From 740f2e2a0a0fcde8675e84f25e2e0a7b2ab4c0d0 Mon Sep 17 00:00:00 2001
From: James Ball <james@ball.sh>
Date: Sun, 10 Sep 2023 12:39:34 +0100
Subject: [PATCH] Slightly improve line culling

---
 Source/obj/Camera.cpp | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/Source/obj/Camera.cpp b/Source/obj/Camera.cpp
index 71c8d06..e60f824 100644
--- a/Source/obj/Camera.cpp
+++ b/Source/obj/Camera.cpp
@@ -10,9 +10,22 @@ std::vector<std::unique_ptr<Shape>> Camera::draw(WorldObject& object) {
 	for (auto edge : object.edges) {
         edge.rotate(object.rotateX, object.rotateY, object.rotateZ);
         // very crude frustum culling
-        if (edge.z1 < z || edge.z2 < z) {
+        double minZ = z + 0.1;
+        if (edge.z1 < minZ && edge.z2 < minZ) {
             continue;
         }
+        if (edge.z1 < minZ) {
+            double ratio = (minZ - edge.z1) / (edge.z2 - edge.z1);
+            edge.x1 = edge.x1 + (edge.x2 - edge.x1) * ratio;
+            edge.y1 = edge.y1 + (edge.y2 - edge.y1) * ratio;
+            edge.z1 = minZ;
+        }
+        if (edge.z2 < minZ) {
+            double ratio = (minZ - edge.z2) / (edge.z1 - edge.z2);
+            edge.x2 = edge.x2 + (edge.x1 - edge.x2) * ratio;
+            edge.y2 = edge.y2 + (edge.y1 - edge.y2) * ratio;
+            edge.z2 = minZ;
+        }
 
         Vector2 start = project(edge.x1, edge.y1, edge.z1);
         Vector2 end = project(edge.x2, edge.y2, edge.z2);