nand2tetris/projects/12/Screen.jack

// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/12/Screen.jack

/**
 * A library of functions for displaying graphics on the screen.
 * The Hack physical screen consists of 512 rows (indexed 0..511, top to bottom)
 * of 256 pixels each (indexed 0..255, left to right). The top left pixel on 
 * the screen is indexed (0,0).
 */
class Screen {
    static Array twoToThe;
    static boolean color;

    /** Initializes the Screen. */
    function void init() {
        let color = true;
        let twoToThe = Array.new(16);
        let twoToThe[0] = 1;
        let twoToThe[1] = 2;
        let twoToThe[2] = 4;
        let twoToThe[3] = 8;
        let twoToThe[4] = 16;
        let twoToThe[5] = 32;
        let twoToThe[6] = 64;
        let twoToThe[7] = 128;
        let twoToThe[8] = 256;
        let twoToThe[9] = 512;
        let twoToThe[10] = 1024;
        let twoToThe[11] = 2048;
        let twoToThe[12] = 4096;
        let twoToThe[13] = 8192;
        let twoToThe[14] = 16384;
        let twoToThe[15] = 16384 + 16384;
        return;
    }

    /** Erases the entire screen. */
    function void clearScreen() {
        var int x, y;
        var boolean prevColor;
        let x = 0;
        let y = 0;
        let prevColor = color;
        let color = false;
        while (x < 256) {
            while (y < 512) {
                do Screen.drawPixel(x, y);
                let y = y + 1;
            }
            let x = x + 1;
        }
        let color = prevColor;
        return;
    }

    /** Sets the current color, to be used for all subsequent drawXXX commands.
     *  Black is represented by true, white by false. */
    function void setColor(boolean b) {
        let color = b;
        return;
    }

    /** Draws the (x,y) pixel, using the current color. */
    function void drawPixel(int x, int y) {
        var Array address, value;
        let address = (32 * y) + (x/16);
        let value = Memory.peek(16384 + address);
        if(color) {
            let value = value | twoToThe[x & 15];
        } else {
            let value = value & (~(twoToThe[x & 15]));
        }
        do Memory.poke(16384 + address, value);
        return;
    } 

    /** Draws a line from pixel (x1,y1) to pixel (x2,y2), using the current color. */
    function void drawLine(int x1, int y1, int x2, int y2) {
        var int dx, dy, a, b, diff;
        let dx = x2-x1; 
        let dy = y2-y1;
        let a = 0;
        let b = 0;
        let diff = 0;
        if(dx = 0) {
            while(~(dy = 0)) {
                do Screen.drawPixel(x1, y1 + dy);
                if(dy > 0) {
                    let dy = dy - 1;
                } else {
                    let dy = dy + 1;
                }
            }
            return;
        }
        if(dy = 0) {
            while(~(dx = 0)) {
                do Screen.drawPixel(x1 + dx, y1);
                if (dx > 0) {
                    let dx = dx - 1;
                } else {
                    let dx = dx + 1;
                }
            }
            return;
        }
        while((~(Math.abs(a) > Math.abs(dx))) & (~(Math.abs(b) > Math.abs(dy)))) {
            do Screen.drawPixel(x1 + a, y1 + b);
            if(diff < 0) {
                if(dx > 0) {
                    let a = a + 1;
                }
                if(dx < 0) {
                    let a = a - 1;
                }
                let diff = diff + Math.abs(dy);
            } else {
                if(dy > 0) {
                    let b = b + 1;
                }
                if(dy < 0) {
                    let b = b - 1;
                }
                let diff = diff - Math.abs(dx);
            }
        }
        return;
    }

    /** Draws a filled rectangle whose top left corner is (x1, y1)
     * and bottom right corner is (x2,y2), using the current color. */
    function void drawRectangle(int x1, int y1, int x2, int y2) {
        var int dy;
        let dy = y2 - y1;
        while(~(Math.abs(dy) = 0)) {
            if (dy > 0) {
                do Screen.drawLine(x1, y1 + dy, x2, y1 + dy);
                let dy = dy - 1;
            } else {
                do Screen.drawLine(x1, y1 + dy, x2, y1 + dy);
                let dy = dy + 1;
            }
        }
        return;
    }

    /** Draws a filled circle of radius r<=181 around (x,y), using the current color. */
    function void drawCircle(int x, int y, int r) {
        var int dy;
        let dy = -r;
        if (r > 181) {
            return;
        }
        while(dy < (r + 1)) {
            do Screen.drawLine(x-Math.sqrt((r*r)-(dy*dy)),y + dy,x+Math.sqrt((r*r)-(dy*dy)),y + dy);
            let dy = dy + 1;
        }
        return;
    }
}