patters: implemented basic stripe pattern.

rtchallenge/src/lib.rs

@@ -4,6 +4,7 @@ pub mod intersections;
 pub mod lights;
 pub mod materials;
 pub mod matrices;
+pub mod patterns;
 pub mod rays;
 pub mod shapes;
 pub mod transformations;

rtchallenge/src/patterns.rs

@@ -0,0 +1,67 @@
+use crate::tuples::{Color, Tuple};
+
+#[derive(Debug)]
+pub struct StripePattern {
+    pub a: Color,
+    pub b: Color,
+}
+
+/// Create a material pattern that alternates between the given colors along each unit of the
+/// X-axis.  The strip extends infinitely in the positive and negative Y and Z axes.
+///
+/// # Examples
+/// ```
+/// use rtchallenge::{patterns::stripe_pattern, BLACK, WHITE};
+///
+/// let pattern = stripe_pattern(BLACK, WHITE);
+/// assert_eq!(pattern.a, BLACK);
+/// assert_eq!(pattern.b, WHITE);
+/// ```
+pub fn stripe_pattern(a: Color, b: Color) -> StripePattern {
+    StripePattern { a, b }
+}
+
+impl StripePattern {
+    /// Sample the color at the given point.
+    ///
+    /// # Examples
+    /// ```
+    /// use rtchallenge::{patterns::stripe_pattern, tuples::point, BLACK, WHITE};
+    ///
+    /// let pattern = stripe_pattern(WHITE, BLACK);
+    ///
+    /// for (p, want) in &[
+    ///     // A stripe pattern is constant in y.
+    ///     (point(0., 0., 0.), WHITE),
+    ///     (point(0., 1., 0.), WHITE),
+    ///     (point(0., 2., 0.), WHITE),
+    ///     // A stripe pattern is constant in z.
+    ///     (point(0., 0., 0.), WHITE),
+    ///     (point(0., 0., 1.), WHITE),
+    ///     (point(0., 0., 2.), WHITE),
+    ///     // A stripe pattern alternates in z.
+    ///     (point(0., 0., 0.), WHITE),
+    ///     (point(0.9, 0., 0.), WHITE),
+    ///     (point(1., 0., 0.), BLACK),
+    ///     (point(-0.1, 0., 0.), BLACK),
+    ///     (point(-1., 0., 0.), BLACK),
+    ///     (point(-1.1, 0., 0.), WHITE),
+    /// ] {
+    ///     assert_eq!(pattern.stripe_at(*p), *want, "{:?}", p);
+    /// }
+    /// ```
+    pub fn stripe_at(&self, point: Tuple) -> Color {
+        let x = point.x.floor() as i64;
+        // Shift negative valued to get correct striping.
+        if x < 0 {
+            x - 1
+        } else {
+            x
+        };
+        if x % 2 == 0 {
+            self.a
+        } else {
+            self.b
+        }
+    }
+}