From 378ec6bf157f821dbc3f3eba395e7616251ddb0b Mon Sep 17 00:00:00 2001
From: ache <ache@ache.one>
Date: Sun, 27 Apr 2025 00:22:53 +0200
Subject: Implement serpentine scanning

---
 src/lib.rs | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)

(limited to 'src')

diff --git a/src/lib.rs b/src/lib.rs
index a479934..4bc5ab4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -444,6 +444,86 @@ pub fn dither(image: &mut RgbImage, kernel: kernel::Kernel) {
         *pixel_ = image::Rgb([pixel, pixel, pixel]);
     }
 }
+pub fn dither_serpentine_1b(image: &mut RgbImage, kernel: kernel::Kernel) {
+    let (width, height) = image.dimensions();
+    let (width, height): (usize, usize) = (width as usize, height as usize);
+    let error_buffer_size = kernel
+        .iter()
+        .map(|k| k.dx + k.dy * width as i32)
+        .max()
+        .unwrap() as usize;
+    assert!(error_buffer_size > 0);
+    let mut error: Vec<f32> = vec![0.; error_buffer_size];
+
+    for y in 0..(height as u32) {
+        let serpentine_coef: i32 = if y % 2 == 0 { 1 } else { 1 };
+        for x in 0..(width as u32) {
+            let x = if y % 2 == 0 { x } else { width as u32 - 1 - x };
+
+            let Rgb([r, g, b]) = image.get_pixel(x, y);
+            let pixel = (*r as f32 + *g as f32 + *b as f32) as f32 / 3.;
+            let err_pos: u32 = (y * width as u32 + x) % (error_buffer_size as u32);
+
+            // let (pixel, err) = dither_float_chose_color(error[err_pos as usize], pixel);
+            let (pixel, err) = dither_atkinson_chose_color(error[err_pos as usize], pixel);
+
+            for e in &kernel {
+                error[(err_pos as i32 + e.dx * serpentine_coef + width as i32 * e.dy)
+                    .rem_euclid(error_buffer_size as i32) as usize] += err * e.weight;
+            }
+            error[err_pos as usize] = 0.;
+
+            image.put_pixel(x, y, image::Rgb([pixel, pixel, pixel]));
+        }
+    }
+}
+pub fn dither_serpentine_3b(image: &mut RgbImage, kernel: kernel::Kernel) {
+    let (width, height) = image.dimensions();
+    let (width, height): (usize, usize) = (width as usize, height as usize);
+    let error_buffer_size = kernel
+        .iter()
+        .map(|k| k.dx + k.dy * width as i32)
+        .max()
+        .unwrap() as usize;
+    assert!(error_buffer_size > 0);
+    let mut error: [Vec<f32>; 3] = [
+        vec![0.; error_buffer_size],
+        vec![0.; error_buffer_size],
+        vec![0.; error_buffer_size],
+    ];
+
+    for y in 0..(height as u32) {
+        let serpentine_coef: i32 = if y % 2 == 0 { 1 } else { 1 };
+        for x in 0..(width as u32) {
+            let x = if y % 2 == 0 { x } else { width as u32 - 1 - x };
+
+            let pixel = image.get_pixel(x, y);
+            let err_pos: u32 = (y * width as u32 + x) % (error_buffer_size as u32);
+
+            // let (pixel, err) = dither_float_chose_color(error[err_pos as usize], pixel);
+            let (new_pixel, err) = dither_float_chose_3b(
+                error[0][err_pos as usize],
+                error[1][err_pos as usize],
+                error[2][err_pos as usize],
+                *pixel,
+            );
+
+            for i in 0..3 {
+                error[i][err_pos as usize] = 0.;
+            }
+
+            for e in &kernel {
+                for i in 0..3 {
+                    error[i][(err_pos as i32 + e.dx * serpentine_coef + width as i32 * e.dy)
+                        .rem_euclid(error_buffer_size as i32)
+                        as usize] += err[i] * e.weight;
+                }
+            }
+
+            image.put_pixel(x, y, new_pixel);
+        }
+    }
+}
 pub fn dither_float(image: &mut RgbImage, kernel: kernel::Kernel) {
     let (width, _height) = image.dimensions();
     let width = width as usize;
-- 
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