<p> SCHEME DRAWING COMMANDS Commands are case-sensitive, use lower-case ;; Documentation, not a command, comments for human user start Opens a drawing canvas, 2 arguments – width and height make-posn Plots a point, a position, 2 arguments – X and Y coordinates draw-circle 3 arguments – center position, radius, color draw-solid-disk 3 arguments – center position, radius, color draw-solid-rect 4 parameters – top left corner, width, height, color draw-solid-line 4 parameters – left end point, right end point, color (color optiona l - defaults to black)</p><p>DEFINITIONS Uses open and close parenthesis define Defines a constant and a function</p><p>COLOR CONSTANTS Case-sensitive – use lower-case characters ‘white Can erase part of a shape if on top and background is white ‘black Used to outline objects ‘red R ‘blue B ‘green G RBG are basic colors in digital graphics ‘yellow More colors available in advanced graphics library</p><p>ARITHMETIC OPERATORS (operator operand..operand) (action data) + (+ 3 4) (+ ½ ¼) - (- 3 4) (- (+ 5 6) (- 8 9) ) / (/ 3 4) (+ (/ 5 6) -8) * (* 3 4) (- (* 9 8) (* 3 4) ) Can use the interaction window for parameter value planning</p><p>LOGICAL OPERATOR (Returns a Boolean value – true or false) and Used to combine shapes - drawing commands always returns true </p><p>Pre-defined FUNCTION CALLS Set library: Language / TeachPack / HTDP / draw.ss (start 640 480) ;; (start canvasWidth canvasHeight) (make-posn 320 240) ;; (make-posn x-coordinate y-coordinate) (draw-circle (make-posn 150 200) 38 ‘red) ;; (draw-circle centerPoint radius color) (draw-solid-disk (make-posn 320 150) 50) ;; (draw-solid disk centerPoint radius color) (draw-soilid-rect (make-posn 0 450) 640 30 ‘green) ;; (draw-solid-rect topLeftPostion width height color) (draw-solid-line (make-posn 150 240) (make-posn 150 350)) ;; (draw-solid-line startPoint endPoint color) ;; Note the color is optional, default to black</p><p>CONSTANT DEFINITIONS (define MID-X 320) ;;(define NAME value) (define MID-Y 240) ;;Midpoints of a 640 x 480 canvas</p><p>PROGRAM DEFINITIONS ;;contract showing input and output (define (centerCircle radius color) ;;centerCircle: number color -> Boolean (draw-circle (make-posn MID-X MID-Y) radius color)) ;;returns true and draws a circle centered on a 640x480 canvas of variable size and color</p><p>CALLS ;;call function by its name then the actual data (centerCircle 30 ‘red) ;; variable parameters are matched with input values (centerCircle 25 ‘blue) (functionName dataForRadius dataForColor)</p><p>| How to Design Programs, TeachScheme! Project, Software www.htdp.org See book for tutorial and more commands | | Graphic Programming Module Lessons www.knorth.info under Graphics link | </p>