Implement visibility range and dependencies.

This commit adds the following properties to GeometryInstance3D: `visibility_range_begin`,
`visibility_range_begin_margin`, `visibility_range_end`, `visibility_range_end_margin`.

Together they define a range in which the GeometryInstance3D will be visible from the camera,
taking hysteresis into account for state changes. A begin or end value of 0 will be ignored,
so the visibility range can be open-ended in both directions.

This commit also adds the `visibility_parent` property to 'Node3D'.
Which defines the visibility parents of the node and its subtree (until
another parent is defined).

Visual instances with a visibility parent will only be visible when the parent, and all of its
ancestors recursively, are hidden because they are closer to the camera than their respective
`visibility_range_begin` thresholds.

Combining visibility ranges and visibility parents users can set-up a quick HLOD system
that shows high detail meshes when close (i.e buildings, trees) and merged low detail meshes
for far away groups (i.e. cities, woods).

1 files changed, 4 insertions, 0 deletions

diff --git a/servers/rendering/renderer_viewport.cpp b/servers/rendering/renderer_viewport.cpp
index 21f849e822..34bdb15c62 100644
--- a/servers/rendering/renderer_viewport.cpp
+++ b/servers/rendering/renderer_viewport.cpp
@@ -824,6 +824,10 @@ void RendererViewport::viewport_set_scenario(RID p_viewport, RID p_scenario) {
 	Viewport *viewport = viewport_owner.getornull(p_viewport);
 	ERR_FAIL_COND(!viewport);
 
+	if (viewport->scenario.is_valid()) {
+		RSG::scene->scenario_remove_viewport_visibility_mask(viewport->scenario, p_viewport);
+	}
+
 	viewport->scenario = p_scenario;
 	if (viewport->use_occlusion_culling) {
 		RendererSceneOcclusionCull::get_singleton()->buffer_set_scenario(p_viewport, p_scenario);