patterns: implement checker pattern.

rtchallenge/src/lib.rs

@@ -45,7 +45,7 @@ pub mod prelude {
         lights::{PointLight, PointLightBuilder},
         materials::{Material, MaterialBuilder},
         matrices::{identity, rotation_x, rotation_y, rotation_z, scaling, shearing, translation},
-        patterns::{gradient_pattern, ring_pattern, stripe_pattern},
+        patterns::{checkers_pattern, gradient_pattern, ring_pattern, stripe_pattern},
         shapes::{plane, sphere, test_shape},
         transformations::view_transform,
         tuples::{point, vector, Color},

rtchallenge/src/patterns.rs

@@ -20,6 +20,8 @@ pub enum ColorMapper {
     Gradient { a: Color, b: Color },
     /// Bullseye pattern in the XZ plane.
     Ring { a: Color, b: Color },
+    /// Traditional ray tracer tile floor pattern.
+    Checkers { a: Color, b: Color },
 }
 
 #[derive(Builder, Debug, PartialEq, Clone)]
@@ -150,6 +152,28 @@ pub fn ring_pattern(a: Color, b: Color) -> PatternBuilder {
     PatternBuilder::default().color(ColorMapper::Ring { a, b })
 }
 
+/// Builder for creating a material pattern that alternates between the given colors along the X, Y
+/// and Z pattern.  Creates traditional ray tracer tile floor pattern.
+///
+/// # Examples
+/// ```
+/// use rtchallenge::{
+///     patterns::{checkers_pattern, ColorMapper},
+///     BLACK, WHITE,
+/// };
+///
+/// # fn main() -> Result<(), Box<std::error::Error>> {
+///
+/// let pattern = checkers_pattern(BLACK, WHITE).build()?;
+/// assert_eq!(pattern.color, ColorMapper::Checkers { a: BLACK, b: WHITE });
+///
+/// # Ok(())
+/// # }
+/// ```
+pub fn checkers_pattern(a: Color, b: Color) -> PatternBuilder {
+    PatternBuilder::default().color(ColorMapper::Checkers { a, b })
+}
+
 /// Generic implementation for mapping points to colors according to the given [ColorMapper].
 impl Pattern {
     /// Create a pattern used for testing.  The color returned is the pattern space point
@@ -236,6 +260,25 @@ impl Pattern {
         }
     }
 
+    /// Create a pattern that alternates between the given colors along the X, Y and Z axis.
+    ///
+    /// # Examples
+    /// ```
+    /// use rtchallenge::{
+    ///     patterns::{ColorMapper, Pattern},
+    ///     BLACK, WHITE,
+    /// };
+    ///
+    /// let pattern = Pattern::checkers(BLACK, WHITE);
+    /// assert_eq!(pattern.color, ColorMapper::Checkers { a: BLACK, b: WHITE });
+    /// ```
+    pub fn checkers(a: Color, b: Color) -> Pattern {
+        Pattern {
+            color: ColorMapper::Checkers { a, b },
+            ..Pattern::default()
+        }
+    }
+
     /// Sample the color at the given point in untranslated object space.
     ///
     /// # Examples
@@ -292,6 +335,24 @@ impl Pattern {
     /// assert_eq!(pattern.pattern_at(point(0., 0., 1.)), BLACK);
     /// // 0.708 is slight more than 2.sqrt()/2.
     /// assert_eq!(pattern.pattern_at(point(0.708, 0., 0.708)), BLACK);
+    ///
+    /// // Checkers should repeat along X-axis.
+    /// let pattern = Pattern::checkers(WHITE, BLACK);
+    /// assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+    /// assert_eq!(pattern.pattern_at(point(0.99, 0., 0.)), WHITE);
+    /// assert_eq!(pattern.pattern_at(point(1.01, 0., 0.)), BLACK);
+    ///
+    /// // Checkers should repeat along Y-axis.
+    /// let pattern = Pattern::checkers(WHITE, BLACK);
+    /// assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+    /// assert_eq!(pattern.pattern_at(point(0., 0.99, 0.)), WHITE);
+    /// assert_eq!(pattern.pattern_at(point(0., 1.01, 0.)), BLACK);
+    ///
+    /// // Checkers should repeat along Z-axis.
+    /// let pattern = Pattern::checkers(WHITE, BLACK);
+    /// assert_eq!(pattern.pattern_at(point(0., 0., 0.)), WHITE);
+    /// assert_eq!(pattern.pattern_at(point(0., 0., 0.99)), WHITE);
+    /// assert_eq!(pattern.pattern_at(point(0., 0., 1.01)), BLACK);
     /// ```
     pub fn pattern_at(&self, point: Tuple) -> Color {
         match self.color {
@@ -319,6 +380,14 @@ impl Pattern {
                     b
                 }
             }
+            ColorMapper::Checkers { a, b } => {
+                let d = point.x.floor() + point.y.floor() + point.z.floor();
+                if d % 2. == 0. {
+                    a
+                } else {
+                    b
+                }
+            }
         }
     }
     /// Sample the color at the given world point on the given object.