Add canvas type.

rtchallenge/src/canvas.rs

@@ -0,0 +1,50 @@
+use crate::tuples::{color, Color};
+
+pub struct Canvas {
+    pub height: usize,
+    pub width: usize,
+    pub pixels: Vec<Color>,
+}
+
+fn canvas(width: usize, height: usize) -> Canvas {
+    let pixels = vec![color(0., 0., 0.); width * height];
+    Canvas {
+        width,
+        height,
+        pixels,
+    }
+}
+
+impl Canvas {
+    pub fn set(&mut self, x: usize, y: usize, c: Color) {
+        self.pixels[x + y * self.width] = c;
+    }
+    pub fn get(&mut self, x: usize, y: usize) -> Color {
+        self.pixels[x + y * self.width]
+    }
+}
+#[cfg(test)]
+mod tests {
+    use super::canvas;
+
+    use crate::tuples::color;
+
+    #[test]
+    fn create_canvas() {
+        let c = canvas(10, 20);
+        assert_eq!(c.width, 10);
+        assert_eq!(c.height, 20);
+        let black = color(0., 0., 0.);
+        for (i, p) in c.pixels.iter().enumerate() {
+            assert_eq!(p, &black, "pixel {} not {:?}: {:?}", i, &black, p);
+        }
+    }
+
+    #[test]
+    fn write_to_canvas() {
+        let mut c = canvas(10, 20);
+        let red = color(1., 0., 0.);
+        c.set(2, 3, red);
+        assert_eq!(c.get(2, 3), red);
+    }
+}