Fix layer nav operator

4.0.1

- fixed: layer nav operator on page up/down

utils.py

@@ -162,6 +162,33 @@ def layer_active_index(gpl):
     '''
     return next((i for i, l in enumerate(gpl) if l == gpl.active), None)
 
+def get_top_layer_from_group(gp, group):
+    upper_layer = None
+    for layer in gp.layers:
+        if layer.parent_group == group:
+            upper_layer = layer
+    return upper_layer
+
+def get_closest_active_layer(gp):
+    '''Get active layer from GP object, getting upper layer if in group
+    if a group is active, return the top layer of this group
+    if group is active but no layer in it, return None
+    '''
+
+    if gp.layers.active:
+        return gp.layers.active
+    ## No active layer, return active from group (can be None !)
+    return get_top_layer_from_group(gp, gp.layer_groups.active)
+
+def closest_layer_active_index(gp, fallback_index=0):
+    '''Get active layer index from GP object, getting upper layer if in group
+    if a group is active, return index at the top layer of this group
+    if group is active but no layer in it, return fallback_index (0 by default, stack bottom)'''
+    closest_active_layer = get_closest_active_layer(gp)
+    if closest_active_layer:
+        return next((i for i, l in enumerate(gp.layers) if l == closest_active_layer), fallback_index)
+    return fallback_index
+
 ## Check for nested lock
 def is_locked(stack_item):
     '''Check if passed stack item (layer or group) is locked
@@ -1200,6 +1227,38 @@ def iterate_selector(zone, attr, state, info_attr = None, active_access='active'
 
         return info, bottom
 
+def iterate_active_layer(gpd, state):
+    '''Iterate active GP layer in stack
+    gpd: Grease Pencil Data
+    '''
+    layers = gpd.layers
+    l_count = len(layers)
+    
+    if state: # swap
+        # info = None
+        # bottom = None
+        
+        ## Get active layer index
+        active_index = closest_layer_active_index(gpd, fallback_index=None)
+        if active_index == None:
+            ## fallback to first layer if nothing found
+            gpd.layers.active = layers[0]
+            return
+
+        target_index = active_index + state
+        new_index = target_index % l_count
+
+        ## set active layer        
+        gpd.layers.active = layers[new_index]
+
+        if target_index == l_count:
+            bottom = 1 # bottom reached, cycle to first
+        elif target_index < 0:
+            bottom = -1 # up reached, cycle to last
+
+        # info = gpd.layers.active.name
+        # return info, bottom
+
 # -----------------
 ### Curve handle
 # -----------------