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
(struct posn (x y)
#:extra-constructor-name make-posn)
x : real?
y : real?

Represents a positions.

procedure
((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.

procedure
((get-color-pixel viewport) p) → rgb?
viewport : viewport?
p : posn?

Returns an rgb value for color of the pixel at position p in viewport.

procedure
((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.

1	Basic Commands
2	Position Operations
3	Color Operations
4	Draw, Clear, and Flip Operations
5	World Operations
6	Miscellaneous Operations
7	An Example
8	A More Complicated Example
9	Protecting Graphics Operations
10	Mouse Operations
11	Keyboard Operations
12	Flushing
13	Graphics Library as a Unit