CNN v2: Change feature #6 from sin(10*x) to sin(20*y)

Update positional encoding to use vertical coordinate at higher frequency.

Changes:
- train_cnn_v2.py: sin10_x → sin20_y (computed from uv_y)
- cnn_v2_static.wgsl: sin10_x → sin20_y (computed from uv_y)
- index.html: sin10_x → sin20_y (STATIC_SHADER)
- CNN_V2.md: Update feature descriptions and examples
- CNN_V2_BINARY_FORMAT.md: Update static features documentation

Feature vector: [p0, p1, p2, p3, uv_x, uv_y, sin20_y, bias]

Rationale: Higher frequency (20 vs 10) + vertical axis provides better
spatial discrimination for position encoding.

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

1 files changed, 5 insertions, 5 deletions

diff --git a/doc/CNN_V2.md b/doc/CNN_V2.md
index 2913498..78854ce 100644
--- a/doc/CNN_V2.md
+++ b/doc/CNN_V2.md
@@ -122,12 +122,12 @@ let uv_x = coord.x / resolution.x;  // Horizontal position [0,1]
 let uv_y = coord.y / resolution.y;  // Vertical position [0,1]
 
 // Slot 6: Multi-frequency position encoding
-let sin10_x = sin(10.0 * uv_x);     // Periodic feature (frequency=10)
+let sin20_y = sin(20.0 * uv_y);     // Periodic feature (frequency=20, vertical)
 
 // Slot 7: Bias dimension (always 1.0)
 let bias = 1.0;                     // Learned bias per output channel
 
-// Packed storage: [p0, p1, p2, p3, uv.x, uv.y, sin(10*uv.x), 1.0]
+// Packed storage: [p0, p1, p2, p3, uv.x, uv.y, sin(20*uv.y), 1.0]
 ```
 
 ### Feature Rationale
@@ -136,7 +136,7 @@ let bias = 1.0;                     // Learned bias per output channel
 |---------|-----------|---------|----------|
 | p0-p3 | 4D | Parametric auxiliary features (mips, gradients, etc.) | Essential |
 | UV coords | 2D | Spatial position awareness | Essential |
-| sin(10\*uv.x) | 1D | Periodic position encoding | Medium |
+| sin(20\*uv.y) | 1D | Periodic position encoding (vertical) | Medium |
 | Bias | 1D | Learned bias (standard NN) | Essential |
 
 **Note:** Input image RGBD (mip 0) fed only to Layer 0. Subsequent layers see static features + previous layer output.
@@ -149,8 +149,8 @@ let bias = 1.0;                     // Learned bias per output channel
 
 ### Future Feature Extensions
 
-**Option: Replace sin(10\*uv.x) with:**
-- `sin(20*uv.x)` - Higher frequency encoding
+**Option: Additional encodings:**
+- `sin(40*uv.y)` - Higher frequency encoding
 - `gray_mip1` - Multi-scale luminance
 - `dx`, `dy` - Sobel gradients
 - `variance` - Local texture measure