From 4a21e9e32525fe23915db97f3439cae780994118 Mon Sep 17 00:00:00 2001
From: Daniel Karbach <daniel.karbach@localhorst.tv>
Date: Mon, 9 Mar 2015 17:42:41 +0100
Subject: [PATCH] don't render chunk that are outside clip space

---
 src/chunk.cpp    |  3 +--
 src/chunk.hpp    |  2 ++
 src/geometry.cpp | 38 ++++++++++++++++++++++++++++++++++++++
 src/geometry.hpp |  2 ++
 src/shader.hpp   |  4 ++++
 src/world.cpp    |  8 ++++++--
 6 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/src/chunk.cpp b/src/chunk.cpp
index a485bfb..514431c 100644
--- a/src/chunk.cpp
+++ b/src/chunk.cpp
@@ -43,8 +43,7 @@ bool Chunk::Intersection(
 	float *dist,
 	glm::vec3 *normal) const {
 	{ // rough check
-		const AABB bb{{0, 0, 0}, {Width(), Height(), Depth()}};
-		if (!blank::Intersection(ray, bb, M)) {
+		if (!blank::Intersection(ray, Bounds(), M)) {
 			return false;
 		}
 	}
diff --git a/src/chunk.hpp b/src/chunk.hpp
index 185b3ea..b625a17 100644
--- a/src/chunk.hpp
+++ b/src/chunk.hpp
@@ -26,6 +26,8 @@ public:
 	static glm::vec3 Extent() { return glm::vec3(Width(), Height(), Depth()); }
 	static constexpr int Size() { return Width() * Height() * Depth(); }
 
+	static AABB Bounds() { return AABB{ { 0, 0, 0 }, { Width(), Height(), Depth() } }; }
+
 	static constexpr bool InBounds(const glm::vec3 &pos) {
 		return
 			pos.x >= 0 && pos.x < Width() &&
diff --git a/src/geometry.cpp b/src/geometry.cpp
index df48ad3..44217e9 100644
--- a/src/geometry.cpp
+++ b/src/geometry.cpp
@@ -126,4 +126,42 @@ bool Intersection(
 	return true;
 }
 
+bool CullTest(const AABB &box, const glm::mat4 &MVP) {
+	// transform corners into clip space
+	glm::vec4 corners[8] = {
+		{ box.min.x, box.min.y, box.min.z, 1.0f },
+		{ box.min.x, box.min.y, box.max.z, 1.0f },
+		{ box.min.x, box.max.y, box.min.z, 1.0f },
+		{ box.min.x, box.max.y, box.max.z, 1.0f },
+		{ box.max.x, box.min.y, box.min.z, 1.0f },
+		{ box.max.x, box.min.y, box.max.z, 1.0f },
+		{ box.max.x, box.max.y, box.min.z, 1.0f },
+		{ box.max.x, box.max.y, box.max.z, 1.0f },
+	};
+	for (glm::vec4 &corner : corners) {
+		corner = MVP * corner;
+		corner /= corner.w;
+	}
+
+	int hits[6] = { 0, 0, 0, 0, 0, 0 };
+
+	// check how many corners lie outside
+	for (const glm::vec4 &corner : corners) {
+		if (corner.x >  1.0f) ++hits[0];
+		if (corner.x < -1.0f) ++hits[1];
+		if (corner.y >  1.0f) ++hits[2];
+		if (corner.y < -1.0f) ++hits[3];
+		if (corner.z >  1.0f) ++hits[4];
+		if (corner.z < -1.0f) ++hits[5];
+	}
+
+	// if all corners are outside any given clip plane, the test is true
+	for (int hit : hits) {
+		if (hit == 8) return true;
+	}
+
+	// otherwise the box might still get culled completely, but can't say for sure ;)
+	return false;
+}
+
 }
diff --git a/src/geometry.hpp b/src/geometry.hpp
index d74e08e..9a9690b 100644
--- a/src/geometry.hpp
+++ b/src/geometry.hpp
@@ -32,6 +32,8 @@ bool Intersection(
 	float *dist = nullptr,
 	glm::vec3 *normal = nullptr);
 
+bool CullTest(const AABB &box, const glm::mat4 &MVP);
+
 }
 
 #endif
diff --git a/src/shader.hpp b/src/shader.hpp
index 195376c..ea5b844 100644
--- a/src/shader.hpp
+++ b/src/shader.hpp
@@ -75,6 +75,10 @@ public:
 	void SetVP(const glm::mat4 &v, const glm::mat4 &p);
 	void SetMVP(const glm::mat4 &m, const glm::mat4 &v, const glm::mat4 &p);
 
+	const glm::mat4 &Projection() const { return projection; }
+	const glm::mat4 &View() const { return view; }
+	const glm::mat4 &GetVP() const { return vp; }
+
 private:
 	Program program;
 
diff --git a/src/world.cpp b/src/world.cpp
index 216f3a2..7f30d71 100644
--- a/src/world.cpp
+++ b/src/world.cpp
@@ -163,8 +163,12 @@ void World::Render(DirectionalLighting &program) {
 	program.SetView(glm::inverse(player.Transform(player.ChunkCoords())));
 
 	for (Chunk &chunk : LoadedChunks()) {
-		program.SetM(chunk.Transform(player.ChunkCoords()));
-		chunk.Draw();
+		glm::mat4 m(chunk.Transform(player.ChunkCoords()));
+		program.SetM(m);
+		glm::mat4 mvp(program.GetVP() * m);
+		if (!CullTest(Chunk::Bounds(), mvp)) {
+			chunk.Draw();
+		}
 	}
 }
 
-- 
2.39.2