Wet & material strokes

Inflated geometry: Geometry is built wider than the visible mark, and the shader receives the position of the visual edge inside that margin, so effects that reach past the stroke have fragments to land on.

Background sampling: The background is sampled by screen position, not by the stroke's own coordinates.

Caps: Ends are carved in the shader inside the same margin, so one quad past the end serves rounded, square, and ragged caps.

Watercolor: The wash reads a pre-blurred copy of the background, one texel per fragment, instead of gathering a neighborhood. Pigment collects just inside the boundary, leaving a darker rim.

Smear: Each fragment samples backward along the stroke's direction in screen space and averages the result, so the background streaks the way the mark traveled. The sampling distance varies with noise across and along the mark.

Wet brush: The drag runs first, over a mix of the sharp and blurred background, and the wash then tints the result.

Drag: Each fragment samples backward along the stroke's direction, the same walk as the smear, with the reach varied by lane noise.

Paint: The dragged background is mixed under the stroke's color at a high ratio, thinner where the height field dips, so the background survives only as streaks in the crevices.

Lighting: Ridges stretched along the path supply a surface normal, and diffuse and specular lighting from a fixed light make the relief read as thickness. The drag and the ridges share one lane noise, so the paint that moved furthest also sits highest.

Height field: Height is built from distance to the edge, which rounds the cross-section into a bead, plus noise stretched along the path, which reads as liquid dragged along the stroke. The surface normal comes from finite differences in the stroke's own frame.

The bead is parabolic, not a hemisphere: a hemisphere's slope is infinite at the rim, which breaks the finite differences there. Height and the across coordinate are both measured in half-widths, so the gradient is dimensionless at any width.

Chrome: The environment is two tones split at a horizon; the boundary sweeping across the curved surface reads as metal.

Mirror: The reflected direction is used as a screen-space offset into the background, so the reflection costs one texture read but cannot show anything outside the frame. Contrast is pushed after sampling.

Glass: Refraction offsets the background lookup along the surface normal, largest where the surface tilts most. Reflection is mixed in by a Fresnel term (mirror-like at glancing angles).