From ca0480a8c55b38d9a5651c34b7b9b0defac22b3a Mon Sep 17 00:00:00 2001
From: Syndamia <kamen@syndamia.com>
Date: Tue, 4 Jun 2024 12:22:39 +0300
Subject: [PATCH] [hw12-hard] Implemented proper solid angle for rectangular
 lights

---
 flake.lock     | 27 +++++++++++++++++++++++++++
 flake.nix      | 26 ++++++++++++++++++++++++++
 src/lights.cpp | 32 +++++++++++++++++++-------------
 src/lights.h   |  2 ++
 src/main.cpp   |  2 +-
 src/vector.h   |  4 ++++
 6 files changed, 79 insertions(+), 14 deletions(-)
 create mode 100644 flake.lock
 create mode 100644 flake.nix

diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..25db693
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1716061101,
+        "narHash": "sha256-H0eCta7ahEgloGIwE/ihkyGstOGu+kQwAiHvwVoXaA0=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "e7cc61784ddf51c81487637b3031a6dd2d6673a2",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-23.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..d0a99fd
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,26 @@
+# Този файл, заедно с flake.lock са си за моета система, да имам копие ако случайно изтрия нещо
+{
+  description = "hexray raytracer in FMI elective";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
+  };
+
+  outputs = inputs:
+  let
+    pkgs = inputs.nixpkgs.legacyPackages."x86_64-linux";
+  in {
+    devShells."x86_64-linux".default = pkgs.mkShell {
+      nativeBuildInputs = with pkgs; [
+        cmake
+        pkg-config
+      ];
+
+      buildInputs = with pkgs; [
+        SDL2
+        openexr_3
+        zlib
+      ];
+    };
+  };
+}
diff --git a/src/lights.cpp b/src/lights.cpp
index f6edef4..d5b0ed6 100644
--- a/src/lights.cpp
+++ b/src/lights.cpp
@@ -74,9 +74,8 @@ int RectLight::intersect(const Ray& ray, double& intersectionDist)
 
 void RectLight::beginFrame()
 {
-	Vector pts[3];
-	for (int i = 0; i < 3; i++) {
-		pts[i].x = (i % 2) ? -0.5 : 0.5;
+	for (int i = 0; i < 4; i++) {
+		pts[i].x = (i % 3) ? -0.5 : 0.5;
 		pts[i].y = 0;
 		pts[i].z = (i < 2) ? -0.5 : 0.5;
 		pts[i] = T.transformPoint(pts[i]);
@@ -87,16 +86,23 @@ void RectLight::beginFrame()
 	scaleFactor = 1 / m_area;
 }
 
+static Vector projectOnUnitSphere(const Vector& toProj, const Vector& sphereCenter) {
+	return sphereCenter + normalize(toProj - sphereCenter);
+}
+
 double RectLight::getSolidAngle(const Vector& p)
 {
-	Vector lightDirCanonic(0, -1, 0);
-	//
-	Vector lightDirWorld = T.transformDir(lightDirCanonic);
-	Vector lightPosWorld = T.transformPoint(Vector(0, 0, 0));
-	Vector lightToP = p - lightPosWorld;
-	double cosTerm = dot(lightToP, lightDirWorld);
-	if (cosTerm < 0) return 0;
-	double d = lightToP.length();
-	cosTerm /= d;
-	return m_area * cosTerm / sqr(1 + d);
+	Vector ppts[4];
+	for (int i = 0; i < 4; i++) {
+		ppts[i] = projectOnUnitSphere(this->pts[i], p);
+	}
+
+	double dihedrals = 0.0;
+	for (int i = 0; i < 4; i++) {
+		Vector n1 = (ppts[(i - 1 + 4) % 4] - p) ^ (ppts[i] - p);
+		Vector n2 = (ppts[(i + 1) % 4] - p) ^ (ppts[i] - p);
+		dihedrals += radBetween(n1, n2);
+	}
+
+	return dihedrals - 2.0 * M_PI;
 }
diff --git a/src/lights.h b/src/lights.h
index c144577..e469c9d 100644
--- a/src/lights.h
+++ b/src/lights.h
@@ -100,6 +100,8 @@ class RectLight: public Light {
 	int xSubd = 3, ySubd = 3;
 	float scaleFactor;
 	double m_area;
+
+	Vector pts[4];
 public:
 	void fillProperties(ParsedBlock& pb) override
 	{
diff --git a/src/main.cpp b/src/main.cpp
index 5af773d..f0a71e5 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -379,7 +379,7 @@ bool renderStatic()
 	return render(true);
 }
 
-const char* DEFAULT_SCENE = "data/smallpt.hexray";
+const char* DEFAULT_SCENE = "data/hw12/sphtri.hexray";
 
 int main(int argc, char** argv)
 {
diff --git a/src/vector.h b/src/vector.h
index ed4c8cf..149d173 100644
--- a/src/vector.h
+++ b/src/vector.h
@@ -205,3 +205,7 @@ inline std::pair<Vector, Vector> othonormedBasis(const Vector& v)
 	result.second = result.first ^ v;
 	return result;
 }
+
+inline double radBetween(const Vector& a, const Vector& b) {
+	return acos(dot(normalize(a), normalize(b)));
+}
-- 
2.42.0