1 files changed, 18 insertions, 0 deletions
diff --git a/source/blender/draw/engines/overlay/shaders/outline_prepass_frag.glsl b/source/blender/draw/engines/overlay/shaders/outline_prepass_frag.glsl
new file mode 100644
index 00000000000..5d6c4881b5b
--- /dev/null
+++ b/source/blender/draw/engines/overlay/shaders/outline_prepass_frag.glsl
@@ -0,0 +1,18 @@
+
+/* Should be 2 bits only [0..3]. */
+uniform int outlineId;
+
+flat in int objectId;
+
+/* using uint because 16bit uint can contain more ids than int. */
+out uint outId;
+
+/* Replace top 2 bits (of the 16bit output) by outlineId.
+ * This leaves 16K different IDs to create outlines between objects.
+ * SHIFT = (32 - (16 - 2)) */
+#define SHIFT 18u
+
+void main()
+{
+  outId = (uint(outlineId) << 14u) | ((uint(objectId) << SHIFT) >> SHIFT);
+}