shearing

features/src/transformations.rs

@@ -48,6 +48,15 @@ impl Matrix {
             [0.0, 0.0, 0.0, 1.0],
         ])
     }
+
+    pub fn shearing(xy: f32, xz: f32, yx: f32, yz: f32, zx: f32, zy: f32) -> Self {
+        Matrix::from_array([
+            [1.0,  xy,  xz, 0.0],
+            [ yx, 1.0,  yz, 0.0],
+            [ zx,  zy, 1.0, 0.0],
+            [0.0, 0.0, 0.0, 1.0],
+        ])
+    }
 }
 
 #[cfg(test)]
@@ -157,4 +166,44 @@ mod tests {
         assert_eq!(&half_quarter * &p, Tuple::point(-1.0 * sqrt_of_2() / 2.0, sqrt_of_2() / 2.0, 0.0));
         assert_eq!(&full_quarter * &p, Tuple::point(-1.0, 0.0, 0.0));
     }
+
+    #[test]
+    fn shearing_transform_moves_x_in_proportion_to_y() {
+        let transform = Matrix::shearing(1.0, 0.0, 0.0, 0.0, 0.0, 0.0);
+        let p = Tuple::point(2.0, 3.0, 4.0);
+        
+        assert_eq!(&transform * &p, Tuple::point(5.0, 3.0, 4.0));
+    }
+
+    #[test]
+    fn shearing_transform_moves_x_in_proportion_to_z() {
+        let transform = Matrix::shearing(0.0, 1.0, 0.0, 0.0, 0.0, 0.0);
+        let p = Tuple::point(2.0, 3.0, 4.0);
+        
+        assert_eq!(&transform * &p, Tuple::point(6.0, 3.0, 4.0));
+    }
+
+    #[test]
+    fn shearing_transform_moves_y_in_proportion_to_z() {
+        let transform = Matrix::shearing(0.0, 0.0, 0.0, 1.0, 0.0, 0.0);
+        let p = Tuple::point(2.0, 3.0, 4.0);
+        
+        assert_eq!(&transform * &p, Tuple::point(2.0, 7.0, 4.0));
+    }
+
+    #[test]
+    fn shearing_transform_moves_z_in_proportion_to_x() {
+        let transform = Matrix::shearing(0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
+        let p = Tuple::point(2.0, 3.0, 4.0);
+        
+        assert_eq!(&transform * &p, Tuple::point(2.0, 3.0, 6.0));
+    }
+
+    #[test]
+    fn shearing_transform_moves_z_in_proportion_to_y() {
+        let transform = Matrix::shearing(0.0, 0.0, 0.0, 0.0, 0.0, 1.0);
+        let p = Tuple::point(2.0, 3.0, 4.0);
+        
+        assert_eq!(&transform * &p, Tuple::point(2.0, 3.0, 7.0));
+    }
 }