From dd8300ee7cdc01d624f3a28d34e61e55fdedcc96 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Sat, 24 Oct 2026 19:31:37 +0100
Subject: [PATCH] Implement basic kernel convolution

---
 src/kernel.rs | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs    |  1 +
 2 files changed, 98 insertions(+)
 create mode 100644 src/kernel.rs

diff --git a/src/kernel.rs b/src/kernel.rs
new file mode 100644
index 0000000..642b8e6
--- /dev/null
+++ b/src/kernel.rs
@@ -0,0 +1,97 @@
+use crate::*;
+
+pub trait Kernel {
+    fn convolve(&self, img: &image::Image) -> image::Image;
+}
+
+fn sum<const N: usize>(kernel: &[[f32; N]; N]) -> f32 {
+    let mut x = 0.0;
+    for i in 0..N {
+        for j in 0..N {
+            x += kernel[j][i];
+        }
+    }
+    x
+}
+
+impl<const N: usize> Kernel for [[f32; N]; N] {
+    fn convolve(&self, img: &image::Image) -> image::Image {
+        let l = N as u32 / 2;
+		let mag = sum(self);
+
+        let extent = image::Extent {
+            x: img.extent.x - 2 * l,
+            y: img.extent.y - 2 * l,
+        };
+
+        let mut pixels = Vec::with_capacity(extent.size() as usize);
+        for y in 0..extent.y {
+			for x in 0..extent.x {
+                let mut pixel = image::Pixel::default();
+                for i in 0..N {
+                    for j in 0..N {
+                        let img_x = x as usize + i;
+                        let img_y = y as usize + j;
+                        let idx = img_y * img.extent.x as usize + img_x;
+                        pixel += img.pixels[idx] * self[j][i];
+                    }
+                }
+                pixels.push(pixel / mag);
+            }
+        }
+
+        image::Image { extent, pixels }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn size_of_result_img() {
+        let input = image::Image {
+            extent: image::Extent { x: 6, y: 10 },
+            pixels: vec![image::Pixel::default(); 60],
+        };
+        let kernel = [[1.0, 1.0, 1.0], [1.0, 1.0, 1.0], [1.0, 1.0, 1.0]];
+        let output = kernel.convolve(&input);
+        assert_eq!(output.extent.x, 4);
+        assert_eq!(output.extent.y, 8);
+    }
+
+    #[test]
+    fn single_pixel_result() {
+        let input = image::Image {
+            extent: image::Extent { x: 3, y: 3 },
+            pixels: vec![
+                image::Pixel::rgba(0.1, 0.0, 0.0, 1.0),
+                image::Pixel::rgba(0.0, 0.2, 0.0, 1.0),
+                image::Pixel::rgba(0.0, 0.0, 0.3, 1.0),
+                image::Pixel::rgba(0.2, 0.0, 0.0, 1.0),
+                image::Pixel::rgba(0.0, 0.3, 0.0, 1.0),
+                image::Pixel::rgba(0.0, 0.0, 0.1, 1.0),
+                image::Pixel::rgba(0.3, 0.0, 0.0, 1.0),
+                image::Pixel::rgba(0.0, 0.1, 0.0, 1.0),
+                image::Pixel::rgba(0.0, 0.0, 0.2, 1.0),
+            ],
+        };
+        let kernel = [[0.1, 0.2, 0.3], [0.4, 0.5, 0.6], [0.7, 0.8, 0.9]];
+        let output = kernel.convolve(&input);
+        assert_eq!(output.extent.x, 1);
+        assert_eq!(output.extent.y, 1);
+        assert_eq!(
+            output.pixels[0].r,
+            (0.1 * 0.1 + 0.2 * 0.4 + 0.3 * 0.7) / 4.5,
+        );
+        assert_eq!(
+            output.pixels[0].g,
+            (0.2 * 0.2 + 0.3 * 0.5 + 0.1 * 0.8) / 4.5,
+        );
+        assert_eq!(
+            output.pixels[0].b,
+            (0.3 * 0.3 + 0.1 * 0.6 + 0.2 * 0.9) / 4.5,
+        );
+        assert_eq!(output.pixels[0].a, 1.0);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 14995d4..2ba1056 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1,2 @@
 pub mod image;
+pub mod kernel;