draw.ts

namespace asteroids {
    export class gfx {
        // Avoiding img.drawLine due to https://github.com/microsoft/pxt-arcade/issues/3344
        // Issue fixed in https://github.com/microsoft/pxt-common-packages/pull/1240

        // Here is a nice compact line drawing algorithm found in this amazing paper
        // (section 1.7): http://members.chello.at/~easyfilter/Bresenham.pdf
        public static drawLine(img: Image, p0: Vec2, p1: Vec2, color: number) {
            let x0 = fx.floor(p0.x);
            let y0 = fx.floor(p0.y);
            const x1 = fx.floor(p1.x);
            const y1 = fx.floor(p1.y);
            const dx =  Fx.abs(Fx.sub(x1, x0));
            const sx = x0 < x1 ? Fx.oneFx8 : Fx8(-1);
            const dy = Fx.neg(Fx.abs(Fx.sub(y1, y0)));
            const sy = y0 < y1 ? Fx.oneFx8 : Fx8(-1);
            let err = Fx.add(dx, dy);
            while (true) {
                img.setPixel(Fx.toInt(x0), Fx.toInt(y0), color);
                if (x0 == x1 && y0 == y1) break;
                let e2 = Fx.mul(Fx.twoFx8, err);
                if (e2 >= dy) {
                    err = Fx.add(err, dy);
                    x0 = Fx.add(x0, sx);
                }
                if (e2 <= dx) {
                    err = Fx.add(err, dx);
                    y0 = Fx.add(y0, sy);
                }
            }
        }
    }
}