From 8496bd9720888701267f8f39a2f3a74a65f1006f Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sun, 15 Feb 2026 00:50:02 +0000
Subject: Support for testing if a point/sphere is within a Frustum

Use case is the sphere approximating a scenery item such as a tree.
---
 gfx/frustum.cpp | 24 +++++++++++++++++++++---
 gfx/frustum.h   |  4 ++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/gfx/frustum.cpp b/gfx/frustum.cpp
index faa676d..5c85ac0 100644
--- a/gfx/frustum.cpp
+++ b/gfx/frustum.cpp
@@ -48,9 +48,27 @@ Frustum::boundByPlanes(const BoundingBox & aabb, size_t nplanes) const
 			= EXTENT_CORNER_IDXS * [relativeAabb = aabb - position](auto idxs) -> glm::vec4 {
 		return {(relativeAabb.*(idxs.x)).x, (relativeAabb.*(idxs.y)).y, (relativeAabb.*(idxs.z)).z, 1.F};
 	};
-	return std::ranges::none_of(std::span(planes).subspan(0, nplanes), [&corners](const auto & frustumPlane) {
-		return (std::ranges::all_of(corners, [&frustumPlane](const auto & corner) {
-			return glm::dot(frustumPlane, corner) < 0.F;
+	return contains(corners, nplanes, 0);
+}
+
+bool
+Frustum::contains(GlobalPosition3D point, RelativeDistance size) const
+{
+	return contains(std::array {RelativePosition4D {(point - position), 1.F}}, FACES, size);
+}
+
+bool
+Frustum::shadedBy(GlobalPosition3D point, RelativeDistance size) const
+{
+	return contains(std::array {RelativePosition4D {(point - position), 1.F}}, FACES - 1, size);
+}
+
+bool
+Frustum::contains(const std::span<const RelativePosition4D> points, const size_t nplanes, RelativeDistance size) const
+{
+	return std::ranges::none_of(std::span(planes).subspan(0, nplanes), [&points, size](const auto & frustumPlane) {
+		return (std::ranges::all_of(points, [&frustumPlane, size](const auto & corner) {
+			return glm::dot(frustumPlane, corner) < -size;
 		}));
 	});
 }
diff --git a/gfx/frustum.h b/gfx/frustum.h
index a2d90e9..1493a36 100644
--- a/gfx/frustum.h
+++ b/gfx/frustum.h
@@ -4,6 +4,7 @@
 #include "config/types.h"
 #include <array>
 #include <glm/mat4x4.hpp>
+#include <span>
 
 class Frustum {
 public:
@@ -31,12 +32,15 @@ public:
 
 	using BoundingBox = AxisAlignedBoundingBox<GlobalDistance>;
 	[[nodiscard]] bool contains(const BoundingBox &) const;
+	[[nodiscard]] bool contains(GlobalPosition3D, RelativeDistance size = 0) const;
 	[[nodiscard]] bool shadedBy(const BoundingBox &) const;
+	[[nodiscard]] bool shadedBy(GlobalPosition3D, RelativeDistance size = 0) const;
 
 protected:
 	static constexpr size_t FACES = 6;
 	void updateCache();
 	[[nodiscard]] bool boundByPlanes(const BoundingBox &, size_t nplanes) const;
+	[[nodiscard]] bool contains(std::span<const RelativePosition4D>, size_t nplanes, RelativeDistance) const;
 
 	GlobalPosition3D position;
 	glm::mat4 view, projection;
-- 
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