feat: pixel-perfect image and gif support for G835L and proper test written

rog-anime/src/diagonal.rs

@@ -387,6 +387,11 @@ impl AnimeDiagonal {
     /// G835L diagonal packing - inverted geometry (rows grow then constant)
     /// Triangle (rows 0-27): pairs grow from 1→14 LEDs
     /// Rectangle (rows 28-67): constant 15 LEDs
+    ///
+    /// Diagonal PNG layout for G835L:
+    /// - Image height = 34 (row pairs)
+    /// - Image width  = 68 (half-step X grid)
+    /// - Even/odd rows are interleaved in X (staggered by 0.5 LED = 1 px)
     fn to_g835l_packets(&self) -> Result<AnimeDataBuffer> {
         use log::debug;
 
@@ -409,15 +414,25 @@ impl AnimeDiagonal {
             }
         }
 
+        // Helper: starting X (in LED units) for the row
+        fn first_x(row: usize) -> usize {
+            if row < 28 {
+                0
+            } else {
+                (row - 28) / 2
+            }
+        }
+
         // Process all 68 rows
         for row in 0..68 {
             let len = row_length(row);
+            let img_y = row / 2;
+            let base_x = first_x(row);
+            let stagger = row % 2;
 
             for i in 0..len {
-                // Simple horizontal reading for now - each row pair reads from same image row
-                // Row 0,1 → img row 0; Row 2,3 → img row 1; etc.
-                let img_y = row / 2;
-                let img_x = i;
+                // Half-step X grid: even rows on even pixels, odd rows on odd pixels.
+                let img_x = (base_x + i) * 2 + stagger;
 
                 // Read from image, clamp to bounds
                 let val = if img_y < self.1.len() && img_x < self.1[img_y].len() {

rog-anime/src/image.rs

@@ -141,7 +141,7 @@ impl AnimeImage {
             AnimeType::GA401 => 0.3,
             AnimeType::GU604 => 0.28,
             // TODO: Calculate correct values for G635L and G835L.
-            // Known values for G835L W*H is 34*68
+            // Known values for G835L diagonal W*H is 68*34
             AnimeType::G635L => 0.28,
             AnimeType::G835L => 0.28,
             _ => 0.283,