Create triangle struct (and add comments)

src/object/triangle.rs

@@ -0,0 +1,74 @@
+extern crate nalgebra as na;
+
+use na::*;
+use na::geometry::Point3;
+
+use crate::types::*;
+use super::Surface;
+
+pub struct Triangle<'a> {
+    pub vertex1: &'a Point3<f32>, // References to 3 vertices.
+    pub vertex2: &'a Point3<f32>,
+    pub vertex3: &'a Point3<f32>,
+
+    area: f32, // Precalculated area for barycentric calculations.
+
+    texture: Box<dyn Fn(f32, f32, f32) -> Color> // Texture map.
+                                                 // Uses barycentric coordinates as input.
+}
+
+pub struct TriangleMesh<'a> {
+    pub points: Vec<Box<Point3<f32>>>,
+    pub tris: Vec<Triangle<'a>>
+}
+
+fn tri_area(a: &Point3<f32>, b: &Point3<f32>, c: &Point3<f32>) -> f32 {
+    let prlg_area: f32 = (b - a).cross(&(c - a)).norm();
+    prlg_area / 2.0
+}
+
+impl<'a> Triangle<'a> {
+    pub fn new<F: 'static>(vertex1: &'a Point3<f32>,
+                            vertex2: &'a Point3<f32>,
+                            vertex3: &'a Point3<f32>,
+                            texture: F) -> Self
+        where F: Fn(f32, f32, f32) -> Color
+    {
+        Triangle {
+            vertex1: vertex1,
+            vertex2: vertex2,
+            vertex3: vertex3,
+            area: tri_area(vertex1, vertex2, vertex3),
+            texture: Box::new(texture)
+        }
+    }
+
+    pub fn new_solid(vertex1: &'a Point3<f32>,
+                    vertex2: &'a Point3<f32>,
+                    vertex3: &'a Point3<f32>, color: Color) -> Self
+        { Triangle::new(vertex1, vertex2, vertex3, move |_, _, _| color) }
+
+    // Conversion of barycentric coordinates to
+    // a point on the triangle.
+    pub fn from_bary(&self, t: f32, u: f32, v: f32) -> Point3<f32> {
+        Point::from(t * self.vertex1.coords + u * self.vertex2.coords + v * self.vertex3.coords)
+    }
+
+    // Conversion of a point to barycentric coordinates.
+    pub fn to_bary(&self, point: Point3<f32>) -> (f32, f32, f32) {
+        let t = tri_area(self.vertex2, self.vertex3, &point) / self.area;
+        let u = tri_area(self.vertex1, self.vertex3, &point) / self.area;
+        let v = tri_area(self.vertex1, self.vertex2, &point) / self.area;
+
+        (t, u, v)
+    }
+}
+
+impl<'a> TriangleMesh<'a> {
+    pub fn new(points: Vec<Box<Point3<f32>>>, tris: Vec<Triangle<'a>>) -> Self {
+        TriangleMesh {
+            points: points,
+            tris: tris
+        }
+    }
+}