From 5b4a34cb8c272c96f94fc0d45684f675085587a6 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sat, 21 Feb 2026 00:50:31 +0000
Subject: Simplified Frustum

Don't need to differentiate between shadedBy by contains. The 5
plane/face variant is actually fine in both cases. For a perspective
projection, the near plane is essentially at the origin and is handled
by the left/right/top/bottom planes meeting. For the directional light
case (orthographic projection) the near plane is omitted as objects in
front of the clip space still cast shadows into it.
Also includes a fix the distance calculation to not add .w, don't know
where I got the idea this was right.
---
 game/terrain.cpp |  2 +-
 gfx/frustum.cpp  | 41 ++++++++++++-----------------------------
 gfx/frustum.h    |  7 ++-----
 3 files changed, 15 insertions(+), 35 deletions(-)

diff --git a/game/terrain.cpp b/game/terrain.cpp
index f10aac6..187d035 100644
--- a/game/terrain.cpp
+++ b/game/terrain.cpp
@@ -152,7 +152,7 @@ Terrain::shadows(const ShadowMapper & shadowMapper, const Frustum & frustum) con
 {
 	shadowMapper.landmess.use();
 	for (const auto & [surface, sab] : meshes) {
-		if (frustum.shadedBy(sab.aabb)) {
+		if (frustum.contains(sab.aabb)) {
 			glBindVertexArray(sab.vertexArray);
 			glDrawElements(GL_TRIANGLES, sab.count, GL_UNSIGNED_INT, nullptr);
 		}
diff --git a/gfx/frustum.cpp b/gfx/frustum.cpp
index 7050910..294fe5d 100644
--- a/gfx/frustum.cpp
+++ b/gfx/frustum.cpp
@@ -20,18 +20,6 @@ Frustum::updateView(const glm::mat4 & newView)
 
 bool
 Frustum::contains(const BoundingBox & aabb) const
-{
-	return boundByPlanes(aabb, FACES);
-}
-
-bool
-Frustum::shadedBy(const BoundingBox & aabb) const
-{
-	return boundByPlanes(aabb, FACES - 1);
-}
-
-bool
-Frustum::boundByPlanes(const BoundingBox & aabb, size_t nplanes) const
 {
 	static constexpr auto EXTENT_CORNER_IDXS = [] {
 		using Extent = GlobalPosition3D BoundingBox::*;
@@ -48,27 +36,21 @@ 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 contains(corners, nplanes, 0);
+	return contains(corners, 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);
+	return contains(std::array {RelativePosition4D {(point - position), 1.F}}, size);
 }
 
 bool
-Frustum::contains(const std::span<const RelativePosition4D> points, const size_t nplanes, RelativeDistance size) const
+Frustum::contains(const std::span<const RelativePosition4D> points, RelativeDistance size) const
 {
-	return std::ranges::none_of(std::span(planes).subspan(0, nplanes), [&points, size](const auto & frustumPlane) {
+	return std::ranges::none_of(planes, [&points, size](const auto & frustumPlane) {
 		return (std::ranges::all_of(points, [&frustumPlane, size](const auto & point) {
-			const auto distanceFromPlane = glm::dot(frustumPlane, point) + frustumPlane.w;
+			const auto distanceFromPlane = glm::dot(frustumPlane, point);
 			return distanceFromPlane < -size;
 		}));
 	});
@@ -79,10 +61,11 @@ Frustum::updateCache()
 {
 	viewProjection = projection * view;
 	inverseViewProjection = glm::inverse(viewProjection);
-	std::ranges::transform(PLANES, planes.begin(), [vpt = glm::transpose(viewProjection)](const auto & idxs) {
-		const auto [idx, sgn] = idxs;
-		const auto plane = vpt[3] + (vpt[idx] * sgn);
-		const auto mag = glm::length(plane.xyz());
-		return plane / mag;
-	});
+	std::ranges::transform(PLANES | std::views::take(planes.size()), planes.begin(),
+			[vpt = glm::transpose(viewProjection)](const auto & idxs) {
+				const auto [idx, sgn] = idxs;
+				const auto plane = vpt[3] + (vpt[idx] * sgn);
+				const auto mag = glm::length(plane.xyz());
+				return plane / mag;
+			});
 }
diff --git a/gfx/frustum.h b/gfx/frustum.h
index 1493a36..cd4cbe1 100644
--- a/gfx/frustum.h
+++ b/gfx/frustum.h
@@ -33,14 +33,11 @@ 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;
+	static constexpr size_t FACES = 5;
 	void updateCache();
-	[[nodiscard]] bool boundByPlanes(const BoundingBox &, size_t nplanes) const;
-	[[nodiscard]] bool contains(std::span<const RelativePosition4D>, size_t nplanes, RelativeDistance) const;
+	[[nodiscard]] bool contains(std::span<const RelativePosition4D>, RelativeDistance) const;
 
 	GlobalPosition3D position;
 	glm::mat4 view, projection;
-- 
cgit v1.3