Draw particles only inside of primitive?

[mastmartelli]

I have this in my draw event:

if (!surface_exists(surf)) surf = surface_create(room_width, room_height);

//set surface as drawing target
surface_set_target(surf);

draw_clear_alpha(1, 0);

//draw particles to surface
part_system_drawit(global.partSys);

gpu_set_blendmode(bm_subtract);

with (oGrabberCenter) {
    //bucket primitive
    draw_primitive_begin(pr_trianglestrip);
    draw_vertex(bbox_left, bbox_bottom);
    draw_vertex(bbox_right, bbox_bottom);
    draw_vertex(bbox_left, bbox_top);
    draw_vertex(bbox_right, bbox_top);
    draw_primitive_end();
}

gpu_set_blendmode(bm_normal);
surface_reset_target();
draw_surface(surf, 0, 0);

This will draw the particles everywhere except inside of the primitive, is there anyway to do the opposite?

 

[davawen]

Substract the primitive from a clear surface, then substract the surface from the particle surface.