---
root:
  items:
        - type: rect
          bounds: [0, 0, 100, 100]

          # First blend black rect with green in place
          #  Cs = (1 - αb) x Cs + αb x B(Cb, Cs)
          #  B(Cb, Cs) = | Cb - Cs | = (0, 0, 0)
          #  0.5 * (0, 255, 0) + 0.5 * (0, 0, 0) = (0, 127.5, 0)
          #
          #  Now, composite the resulting color with src-over; the alpha is the original alpha for the top layer
          #  while the color is the blending result
          #  co = αs x Fa x Cs + αb x Fb x Cb  - this is premultiplied 
          #  αo = αs + αb x (1 – αs) 
          #  Source over:     Fa = 1; Fb = 1 – αs 
          # co = 0.5 * 1 * (0, 127.5, 0) + 0.5 * 0.5 * (0, 255, 0) = (0, 63.5, 0) + 0.25 * (0, 255, 0) = (0, 127.5, 0)
          # ao = 0.5 + 0.5 * 0.5 = 0.75
          #  Co = co/ao = (0, 127.5, 0) / 0.75
          #
          #  Now alpha composite on white background
          # co = 0.75 * 1 * (0, 127.5, 0) / 0.75 + 1 * 0.25 * (255, 255, 255) = (0, 127.5, 0) + (63.75, 63.75, 63.75) = (63.75, 159, 63.75) = (64, 191, 64) 
          color: [64, 191, 64]
