fix: Correct UV coordinate computation to match PyTorch linspace

Critical mismatch: shader used pixel-center coordinates while PyTorch
uses pixel-corner coordinates, causing 0.5-pixel offset.

PyTorch: linspace(0, 1, H) → [0, 1/(H-1), ..., 1]
Shader: (p.xy - 0.5) / (resolution - 1.0) to match

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/workspaces/main/shaders/cnn/cnn_layer.wgsl b/workspaces/main/shaders/cnn/cnn_layer.wgsl
index 8eccb26..d33a301 100644
--- a/workspaces/main/shaders/cnn/cnn_layer.wgsl
+++ b/workspaces/main/shaders/cnn/cnn_layer.wgsl
@@ -29,7 +29,8 @@ struct CNNLayerParams {
 }
 
 @fragment fn fs_main(@builtin(position) p: vec4<f32>) -> @location(0) vec4<f32> {
-    let uv = p.xy / uniforms.resolution;
+    // Match PyTorch linspace: pixel_idx / (size - 1), not pixel_center / size
+    let uv = (p.xy - 0.5) / (uniforms.resolution - 1.0);
     let original_raw = textureSample(original_input, smplr, uv);
     let original = (original_raw - 0.5) * 2.0;  // Normalize to [-1,1]
     let gray = dot(original.rgb, vec3<f32>(0.2126, 0.7152, 0.0722));