From 35f73ba19deb13ff1971983bc9c21fe342c91214 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Wed, 28 Dec 2022 14:04:01 +0000
Subject: Reduce camera extents to the point they cross the sea floor boundary

---
 gfx/gl/camera.cpp | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/gfx/gl/camera.cpp b/gfx/gl/camera.cpp
index ff706e7..5ae5fb0 100644
--- a/gfx/gl/camera.cpp
+++ b/gfx/gl/camera.cpp
@@ -1,4 +1,5 @@
 #include "camera.h"
+#include <glm/gtx/intersect.hpp> // IWYU pragma: keep
 #include <glm/gtx/transform.hpp> // IWYU pragma: keep
 #include <maths.h>
 #include <ray.hpp>
@@ -35,6 +36,14 @@ Camera::upFromForward(const glm::vec3 & forward)
 std::array<glm::vec3, 4>
 Camera::extentsAtDist(const float dist) const
 {
+	const auto adjustToSeafloor = [this](glm::vec3 & target) {
+		const auto vec = glm::normalize(target - position);
+		constexpr glm::vec3 seafloor {0, 0, -1.5};
+		float outdist;
+		if (glm::intersectRayPlane(position, vec, seafloor, ::up, outdist)) {
+			target = vec * outdist + position;
+		}
+	};
 	const auto depth = -(2.f * (dist - near) * far) / (dist * (near - far)) - 1.f;
 	static constexpr const std::array extents {-1.F, 1.F};
 	std::array<glm::vec3, 4> out {};
@@ -44,7 +53,11 @@ Camera::extentsAtDist(const float dist) const
 			const glm::vec4 in {x, y, depth, 1.f};
 
 			const auto out = inverseViewProjection * in;
-			*outitr++ = out / out.w;
+			*outitr = out / out.w;
+			if (outitr->z < -1.5f) {
+				adjustToSeafloor(*outitr);
+			}
+			outitr++;
 		}
 	}
 	return out;
-- 
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