From 99d97b75079debe7b7fd0aae07701651056aa2be Mon Sep 17 00:00:00 2001
From: maelstrom <maelstrom@maelstrom.dev>
Date: Fri, 10 Oct 2025 21:37:41 +0200
Subject: [PATCH] feat(rendering): added frustum class

---
 core/CMakeLists.txt            |  2 ++
 core/src/rendering/frustum.cpp | 44 ++++++++++++++++++++++++++++++++++
 core/src/rendering/frustum.h   | 29 ++++++++++++++++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 core/src/rendering/frustum.cpp
 create mode 100644 core/src/rendering/frustum.h

diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
index 7a14c9e..a3c1427 100644
--- a/core/CMakeLists.txt
+++ b/core/CMakeLists.txt
@@ -57,6 +57,8 @@ set(SOURCES
     src/rendering/font.h
     src/rendering/defaultmeshes.h
     src/rendering/texture3d.cpp
+    src/rendering/frustum.h
+    src/rendering/frustum.cpp
     src/physics/world.h
     src/physics/world.cpp
     src/logger.cpp
diff --git a/core/src/rendering/frustum.cpp b/core/src/rendering/frustum.cpp
new file mode 100644
index 0000000..526dc5f
--- /dev/null
+++ b/core/src/rendering/frustum.cpp
@@ -0,0 +1,44 @@
+#include "frustum.h"
+#include "datatypes/vector.h"
+#include <glm/ext/matrix_clip_space.hpp>
+
+// https://learnopengl.com/Guest-Articles/2021/Scene/Frustum-Culling
+
+// https://stackoverflow.com/q/66227192/16255372
+FrustumPlane::FrustumPlane(Vector3 point, Vector3 normal) : normal(normal.Unit()), distance(normal.Unit().Dot(point)) {}
+
+Frustum::Frustum(const Camera cam, float aspect, float fovY, float zNear, float zFar) {
+    const float halfVSide = zFar * tanf(fovY * 0.5f);
+    const float halfHSide = halfVSide * aspect;
+    const glm::vec3 frontMultFar = zFar * cam.cameraFront;
+
+    // Don't forget to normalize!!!
+    glm::vec3 camRight = glm::normalize(glm::cross(cam.cameraFront, -cam.cameraUp)); // Technically this is left, but whatever
+    glm::vec3 trueCamUp = glm::cross(cam.cameraFront, camRight);
+    near = { cam.cameraPos + zNear * cam.cameraFront, cam.cameraFront };
+    far = { cam.cameraPos + frontMultFar, -cam.cameraFront };
+    right = { cam.cameraPos,
+                            glm::cross(frontMultFar - camRight * halfHSide, trueCamUp) };
+    left = { cam.cameraPos,
+                            glm::cross(trueCamUp,frontMultFar + camRight * halfHSide) };
+    top = { cam.cameraPos,
+                            glm::cross(camRight, frontMultFar - trueCamUp * halfVSide) };
+    bottom = { cam.cameraPos,
+                            glm::cross(frontMultFar + trueCamUp * halfVSide, camRight) };
+}
+
+bool FrustumPlane::checkPointForward(Vector3 point) {
+    return (normal.Dot(point) - distance) < 0;
+}
+
+bool Frustum::checkPoint(Vector3 point) {
+    return true
+        // TODO: Near and far are broken for some reason
+        // && near.checkPointForward(point)
+        // && far.checkPointForward(point)
+        && left.checkPointForward(point)
+        && right.checkPointForward(point)
+        && top.checkPointForward(point)
+        && bottom.checkPointForward(point)
+        ;
+}
\ No newline at end of file
diff --git a/core/src/rendering/frustum.h b/core/src/rendering/frustum.h
new file mode 100644
index 0000000..01a4cdc
--- /dev/null
+++ b/core/src/rendering/frustum.h
@@ -0,0 +1,29 @@
+#pragma once
+
+#include "camera.h"
+#include "datatypes/vector.h"
+
+// https://learnopengl.com/Guest-Articles/2021/Scene/Frustum-Culling
+
+struct FrustumPlane {
+    Vector3 normal;
+    float distance; // leastPoint = normal * distance
+                    // leastPoint is the closest point to (0,0)
+
+    FrustumPlane(Vector3 point, Vector3 normal);
+    FrustumPlane() = default;
+
+    bool checkPointForward(Vector3);
+};
+
+struct Frustum {
+    FrustumPlane near;
+    FrustumPlane far;
+    FrustumPlane left;
+    FrustumPlane right;
+    FrustumPlane top;
+    FrustumPlane bottom;
+
+    Frustum(const Camera cam, float aspect, float fovY, float zNear, float zFar);
+    bool checkPoint(Vector3);
+};
\ No newline at end of file