From 3d082505f7ca720bd34b1311a2ae7bca5e20a5f0 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Tue, 4 Mar 2025 20:15:43 +0000
Subject: Have Camera keep an array of frustum plane definitions

Based on code from https://ktstephano.github.io/rendering/stratusgfx/aabbs
---
 gfx/gl/camera.cpp | 5 +++++
 gfx/gl/camera.h   | 7 +++++++
 2 files changed, 12 insertions(+)

(limited to 'gfx')

diff --git a/gfx/gl/camera.cpp b/gfx/gl/camera.cpp
index f03e85b..9e165fa 100644
--- a/gfx/gl/camera.cpp
+++ b/gfx/gl/camera.cpp
@@ -29,6 +29,11 @@ Camera::updateView()
 	view = glm::lookAt({}, forward, up);
 	viewProjection = projection * view;
 	inverseViewProjection = glm::inverse(viewProjection);
+	static constexpr auto PLANES = std::array {0, 1, 2} * std::array {1.F, -1.F};
+	std::ranges::transform(PLANES, frustumPlanes.begin(), [vpt = glm::transpose(viewProjection)](const auto & idxs) {
+		const auto [idx, sgn] = idxs;
+		return vpt[3] + (vpt[idx] * sgn);
+	});
 }
 
 Direction3D
diff --git a/gfx/gl/camera.h b/gfx/gl/camera.h
index 5c37744..d4fe6de 100644
--- a/gfx/gl/camera.h
+++ b/gfx/gl/camera.h
@@ -70,6 +70,12 @@ public:
 		return position;
 	}
 
+	[[nodiscard]] auto &
+	getFrustumPlanes() const
+	{
+		return frustumPlanes;
+	}
+
 	[[nodiscard]] std::array<GlobalPosition4D, 4> extentsAtDist(GlobalDistance) const;
 
 	[[nodiscard]] static Direction3D upFromForward(const Direction3D & forward);
@@ -84,4 +90,5 @@ private:
 	GlobalDistance near, far;
 	glm::mat4 view, projection;
 	glm::mat4 viewProjection, inverseViewProjection;
+	std::array<glm::vec4, 6> frustumPlanes;
 };
-- 
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