And why not add the ability to draw lines into our bitmap too:


[Linked Image from i.imgur.com]

Use a drawline routine from the hp9845 driver and make some changes:

Code
//void hp9845ct_base_state::draw_line(unsigned x0 , unsigned y0 , unsigned x1 , unsigned y1)
void drawline(int x0 , int y0 , int x1 , int y1, u32 pixelval)
{
        int dx, dy, sx, sy, x, y, err, e2;

        // draw line, vector generator uses Bresenham's algorithm
        x = x0;
        y = y0;
        dx = abs((int) (x1 - x));
        sx = x < x1 ? 1 : -1;   // actually always 1 because of normalization
        dy = abs((int) (y1 - y));
        sy = y < y1 ? 1 : -1;
        err = (dx > dy ? dx : -dy) / 2;

        for(;;){
//                plot(x, y, BIT(m_gv_line_type_mask, 15));
//               update_line_pattern();

		if (!((x<0) || (x >= m_lp_bitmap->width()) || (y<0) || (y >= m_lp_bitmap->height()))) 
					m_lp_bitmap->pix32(y,x) = pixelval;

                if (x == x1 && y == y1) break;

                e2 = err;
                if (e2 > -dx) {
                        err -= dy;
                        x += sx;
                }
                if (e2 < dy) {
                        err += dx;
                        y += sy;
                }
        }
}


and make some spokes:

Code
function drawcirclespokes(cx,cy,size,step,color) 
for i=0,360,step do 
  manager:machine().lp[1]:drawline(math.floor(cx),math.floor(cy),math.floor(cx+size*math.cos(i/360*2*math.pi)),math.floor(cy+size*math.sin(i/360*2*math.pi)),color) 
  manager:machine().lp[1]:drawline(math.floor(cx+size*math.cos(i/360*2*math.pi)),math.floor(cy+size*math.sin(i/360*2*math.pi)),
math.floor(cx+size*math.cos((i+step)/360*2*math.pi)),math.floor(cy+size*math.sin((i+step)/360*2*math.pi)),color)
 end
end

drawcirclespokes(200,792,150,360/36,0)
drawcirclespokes(0,0,360,360/36,0)
drawcirclespokes(8.5*120,0,360,360/36,0)
drawcirclespokes(9.0*120,792,360,360/36,0)