material: Don't prune ancestry if it owns some layers1.4.0

Each time a material property changes we look to see if any of its
ancestry has become redundant and if so we prune that redundant
ancestry.

There was a problem with the logic that handles this though because we
weren't considering that a material which is a layer state authority may
still defer to ancestors to define the state of individual layers.

For example a material that derives from a parent with 5 layers can
become a STATE_LAYERS authority by simply changing it's ->n_layers count
to 4 and in that case it can still defer to its ancestors to define the
state of those 4 layers.

This patch checks first if a material is a layer state authority and if
so only tries to prune its ancestry if it also *owns* all the individual
layers it depends on. (I.e. if g_list_length
(material->layer_differences) != material->n_layers then it's not safe
to try pruning its ancestry!)

http://bugzilla-attachments.gnome.org/attachment.cgi?id=170907

1 files changed, 21 insertions, 0 deletions

diff --git a/cogl/cogl-material.c b/cogl/cogl-material.c
index 216914e2..985ebe2d 100644
--- a/cogl/cogl-material.c
+++ b/cogl/cogl-material.c
@@ -3537,6 +3537,27 @@ _cogl_material_prune_redundant_ancestry (CoglMaterial *material)
 {
   CoglMaterial *new_parent = _cogl_material_get_parent (material);
 
+  /* Before considering pruning redundant ancestry we check if this
+   * material is an authority for layer state and if so only consider
+   * reparenting if it *owns* all the layers it depends on. NB: A
+   * material can be be a STATE_LAYERS authority but it may still
+   * defer to its ancestors to define the state for some of its
+   * layers.
+   *
+   * For example a material that derives from a parent with 5 layers
+   * can become a STATE_LAYERS authority by simply changing it's
+   * ->n_layers count to 4 and in that case it can still defer to its
+   * ancestors to define the state of those 4 layers.
+   *
+   * If a material depends on any ancestors for layer state then we
+   * immediatly bail out.
+   */
+  if (material->differences & COGL_MATERIAL_STATE_LAYERS)
+    {
+      if (material->n_layers != g_list_length (material->layer_differences))
+        return;
+    }
+
   /* walk up past ancestors that are now redundant and potentially
    * reparent the material. */
   while (_cogl_material_get_parent (new_parent) &&