From fac4decfa4744ac6dc7f13c0348b0ec1ec80f6a4 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 21 Sep 2013 20:06:17 +0300
Subject: [PATCH] Support off-center frustum in Camera

---
 source/camera.cpp | 16 +++++++++++++++-
 source/camera.h   |  3 +++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/source/camera.cpp b/source/camera.cpp
index a3ab730d..274604f2 100644
--- a/source/camera.cpp
+++ b/source/camera.cpp
@@ -10,6 +10,8 @@ Camera::Camera():
 	aspect(4.0/3.0),
 	clip_near(0.1),
 	clip_far(10),
+	frustum_x(0),
+	frustum_y(0),
 	position(0, 0, 0),
 	look_dir(0, 0, -1),
 	up_dir(0, 1, 0)
@@ -31,6 +33,12 @@ void Camera::set_depth_clip(float n, float f)
 	clip_far = f;
 }
 
+void Camera::set_frustum_axis(float x, float y)
+{
+	frustum_x = x;
+	frustum_y = y;
+}
+
 void Camera::set_position(const Vector3 &p)
 {
 	position = p;
@@ -91,7 +99,13 @@ Vector4 Camera::unproject(const Vector4 &p) const
 
 void Camera::apply() const
 {
-	MatrixStack::projection() = Matrix::perspective(fov, aspect, clip_near, clip_far);
+	float frustum_h = tan(fov/2.0f)*clip_near;
+	float frustum_w = frustum_h*aspect;
+	float left = frustum_w*(frustum_x-1.0f);
+	float right = frustum_w*(frustum_x+1.0f);
+	float bottom = frustum_h*(frustum_y-1.0f);
+	float top = frustum_h*(frustum_y+1.0f);
+	MatrixStack::projection() = Matrix::frustum(left, right, bottom, top, clip_near, clip_far);
 	MatrixStack::modelview() = matrix;
 }
 
diff --git a/source/camera.h b/source/camera.h
index 11d42985..a0e4d6f6 100644
--- a/source/camera.h
+++ b/source/camera.h
@@ -15,6 +15,8 @@ private:
 	// Some compilers have "near" and "far" keywords
 	float clip_near;
 	float clip_far;
+	float frustum_x;
+	float frustum_y;
 	Vector3 position;
 	Vector3 look_dir;
 	Vector3 up_dir;
@@ -26,6 +28,7 @@ public:
 	void set_field_of_view(const Geometry::Angle<float> &);
 	void set_aspect(float);
 	void set_depth_clip(float, float);
+	void set_frustum_axis(float, float);
 	const Geometry::Angle<float> &get_field_of_view() const { return fov; }
 	float get_aspect() const { return aspect; }
 	float get_near_clip() const { return clip_near; }
-- 
2.43.0