kitepdf-native-renderer/io.github.yuroyami.kitepdf.nativerenderer/AwtCanvas/applySoftMask

applySoftMask

open override fun applySoftMask(kind: SoftMask.Kind, maskBBox: KiteRectangle, maskCtm: KiteMatrix, render: () -> Unit, renderMask: (KiteCanvas) -> Unit)

open override fun applySoftMask(kind: SoftMask.Kind, maskBBox: KiteRectangle, maskCtm: KiteMatrix, transfer: KiteMaskTransfer?, render: () -> Unit, renderMask: (KiteCanvas) -> Unit)

Soft mask (ISO 32000-1, 11.6.5): the content paints into its own transparent layer, the mask scales that layer's alpha, and the layer then composites onto the page once. The backdrop is never read or masked (#78), the layer has alpha whatever the destination type (#80), and the mask group's colours never reach the page (#79). Skia and Compose use the same layer model.

One native blit replaces a per-pixel readback of the page, which made masked pages 3 to 44 times slower (#256). When every paint in the content used one blend mode, the layer composites with that mode, so a masked Multiply shadow still multiplies. Content that mixes blend modes renders again on the exact, slower backdrop path. The transfer table maps each mask value once, on both paths.