Extracts the polyline outline(s) of an AlphaMask's solid
region(s) in mask-local coordinates.
Useful for visualizing what a sprite's pixel-perfect collision
footprint actually looks like — a UI overlay that traces the
outline of solid pixels rather than the rectangular AABB. Demo 08
uses this to draw the sprite's "real" border.
Implementation: builds a single-chunk temp bitmap whose interior
matches the mask (with 1 px of air padding so the contour closes
locally), runs marching squares on it, and applies Douglas-Peucker
with epsilon. Output coordinates are in mask-local space ((0, 0)
is the mask's top-left corner). Translate by the mask's scene
position to draw.
Extracts the polyline outline(s) of an AlphaMask's solid region(s) in mask-local coordinates.
Useful for visualizing what a sprite's pixel-perfect collision footprint actually looks like — a UI overlay that traces the outline of solid pixels rather than the rectangular AABB. Demo 08 uses this to draw the sprite's "real" border.
Implementation: builds a single-chunk temp bitmap whose interior matches the mask (with 1 px of air padding so the contour closes locally), runs marching squares on it, and applies Douglas-Peucker with
epsilon. Output coordinates are in mask-local space ((0, 0)is the mask's top-left corner). Translate by the mask's scene position to draw.