From aae87475950928847a6fbbfc2664efe5204ef83b Mon Sep 17 00:00:00 2001
From: Colin Sherratt <colin.sherratt@gmail.com>
Date: Sat, 4 Oct 2014 20:09:56 -0400
Subject: [PATCH] Fix ortho projection matrix

---
 src/projection.rs   |  2 +-
 tests/projection.rs | 69 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 tests/projection.rs

diff --git a/src/projection.rs b/src/projection.rs
index 3ac3c63..2645a86 100644
--- a/src/projection.rs
+++ b/src/projection.rs
@@ -234,7 +234,7 @@ impl<S: BaseFloat> ToMatrix4<S> for Ortho<S> {
         let c2r0 = zero();
         let c2r1 = zero();
         let c2r2 = -two / (self.far - self.near);
-        let c2r3 = -one::<S>();
+        let c2r3 = zero();
 
         let c3r0 = -(self.right + self.left) / (self.right - self.left);
         let c3r1 = -(self.top + self.bottom) / (self.top - self.bottom);
diff --git a/tests/projection.rs b/tests/projection.rs
new file mode 100644
index 0000000..7e4d788
--- /dev/null
+++ b/tests/projection.rs
@@ -0,0 +1,69 @@
+// Copyright 2013-2014 The CGMath Developers. For a full listing of the authors,
+// refer to the AUTHORS file at the top-level directory of this distribution.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+extern crate cgmath;
+
+use cgmath::{Vector4, ortho, Matrix, Matrix4, Vector};
+
+#[test]
+fn test_ortho_scale() {
+    // An orthographic projection can be used to scale points
+    // but this will result in the clip space (Z) being swapped (-1 -> 1)
+    // this test asserts that this property is true of our ortho projection
+
+    let vec_near: Vector4<f32> = Vector4::new(-1., -1., -1., 1.);
+    let vec_orig: Vector4<f32> = Vector4::new(0., 0., 0., 1.);
+    let vec_far: Vector4<f32> = Vector4::new(1., 1., 1., 1.);
+
+    let o: Matrix4<f32> = ortho(-1., 1., -1., 1., -1., 1.);
+    let near = o.mul_v(&vec_near);
+    let orig = o.mul_v(&vec_orig);
+    let far = o.mul_v(&vec_far);
+
+    assert_eq!(near, Vector4::new(-1f32, -1., 1., 1.));
+    assert_eq!(orig, Vector4::new(0f32, 0., 0., 1.));
+    assert_eq!(far, Vector4::new(1f32, 1., -1., 1.));
+
+
+    let o: Matrix4<f32> = ortho(-2., 2., -2., 2., -2., 2.);
+    let near = o.mul_v(&vec_near);
+    let orig = o.mul_v(&vec_orig);
+    let far = o.mul_v(&vec_far);
+
+    assert_eq!(near, Vector4::new(-0.5f32, -0.5, 0.5, 1.));
+    assert_eq!(orig, Vector4::new(0f32, 0., 0., 1.));
+    assert_eq!(far, Vector4::new(0.5f32, 0.5, -0.5, 1.));
+}
+
+#[test]
+fn test_ortho_translate() {
+    // An orthographic projection can be used to translate a point
+    // but this will result in the clip space (Z) being swapped (-1 -> 1)
+    // this test asserts that this property is true of our ortho projection
+
+    let vec_orig: Vector4<f32> = Vector4::new(0., 0., 0., 1.);
+
+    let o: Matrix4<f32> = ortho(-1., 1., -1., 1., -1., 1.);
+    let orig = o.mul_v(&vec_orig);
+    assert_eq!(orig, Vector4::new(0., 0., 0., 1.));
+
+    let o: Matrix4<f32> = ortho(0., 2., 0., 2., 0., 2.);
+    let orig = o.mul_v(&vec_orig);
+    assert_eq!(orig, Vector4::new(-1., -1., -1., 1.));
+
+    let o: Matrix4<f32> = ortho(-2., 0., -2., 0., -2., 0.);
+    let orig = o.mul_v(&vec_orig);
+    assert_eq!(orig, Vector4::new(1., 1., 1., 1.));
+}