Support for clearing HDRI background

[kevinfoley]

Describe your feature request

BlenderProc offers a method set_world_background_hdr_img() which we can use to load an HDRI image as the scene background. This method creates new nodes, but does not remove previous nodes. If we use the function repeatedly (e.g. to load different background images for different camera angles), unused nodes from previous backgrounds remain in the scene (they will be overlapping in the Shader Editor, so move the nodes around to reveal unused leftover nodes). This could be considered a memory leak and may be problematic if we load many different backgrounds.

Perhaps there should be a function for clearing any previous background HDR image, which we could call manually and would also be automatically called by set_world_background_hdr_img().

Describe a possible solution

No response

[kevinfoley]

This seems to work for our use case, but I am not certain how robust of a solution it is:

def clear_world_background():
    """
    Clears any custom world background, restoring the default solid color.
    """
    world = bpy.context.scene.world
    nodes = world.node_tree.nodes

    # remove all nodes
    for node in nodes:
        if node.bl_idname not in ["ShaderNodeBackground", "ShaderNodeOutputWorld"]:
            nodes.remove(node)

[kevinfoley]

This is only tangentially related, but I'll note it here in case it's helpful to others in the future. For object materials, we similarly have found that material.set_principled_shader_value("Base Color", image) leaks memory because it creates a new node and does not remove the previous node. The fix for that is:

previous_nodes = material.get_nodes_with_type("ShaderNodeTexImage")
for previous_node in previous_nodes:
    material.remove_node(previous_node)