feat(args.rs): adds --fall-back-to-white and --fall-back-to-black options

Author: ynn

README.md

@@ -50,6 +50,9 @@ Arguments:
 
 Options:
   -c, --codel-size <CODEL_SIZE>  Specifies the codel size (default: auto detect)
+      --fall-back-to-white       Treats unknown color as white instead of error
+      --fall-back-to-black       Treats unknown color as black instead of error
+      --max-iter <MAX_ITER>      Terminates the program after this number of iterations
   -v, --verbose                  Enables debug output (path trace etc.)
   -h, --help                     Print help
   -V, --version                  Print version
@@ -65,7 +68,9 @@ In this section, we explain how such behaviors are implemented.
 
 > *Additional colours (such as orange, brown) may be used, though their effect is implementation-dependent. In the simplest case, non-standard colours are treated by the language interpreter as the same as white, so may be used freely wherever white is used. (Another possibility is that they are treated the same as black.)*
 
-Our implementation marks any unknown color as an error, immediately terminating the interpreter before your program starts.
+By default, our implementation marks any unknown color as an error, immediately terminating the interpreter before your program starts.
+
+You can change this behavior by specifying `--fall-back-to-white` or `--fall-back-to-black` option. The former treats unknown colors as white, and the latter treats them as black.
 
 ### 3.2 Codels
 

src/args.rs

@@ -11,6 +11,14 @@ pub struct Args {
     #[arg(short, long)]
     pub codel_size: Option<usize>,
 
+    /// Treats unknown colors as white instead of error
+    #[arg(long)]
+    pub fall_back_to_white: bool,
+
+    /// Treats unknown colors as black instead of error
+    #[arg(long)]
+    pub fall_back_to_black: bool,
+
     /// Terminates the program after this number of iterations
     #[arg(long)]
     pub max_iter: Option<usize>,
@@ -19,3 +27,16 @@ pub struct Args {
     #[arg(short, long)]
     pub verbose: bool,
 }
+
+impl Args {
+    pub fn validate(&self) -> Result<(), String> {
+        if self.fall_back_to_white && self.fall_back_to_black {
+            return Err(
+                "at most one of `fall_back_to_white` and `fall_back_to_black` can be set"
+                    .to_string(),
+            );
+        }
+
+        Ok(())
+    }
+}

src/image.rs

@@ -72,7 +72,11 @@ impl Display for Image {
 }
 
 impl Image {
-    pub fn new(file: impl AsRef<Path>, codel_size: Option<usize>) -> Result<Self, Box<dyn Error>> {
+    pub fn new(
+        file: impl AsRef<Path>,
+        codel_size: Option<usize>,
+        default_color: Option<Codel>,
+    ) -> Result<Self, Box<dyn Error>> {
         let mut pixel_map = vec![];
         if !file.as_ref().exists() {
             return Err("file not found".into());
@@ -126,7 +130,9 @@ impl Image {
         for i in 0..height {
             for j in 0..width {
                 let pixel = pixel_map[i * codel_size][j * codel_size];
-                let codel = Codel::new(&pixel).ok_or(format!("invalid color at ({}, {})", i, j))?;
+                let codel = Codel::new(&pixel)
+                    .or(default_color)
+                    .ok_or(format!("invalid color at ({}, {})", i, j))?;
                 m[i].push(codel);
             }
         }

src/lib.rs

@@ -10,6 +10,7 @@ pub mod stdin;
 
 use std::error::Error;
 
+use codel::Codel;
 use rustc_hash::FxHashSet;
 
 use crate::args::Args;
@@ -27,7 +28,14 @@ fn debug_print(is_verbose_mode: bool, s: &str) {
 /// Runs a Piet program.
 //This functions is tested in integration tests.
 pub fn run(args: &Args) -> Result<(), Box<dyn Error>> {
-    let img = Image::new(&args.image_file, args.codel_size)?;
+    let default_color = if args.fall_back_to_white {
+        Some(Codel::White)
+    } else if args.fall_back_to_black {
+        Some(Codel::Black)
+    } else {
+        None
+    };
+    let img = Image::new(&args.image_file, args.codel_size, default_color)?;
     debug_print(args.verbose, &format!("{}", img));
 
     if img.get_codel_at((0, 0)).is_black() {

src/main.rs

@@ -6,5 +6,6 @@ use piet_programming_language::args::Args;
 
 fn main() -> Result<(), Box<dyn Error>> {
     let args = Args::parse();
+    args.validate()?;
     piet_programming_language::run(&args)
 }