From a8c9bac7217e1750ce7578600429d16e8010d8b1 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 16 Dec 2013 22:24:55 +0200
Subject: [PATCH] Use vector and matrix operations in ShadowMap

---
 source/shadowmap.cpp | 59 +++++++++++++++-----------------------------
 source/shadowmap.h   |  1 +
 2 files changed, 21 insertions(+), 39 deletions(-)

diff --git a/source/shadowmap.cpp b/source/shadowmap.cpp
index 86715fca..737423f7 100644
--- a/source/shadowmap.cpp
+++ b/source/shadowmap.cpp
@@ -74,58 +74,39 @@ void ShadowMap::setup_frame() const
 	renderable.setup_frame();
 	rendered = true;
 
-	Vector4 lpos = light.get_position();
-
+	const Vector4 &lpos = light.get_position();
+	Vector3 back;
 	if(lpos.w)
 	{
 		/* XXX Not really proper way to support positional lights, but good
 		enough when the light source is far away */
-		lpos -= Vector4(target.x, target.y, target.z, 1.0f);
-	}
-
-	lpos.normalize();
-
-	float matrix[16];
-	if(abs(lpos.z)>=abs(lpos.x) && abs(lpos.z)>=abs(lpos.y))
-	{
-		float d = sqrt(lpos.x*lpos.x+lpos.z*lpos.z);
-		matrix[0] = lpos.z/d;
-		matrix[4] = 0;
-		matrix[8] = -lpos.x/d;
-		matrix[1] = -lpos.x*lpos.y/d;
-		matrix[5] = d;
-		matrix[9] = -lpos.z*lpos.y/d;
+		back = Vector3(lpos)-target;
 	}
 	else
-	{
-		float d = sqrt(lpos.x*lpos.x+lpos.y*lpos.y);
-		matrix[0] = -lpos.y/d;
-		matrix[4] = lpos.x/d;
-		matrix[8] = 0;
-		matrix[1] = -lpos.x*lpos.z/d;
-		matrix[5] = -lpos.y*lpos.z/d;
-		matrix[9] = d;
-	}
+		back = Vector3(lpos);
+	back.normalize();
 
-	matrix[2] = lpos.x;
-	matrix[6] = lpos.y;
-	matrix[10] = lpos.z;
+	Vector3 up;
+	if(abs(back.z)<0.99)
+		up = Vector3(0, 0, 1);
+	else
+		up = Vector3(0, 1, 0);
 
-	matrix[12] = -(target.x*matrix[0]+target.y*matrix[4]+target.z*matrix[8]);
-	matrix[13] = -(target.x*matrix[1]+target.y*matrix[5]+target.z*matrix[9]);
-	matrix[14] = -(target.x*matrix[2]+target.y*matrix[6]+target.z*matrix[10]);
-	matrix[3] = 0;
-	matrix[7] = 0;
-	matrix[11] = 0;
-	matrix[15] = 1;
+	Vector3 right = normalize(cross(up, back));
 
-	light_matrix = matrix;
+	Vector4 columns[4];
+	columns[0] = Vector4(right, 0.0f);
+	columns[1] = Vector4(normalize(cross(back, right)), 0.0f);
+	columns[2] = Vector4(back, 0.0f);
+	columns[3] = Vector4(target, 1.0f);
+	light_matrix = Matrix::from_columns(columns);
+	view_matrix = invert(light_matrix);
 
 	MatrixStack::Push push_mv(MatrixStack::modelview());
 	MatrixStack::Push push_proj(MatrixStack::projection());
 
 	MatrixStack::projection() = Matrix::ortho(-radius, radius, -radius, radius, -radius, radius);
-	MatrixStack::modelview() = light_matrix;
+	MatrixStack::modelview() = view_matrix;
 
 	Bind bind_fbo(fbo, true);
 	Bind bind_depth(DepthTest::lequal());
@@ -144,7 +125,7 @@ void ShadowMap::render(Renderer &renderer, const Tag &tag) const
 	if(!enabled_passes.count(tag))
 		return renderer.render(renderable, tag);
 
-	const float *matrix = light_matrix.data();
+	const float *matrix = view_matrix.data();
 
 	// Has side effect of changing the current unit
 	depth_buf.bind_to(unit);
diff --git a/source/shadowmap.h b/source/shadowmap.h
index aeabaeb1..1b9d8f14 100644
--- a/source/shadowmap.h
+++ b/source/shadowmap.h
@@ -26,6 +26,7 @@ private:
 	const Light &light;
 	mutable Framebuffer fbo;
 	mutable Matrix light_matrix;
+	mutable Matrix view_matrix;
 	unsigned unit;
 	Texture2D depth_buf;
 	Vector3 target;
-- 
2.45.2