Release 2.14 of Tilengine adds a new layer window feature, based on the actual SNES hardware.

This feature extends original layer clipping that was already implemented in Tilengine. However, layer windowing is much more powerful:

• can be set to normal o inverse: instead of clipping the outside, it clips the inside
• color math with clipped region: the cut-out region can be set to one of three modes:
  • transparent: by default, the underlying layer can be seen where the upper layer is cut (same as classic layer clip)
  • solid color: the masked region can be filled with a constant color
  • color math: the masked region is set to one of available color blending modes, combining a solid color and the underlying layer

New example LayerWindow (https://github.com/megamarc/Tilengine/blob/master/samples/LayerWindow.c) allows to play with combinations of features:

• Outside clipping, shows the underlying layer. Equivalent to classic "layer clipping"

• Inverse clipping  (clips the inside) with blue color applied with blending function to the inner hole

Using raster effects to modify the window edges on each scaline allows free-form clipping, the same trick used in Super Mario World where a circle and keyhole shapes scaled up and down to create a transition between layers.

These screenshots from new sample LayerCircle (https://github.com/megamarc/Tilengine/blob/master/samples/LayerCircle.c) allow moving a circle and change its radius to mask the main layer, filling the outside part with blue: