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posn
get-pixel
get-color-pixel
test-pixel

2 Position Operations

A position is a pixel location within a viewport. The upper-left corner is pixel (0, 0), and positions increase to the right and down.

(struct posn (x y)
  #:extra-constructor-name make-posn)
  x : real?
  y : real?
Represents a positions.

((get-pixel viewport) p)  (one-of/c 0 1)
  viewport : viewport?
  p : posn?
Returns the color of the pixel at position p in viewport; 0 denotes white and 1 denotes not white.

((get-color-pixel viewport) p)  rgb?
  viewport : viewport?
  p : posn?
Returns an rgb value for color of the pixel at position p in viewport.

((test-pixel viewport) color)  rgb?
  viewport : viewport?
  color : 
(or/c (integer-in 0 299)
      string?
      rgb?)
Returns the color that will actually be used if color is used to draw.