Index: src_plugins/hid_gtk2_gl/gtkhid-gl.c
===================================================================
--- src_plugins/hid_gtk2_gl/gtkhid-gl.c	(revision 8842)
+++ src_plugins/hid_gtk2_gl/gtkhid-gl.c	(revision 8843)
@@ -314,15 +314,15 @@
 		stencil_bit = hidgl_assign_clear_stencil_bit();	/* Get a new (clean) bitplane to stencil with */
 		break;
 
-	case HID_MASK_SET:
-		/* Write '1' to the stencil buffer where the solder-mask should not be drawn ("transparent", "cutout"). */
+	case HID_MASK_CLEAR:
+		/* Write '0' to the stencil buffer where the solder-mask should not be drawn ("transparent", "cutout"). */
 		glStencilFunc(GL_ALWAYS, stencil_bit, stencil_bit);	/* Always pass stencil test, write stencil_bit */
 		glStencilMask(stencil_bit);	/* Only write to our subcompositing stencil bitplane */
 		glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);	/* Stencil pass => replace stencil value (with 1) */
 		break;
 
-	case HID_MASK_CLEAR:
-		/* Write '0' to the stencil buffer where the solder-mask should not be drawn. */
+	case HID_MASK_SET:
+		/* Write '1' to the stencil buffer where the solder-mask should be drawn ("red", "solid"). */
 		glStencilFunc(GL_ALWAYS, stencil_bit, stencil_bit);	/* Always pass stencil test, write stencil_bit */
 		glStencilMask(stencil_bit);	/* Only write to our subcompositing stencil bitplane */
 		glStencilOp(GL_KEEP, GL_KEEP, GL_ZERO);	/* Stencil pass => replace stencil value (with 1) */
@@ -331,7 +331,7 @@
 	case HID_MASK_AFTER:
 		/* Drawing operations as masked to areas where the stencil buffer is '0' */
 		glColorMask(1, 1, 1, 1);		/* Enable drawing of r, g, b & a */
-		glStencilFunc(GL_NOTEQUAL, 0, stencil_bit);	/* Draw only where our bit of the stencil buffer is clear */
+		glStencilFunc(GL_GEQUAL, 0, stencil_bit);	/* Draw only where our bit of the stencil buffer is clear */
 		glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);	/* Stencil buffer read only */
 		break;
 
Index: src_plugins/hid_gtk2_gl/hidgl.c
===================================================================
--- src_plugins/hid_gtk2_gl/hidgl.c	(revision 8842)
+++ src_plugins/hid_gtk2_gl/hidgl.c	(revision 8843)
@@ -585,6 +585,7 @@
 	int vertex_count = 0;
 	pcb_pline_t *contour;
 	struct do_hole_info info;
+	int stencil_bit;
 
 	info.scale = scale;
 	global_scale = scale;
@@ -594,6 +595,12 @@
 		return;
 	}
 
+	stencil_bit = hidgl_assign_clear_stencil_bit();
+	if (!stencil_bit) {
+		printf("hidgl_fill_pcb_polygon: No free stencil bits, aborting polygon\n");
+		return;
+	}
+
 	/* Flush out any existing geoemtry to be rendered */
 	hidgl_flush_triangles(&buffer);
 
@@ -609,14 +616,42 @@
 	gluTessCallback(info.tobj, GLU_TESS_COMBINE, (_GLUfuncptr) myCombine);
 	gluTessCallback(info.tobj, GLU_TESS_ERROR, (_GLUfuncptr) myError);
 
+	glPushAttrib(GL_STENCIL_BUFFER_BIT);	/* Save the write mask etc.. for final restore */
+	glEnable(GL_STENCIL_TEST);
+	glPushAttrib(GL_STENCIL_BUFFER_BIT |	/* Resave the stencil write-mask etc.., and */
+							 GL_COLOR_BUFFER_BIT);	/* the colour buffer write mask etc.. for part way restore */
+	glStencilMask(stencil_bit);		/* Only write to our stencil bit */
+	glStencilFunc(GL_ALWAYS, stencil_bit, stencil_bit);	/* Always pass stencil test, ref value is our bit */
+	glColorMask(0, 0, 0, 0);			/* Disable writting in color buffer */
+
+	glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);	/* Stencil pass => replace stencil value */
+
+	/* Drawing operations now set our reference bit in the stencil buffer */
+
 	pcb_r_search(poly->Clipped->contour_tree, clip_box, NULL, do_hole, &info, NULL);
 	hidgl_flush_triangles(&buffer);
 
+	glPopAttrib();								/* Restore the colour and stencil buffer write-mask etc.. */
+
+	glStencilOp(GL_KEEP, GL_KEEP, GL_INVERT);	/* This allows us to toggle the bit on any subcompositing bitplane */
+	/* If the stencil test has passed, we know that bit is 0, so we're */
+	/* effectively just setting it to 1. */
+
+	glStencilFunc(GL_GEQUAL, 0, assigned_bits);	/* Pass stencil test if all assigned bits clear, */
+	/* reference is all assigned bits so we set */
+	/* any bits permitted by the stencil writemask */
+
+	/* Drawing operations as masked to areas where the stencil buffer is '0' */
+
 	/* Draw the polygon outer */
 	tesselate_contour(info.tobj, poly->Clipped->contours, info.vertices, scale);
 	hidgl_flush_triangles(&buffer);
 
+	/* Unassign our stencil buffer bit */
+	hidgl_return_stencil_bit(stencil_bit);
 
+	glPopAttrib();								/* Restore the stencil buffer write-mask etc.. */
+
 	gluDeleteTess(info.tobj);
 	myFreeCombined();
 	free(info.vertices);