feat: allow smaller images

src/lib.rs

@@ -1,3 +1,4 @@
+#![feature(try_blocks)]
 #![warn(clippy::pedantic)]
 
 mod strandifier;

src/strandifier.rs

@@ -8,8 +8,8 @@ use crate::Layout;
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Error)]
 #[allow(clippy::module_name_repetitions)]
 pub enum StrandifierError {
-    #[error("Wrong image dimensions")]
-    WrongDimensions,
+    #[error("Image too large")]
+    ImageTooLarge,
     #[error("Invalid strand number")]
     InvalidStrand,
 }
@@ -23,6 +23,9 @@ pub struct Strandifier<'a> {
     pixels_remaining: u32,
     next_x: u32,
     next_y: u32,
+
+    offset_x: u32,
+    offset_y: u32,
 }
 
 impl<'a> Strandifier<'a> {
@@ -41,8 +44,8 @@ impl<'a> Strandifier<'a> {
         image: &'a RgbImage,
         strand_num: u32,
     ) -> Result<Self, StrandifierError> {
-        if layout.width_px() != image.width() || layout.height_px() != image.height() {
-            return Err(StrandifierError::WrongDimensions);
+        if layout.width_px() < image.width() || layout.height_px() < image.height() {
+            return Err(StrandifierError::ImageTooLarge);
         }
 
         if strand_num > layout.num_strands() {
@@ -55,6 +58,9 @@ impl<'a> Strandifier<'a> {
         let first_x = panel_x * layout.gang_len;
         let first_y = panel_y * layout.num_gangs;
 
+        let offset_x = (layout.width_px() - image.width()) / 2;
+        let offset_y = (layout.height_px() - image.height()) / 2;
+
         Ok(Self {
             layout,
             image,
@@ -62,6 +68,9 @@ impl<'a> Strandifier<'a> {
             pixels_remaining: layout.strand_len(),
             next_x: first_x,
             next_y: first_y,
+
+            offset_x,
+            offset_y,
         })
     }
 }
@@ -98,7 +107,14 @@ impl<'a> Iterator for Strandifier<'a> {
         }
         self.pixels_remaining -= 1;
 
-        Some(*self.image.get_pixel(x, y))
+        let opt_px: Option<_> = try {
+            let x = x.checked_sub(self.offset_x)?;
+            let y = y.checked_sub(self.offset_y)?;
+
+            *self.image.get_pixel_checked(x, y)?
+        };
+
+        Some(opt_px.unwrap_or(Rgb([0, 0, 0])))
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
@@ -259,12 +275,12 @@ mod tests {
         );
 
         let layout2 = Layout {
-            num_gangs: 6,
+            num_gangs: 3,
             ..layout
         };
         assert_eq!(
             Strandifier::make_strand(layout2, &image, 0).unwrap_err(),
-            StrandifierError::WrongDimensions
+            StrandifierError::ImageTooLarge
         );
     }
 }