Arc drawing issue - poly drawing in black (not alpha)

[graaaeme10]

Hi there, I'm using this code to draw arcs, which should draw a grey arc first then a red arc over top, in the second half of the arc:


void plainArc(int x, int y, int r1, int r2, uint16_t a1, uint16_t a2, uint32_t color, byte options) {

 int ra = r2 * 2;

 GD.SaveContext();

 GD.ColorMask(0, 0, 0, 1);

 GD.Clear();

 GD.Begin(POINTS);



 PAINT_ALPHA();

 GD.PointSize(r2 * 8);

 GD.Vertex2f(8 * x, 8 * y);



 CLEAR_ALPHA();

 GD.PointSize(r1 * 8);

 GD.Vertex2f(8 * x, 8 * y);

 int px, py;

 GD.Begin(LINES);

 GD.LineWidth(12);

 GD.polar(px, py, ra, a1);

 GD.Vertex2f(8 * x, 8 * y);

 GD.Vertex2f(8 * (x + px), 8 * (y + py));

 GD.polar(px, py, ra, a2);

 GD.Vertex2f(8 * x, 8 * y);

 GD.Vertex2f(8 * (x + px), 8 * (y + py));

 Poly po;

 po.begin();

 po.v(8 * x, 8 * y);

 for (int i = 0; i < 5; i++) {

   int rx, ry;

   GD.polar(rx, ry, ra, a2 + ((65536 - a2 + a1) / 4) * i);

   po.v(8 * (x + rx), 8 * (y + ry));

 }

 po.draw();

 GD.RestoreContext();



 GD.SaveContext();

 DRAW_IN_ALPHA();


 GD.Begin(RECTS);

 GD.ColorRGB(color);

 GD.Vertex2f(8 * (x - r2), 8 * (y - r2));

 GD.Vertex2f(8 * (x + r2), 8 * (y + r2));

 GD.RestoreContext();



 

}

plainArc(400, 250, 123, 126, 8192, 57344, 0x303030, 0);

plainArc(400, 250, 122, 127, 32768, 57344, 0xFF0000, 1);

However it only displays the red arc, it would appear that the polygon that is drawn in the alpha channel to mask off the non-drawn portion of the arc is masking off the next arc to be drawn. I would have thought with saving and restoring the context, this wouldn't be an issue.
EDIT: It would appear the poly is just drawing itself in black, and not removing from the alpha channel?

Any help would be appreciated, cheers.