Invert Color Cycles Node

as with the HSV node the OSL code is relying on the (yet to be implemented) autorename.

Also the svm code could use mix (svm_lerp) instead:
 32 . float3 color_inv = make_float3(1.0f, 1.0f, 1.0f) - color;
 35 . . stack_store_float3(stack, out_color, svm_lerp(color_inv, color, factor));

I have a feeling that each node 'program' should have the least program as possible. I'll see with Brecht later.
But overall I don't know if that's any fast. And apart from that I think we will need this kind of function to move to a library if multiple functions linked in are not a problem.

intern/cycles/kernel/svm/svm_invert.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2011, Blender Foundation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+CCL_NAMESPACE_BEGIN
+
+__device float invert(float color, float factor)
+{
+	return factor*(1.0f - color) + (1.0f - factor) * color;
+}
+
+__device void svm_node_invert(ShaderData *sd, float *stack, uint in_fac, uint in_color, uint out_color)
+{
+	float factor = stack_load_float(stack, in_fac);
+	float3 color = stack_load_float3(stack, in_color);
+
+	color.x = invert(color.x, factor);
+	color.y = invert(color.y, factor);
+	color.z = invert(color.z, factor);
+
+	if (stack_valid(out_color))
+		stack_store_float3(stack, out_color, color);
+}
+
+CCL_NAMESPACE_END
+