sigmaX: 3, sigmaY: 3),
  color: const Color(0x33FFFFFF),
  child: child,
)

With an engine switch on, a LiquidGlassView takes no glass capture at all — the adaptive sampler is not a capture and keeps running — and every lens beneath it draws lite glass, the same thing a lens outside any view already draws. That is the way to put the material on a page that has too many lenses for the shader, or on a device that has no time for it, without touching a single lens.

What a lens keeps#

A lens drawn lite keeps its shape, its appearance's color, blur and shadow, and its refraction's magnification as a flat zoom in the frost's own filter. The distortion band, the chromatic aberration and the edge bend are gone — there is no refraction in any mode. The rim stays, at the same numbers: borderWidth, lightColor, lightDirection, lightIntensity, and the OpticalBorder or ClassicBorder parameters mean what they mean on a real lens. The silhouette is the outline a lens clips to, so all three corner styles are reproduced exactly.

What still works, and what does not#

Lite glass changes how a lens is drawn, not what the tree around it does. Everything that never needed the shader keeps working; the two things that are the shader do not.

Where the rim gets its colour#

The shader's rim samples the background under each pixel and tints its highlight with it, so over a photograph the rim is red where it crosses red and blue where it crosses blue. LiquidGlassLite.pickup — and liteGlass on a lens's style, which is the same value — is the lite answer to that, and it is a choice of cost:

ambientColor is the fourth way, and it is orthogonal: hand the widget one colour — a sampled backdrop, or whatever the surface sits on — and it goes through the shader's own highlight math, tinting the whole rim at once. Free, but one tone for the whole outline, and only the painted modes take it.

What it costs#

• The frost is one backdrop read. Blur and magnification go through one filter, so adding magnification to a blur adds no read.
• A `backdrop` rim is a second read. Blur at zero, magnification at one and that rim is one read, for the rim.
• `none`, `blend` and `surface` read nothing. With blur at zero and magnification at one, the whole widget is a few drawVertices calls — put a fill of your own behind it and it is nearly free. That is the shape to reach for in a long list.