material: Adds _cogl_material_pre_paint_for_layer

This is a counter part for _cogl_material_layer_pre_paint which takes a
layer index instead of a direct CoglMaterialLayer pointer. The aim is to
phase out code that directly iterates the internal layer pointers of a
material since the layer pointers can change if any property of any
layer is changed making direct layer pointers very fragile.

cogl/cogl-material-private.h

@@ -606,6 +606,15 @@ _cogl_material_layer_has_user_matrix (CoglMaterialLayer *layer);
 void
 _cogl_material_layer_pre_paint (CoglMaterialLayer *layerr);
 
+/*
+ * Calls the pre_paint method on the layer texture if there is
+ * one. This will determine whether mipmaps are needed based on the
+ * filter settings.
+ */
+void
+_cogl_material_pre_paint_for_layer (CoglMaterial *material,
+                                    int layer_id);
+
 /*
  * CoglMaterialFlushFlag:
  * @COGL_MATERIAL_FLUSH_FALLBACK_MASK: The fallback_layers member is set to

cogl/cogl-material.c

@@ -5237,6 +5237,14 @@ _cogl_material_layer_pre_paint (CoglMaterialLayer *layer)
     }
 }
 
+void
+_cogl_material_pre_paint_for_layer (CoglMaterial *material,
+                                    int layer_id)
+{
+  CoglMaterialLayer *layer = _cogl_material_get_layer (material, layer_id);
+  _cogl_material_layer_pre_paint (layer);
+}
+
 CoglMaterialFilter
 cogl_material_layer_get_min_filter (CoglMaterialLayer *layer)
 {