Parsing more stuff.

ray-tracing-core/src/affine_transform.rs

@@ -9,6 +9,11 @@ pub struct AffineTransform {
 }
 
 impl AffineTransform {
+    pub fn new(mat: [[Float; 4]; 3]) -> Option<Self> {
+        let inv = Self::invert(mat)?;
+        Some(Self { mat, inv })
+    }
+
     pub fn identity() -> Self {
         Self {
             mat: [
@@ -77,7 +82,7 @@ impl AffineTransform {
         }
     }
 
-    pub fn look_at(pos: Pos3, look: Pos3, up: Dir3) -> Self {
+    pub fn look_at(pos: Pos3, look: Pos3, up: Dir3) -> Option<Self> {
         let dir = (look - pos).normalize();
         let right = Dir3::cross(up.normalize(), dir).normalize();
         let new_up = Dir3::cross(dir, right);
@@ -88,14 +93,55 @@ impl AffineTransform {
             [right.z(), new_up.z(), dir.z(), pos.z()],
         ];
 
-        let inv = Self::invert(mat);
-
-        Self { mat, inv }
+        Self::new(mat)
     }
 
-    fn invert(mat: [[Float; 4]; 3]) -> [[Float; 3]; 3] {
-        eprintln!("Matrix inversion not implemented");
-        [[0.0; 3]; 3]
+    fn invert(mat: [[Float; 4]; 3]) -> Option<[[Float; 3]; 3]> {
+        // using cramers rule
+        let adj = |y, x| {
+            let cofactor_indices = |p| match p {
+                0 => (1, 2),
+                1 => (0, 2),
+                2 => (0, 1),
+                _ => unreachable!(),
+            };
+            let (y1, y2) = cofactor_indices(y);
+            let (x1, x2) = cofactor_indices(x);
+
+            (if (x + y) % 2 == 0 { 1.0 } else { -1.0 })
+                * (mat[y1][x1] * mat[y2][x2] - mat[y1][x2] * mat[y2][x1])
+        };
+
+        let det = mat[0][0] * mat[1][1] * mat[2][2]
+            + mat[0][1] * mat[1][2] * mat[2][0]
+            + mat[0][2] * mat[1][0] * mat[2][1]
+            - mat[0][2] * mat[1][1] * mat[2][0]
+            - mat[0][1] * mat[1][0] * mat[2][2]
+            - mat[0][0] * mat[1][2] * mat[2][1];
+
+        if det != 0.0 {
+            let det_frac = 1.0 / det;
+
+            Some([
+                [
+                    adj(0, 0) * det_frac,
+                    adj(1, 0) * det_frac,
+                    adj(2, 0) * det_frac,
+                ],
+                [
+                    adj(0, 1) * det_frac,
+                    adj(1, 1) * det_frac,
+                    adj(2, 1) * det_frac,
+                ],
+                [
+                    adj(0, 2) * det_frac,
+                    adj(1, 2) * det_frac,
+                    adj(2, 2) * det_frac,
+                ],
+            ])
+        } else {
+            None
+        }
     }
 
     pub fn transform_pos(&self, pos: Pos3) -> Pos3 {