canvas: enable saving to PNG.

rtchallenge/src/canvas.rs

@@ -1,12 +1,26 @@
+use std::fs::File;
+use std::io::BufWriter;
+use std::path::Path;
+
+use png;
+use thiserror::Error;
+
 use crate::tuples::{color, Color};
 
+#[derive(Error, Debug)]
+pub enum CanvasError {
+    #[error("faile to write canvas")]
+    IOError(#[from] std::io::Error),
+    #[error("faile to encode canvas to png")]
+    EncodingError(#[from] png::EncodingError),
+}
 pub struct Canvas {
     pub height: usize,
     pub width: usize,
     pub pixels: Vec<Color>,
 }
 
-fn canvas(width: usize, height: usize) -> Canvas {
+pub fn canvas(width: usize, height: usize) -> Canvas {
     let pixels = vec![color(0., 0., 0.); width * height];
     Canvas {
         width,
@@ -17,11 +31,44 @@ fn canvas(width: usize, height: usize) -> Canvas {
 
 impl Canvas {
     pub fn set(&mut self, x: usize, y: usize, c: Color) {
+        if x > self.width {
+            return;
+        }
+        if y > self.height {
+            return;
+        }
         self.pixels[x + y * self.width] = c;
     }
     pub fn get(&mut self, x: usize, y: usize) -> Color {
         self.pixels[x + y * self.width]
     }
+    pub fn write_to_file<P>(&self, path: P) -> Result<(), CanvasError>
+    where
+        P: AsRef<Path>,
+    {
+        let path = Path::new(path.as_ref());
+        let file = File::create(path)?;
+        let ref mut w = BufWriter::new(file);
+
+        let mut encoder = png::Encoder::new(w, self.width as u32, self.height as u32);
+        encoder.set_color(png::ColorType::RGB);
+        encoder.set_depth(png::BitDepth::Eight);
+        let mut writer = encoder.write_header()?;
+
+        let data: Vec<u8> = self
+            .pixels
+            .iter()
+            .flat_map(|p| {
+                vec![
+                    (p.red.clamp(0., 1.) * 255.) as u8,
+                    (p.green.clamp(0., 1.) * 255.) as u8,
+                    (p.blue.clamp(0., 1.) * 255.) as u8,
+                ]
+            })
+            .collect();
+        writer.write_image_data(&data)?;
+        Ok(())
+    }
 }
 #[cfg(test)]
 mod tests {