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