Fixed the issue that an object disappeared in a multi-material painting gizmo when the object was almost completely sunk under the bed.

Object disappearance was caused by calling glPolygonOffset for rendered triangles in the multi-material painting gizmo to resolve z-fighting between painted triangles and contours around selected areas using seed/bucket fill.

resources/shaders/mm_contour.fs

@@ -1,6 +1,11 @@
 #version 110
 
+const float EPSILON = 0.0001;
+
 void main()
 {
     gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
+    // Values inside depth buffer for fragments of the contour of a selected area are offset
+    // by small epsilon to solve z-fighting between painted triangles and contour lines.
+    gl_FragDepth = gl_FragCoord.z - EPSILON;
 }