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# Position Operations

A position is a pixel location within a viewport. The upper-left corner is pixel (0, 0) and the orientation of the position coordinates within a viewport is as follows:

- `(make-posn x y)`
  Takes two integers and returns a position with the specified x and y coordinates.
- `(posn-x p)`, `(posn-y p)`
  Return the x and y coordinates, respectively, of a position.
- `(posn? v)`
  Reports whether v is a position.
- `((get-pixel viewport) p)`
  Returns the color of the pixel at position p in viewport; 0 denotes white and 1 denotes not white.
- `((get-color-pixel viewport) p)`
  Returns an RGB value for color of the pixel at position p in viewport.
- `((test-pixel viewport) color)`
  Returns the color that will actually be used if color is used to draw.