BresenhamLineDrawer.java

class BresenhamLineDrawer implements LineDrawer {
    private PixelSetter buffer;
    public BresenhamLineDrawer(PixelSetter buffer) {
        this.buffer = buffer;
    }

    @Override
    public void drawLine(int x1, int y1, int x2, int y2) {
        int deltaX = Math.abs(x2 - x1);
        int deltaY = Math.abs(y2 - y1);

        int x = x1;
        int y = y1;

        int sx = (int)Math.signum(x2 - x1);
        int sy = (int)Math.signum(y2 - y1);

        int p = 2*deltaY - deltaX;

        for (int i=0; i <= deltaX; i++) {
            buffer.setPixel(x, y);
            x += sx;

            if (p < 0) {
                p += 2*deltaY;
            }
            else {
                p += 2*deltaY - 2*deltaX;
                y += sy;
            }
        }
    }
}

FrameBufferWrapper.java

class FrameBufferWrapper implements PixelSetter {
    private Framebuffer framebuffer;
    public FrameBufferWrapper(Framebuffer framebuffer) {
        this.framebuffer = framebuffer;
    }

    @Override
    public void setPixel(int x, int y) {
        framebuffer.setPixel(x, y, Vec3.one);
    }
}

LineDrawer.java

interface LineDrawer {
    public void drawLine(int x1, int y1, int x2, int y2);
}

LineDrawerDecorator.java

class LineDrawerDecorator implements LineDrawer {
    private LineDrawer component;
    public LineDrawerDecorator(LineDrawer component) {
        this.component = component;
    }

    @Override
    public void drawLine(int x1, int y1, int x2, int y2) {
        component.drawLine(y1, x1, y2, x2); // swapped x and y
    }
}

PixelSetter.java

interface PixelSetter {
    public void setPixel(int x, int y);
}

PixelSetterDecorator.java

class PixelSetterDecorator implements PixelSetter {
    private PixelSetter component;
    public PixelSetterDecorator(PixelSetter component) {
        this.component = component;
    }

    @Override
    public void setPixel(int x, int y) {
        component.setPixel(y, x); // swapped x and y 
    }
}

Usage.java

int deltaX = Math.abs(x2 - x1);
int deltaY = Math.abs(y2 - y1);

PixelSetter buffer = new FrameBufferWrapper(framebuffer);
if (deltaY > deltaX) {
    buffer = new PixelSetterDecorator(buffer);
}

LineDrawer lineDrawer = new BresenhamLineDrawer(buffer);
if (deltaY > deltaX) {
    lineDrawer = new LineDrawerDecorator(lineDrawer);
}

lineDrawer.drawLine(x1, y1, x2, y2);