Class TCastleBehavior

Continuously occuring event, for various tasks.

Parameters

RemoveMe

Set this to rtRemove or rtRemoveAndFree to remove this component from Parent after this call finished. rtRemoveAndFree additionally will free this item. Initially it's rtNone when this method is called.

Event called right before rendering the parent TCastleTransform. Override this if you have to adjust the parent transformation strictly before the rendering.

Compared to adjusting the parent transformation in e.g. Update, adjusting the parent transformation here has advantages:

1. There's no 1-frame delay between moving the thing that causes the change (like camera) and updating the thing that reacts to it (like a transformation with a billboard).

2. We adjust transformation before rendering each occurrence of TCastleTransform in the viewport tree. This matters if given TCastleTransform may occur multiple times in the viewport tree, directly or through TCastleTransformReference.

3. We adjust transformation before each render, so things are OK if given TCastleTransform is present in multiple viewports (see https://castle-engine.io/multiple_viewports_to_display_one_world).

For example, adjusting the TCastleTransform done by the TCastleBillboard is done using this method. The transformation in this case is determined by the camera and parent's parent transformation. The transformation has to be applied without any delay (even a 1-frame delay would be visible, as artifacts caused by billboard not perfectly aligned with the camera would be visible – blending sort along camera direction in sort3D is not perfect if billboard doesn't exactly match camera direction). And the transformation with billboard may be present in multiple viewports and/or multiple times in the same viewport tree.

Parameters

CameraView

Current camera vectors, in world coordinates, used to render the scene now.

ParentParentWorldTransformation

World transformation of the parent of the parent of this behavior. The name is kind of convoluted, but consistent: When the parent of this behavior has exactly one parent TCastleTransform (not zero, not more) then ParentParentWorldTransformation.Transform is equivalent to Parent.Parent.WorldTransform.

Warning: this symbol is deprecated: Use ParentAfterAttach / ParentBeforeDetach or WorldAfterAttach / WorldBeforeDetach

Called after Parent changed, at the end of TCastleTransform.AddBehavior, TCastleTransform.RemoveBehavior.

Called after Parent changed, e.g. at the end of TCastleTransform.AddBehavior.

Called before Parent changed, e.g. at the beginning of TCastleTransform.RemoveBehavior.

This is also called at the destruction of behavior (more precisely from BeforeDestruction now). Even in this case, we guarantee that Parent is still valid during this call, and not in half-destroyed state. Before the actual destructor of TCastleBehavior we do BeforeParentDetach and BeforeWorldDetach and set Parent to Nil.

Called after Parent became part of World. Called only if ListenWorldChange is True.

Called before Parent stops being part of World. Called only if ListenWorldChange is True.

This is also called at the destruction of behavior (more precisely from BeforeDestruction now). Even in this case, we guarantee that Parent is still valid during this call, and not in half-destroyed state. Before the actual destructor of TCastleBehavior we do BeforeParentDetach and BeforeWorldDetach and set Parent to Nil.

Check can this behavior be added to NewParent. When this returns False, it has to set also ReasonWhyCannot. When overriding this, you can use e.g. this code to make sure we are the only behavior of given class:

function TCastleBillboard.CanAttachToParent(const NewParent: TCastleTransform;
  out ReasonWhyCannot: String): Boolean;
begin
  Result := inherited;
  if not Result then Exit;

  if NewParent.FindBehavior(TCastleBillboard) <> nil then
  begin
    ReasonWhyCannot := 'Only one TCastleBillboard behavior can be added to a given TCastleTransform';
    Result := false;
  end;
end;

This item has no description.

Reference to the root transformation (typically matching the TCastleViewport.Items value) corresponding to the parent of this behavior.

May be Nil if the behavior is not yet added to the parent TCastleTransform, or when the TCastleTransform is not yet part of the TCastleAbstractRootTransform (which means that TCastleTransform is not added to the viewport yet). You can use ListenWorldChange and override WorldBeforeDetach, WorldAfterAttach to be notified when this changes.

Parent TCastleTransform of this behavior. Change it by doing TCastleTransform.AddBehavior, TCastleTransform.RemoveBehavior.

Nil if this behavior is not yet added to a parent.

Set this to True to receive WorldBeforeDetach, WorldAfterAttach calls.