opt: Move invariant in1 calculation outside CNN convolution loops

The in1 vector (uv_norm, gray, 1.0) is loop-invariant and doesn't depend on
dx/dy offset. Moving it outside the convolution loop eliminates redundant
computation and enables better SIMD optimization.

Updated both shader files and train.py code generation.

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

3 files changed, 11 insertions, 11 deletions

diff --git a/training/train_cnn.py b/training/train_cnn.py
index 497a07b..d8522ed 100755
--- a/training/train_cnn.py
+++ b/training/train_cnn.py
@@ -420,7 +420,8 @@ def generate_conv_src_function(kernel_size, output_path):
         # Normalize center pixel for gray channel
         f.write(f"  let original = (textureSample(tex, samp, uv) - 0.5) * 2.0;\n")
         f.write(f"  let gray = dot(original.rgb, vec3<f32>(0.2126, 0.7152, 0.0722));\n")
-        f.write(f"  let uv_norm = (uv - 0.5) * 2.0;\n\n")
+        f.write(f"  let uv_norm = (uv - 0.5) * 2.0;\n")
+        f.write(f"  let in1 = vec4<f32>(uv_norm, gray, 1.0);\n\n")
 
         f.write(f"  var sum = vec4<f32>(0.0);\n")
         f.write(f"  var pos = 0;\n\n")
@@ -429,8 +430,7 @@ def generate_conv_src_function(kernel_size, output_path):
         f.write(f"  for (var dy = -{radius}; dy <= {radius}; dy++) {{\n")
         f.write(f"    for (var dx = -{radius}; dx <= {radius}; dx++) {{\n")
         f.write(f"      let offset = vec2<f32>(f32(dx), f32(dy)) * step;\n")
-        f.write(f"      let rgbd = (textureSample(tex, samp, uv + offset) - 0.5) * 2.0;\n")
-        f.write(f"      let in1 = vec4<f32>(uv_norm, gray, 1.0);\n\n")
+        f.write(f"      let rgbd = (textureSample(tex, samp, uv + offset) - 0.5) * 2.0;\n\n")
 
         # Accumulate with dot products (unrolled)
         f.write(f"      sum.r += dot(weights[pos+0], rgbd) + dot(weights[pos+1], in1);\n")
@@ -465,7 +465,8 @@ def generate_conv_final_function(kernel_size, output_path):
         f.write(f"  weights: array<vec4<f32>, {num_positions * 2}>\n")
         f.write(f") -> f32 {{\n")
         f.write(f"  let step = 1.0 / resolution;\n")
-        f.write(f"  let uv_norm = (uv - 0.5) * 2.0;\n\n")
+        f.write(f"  let uv_norm = (uv - 0.5) * 2.0;\n")
+        f.write(f"  let in1 = vec4<f32>(uv_norm, gray, 1.0);\n\n")
         f.write(f"  var sum = 0.0;\n")
         f.write(f"  var pos = 0;\n\n")
 
@@ -473,8 +474,7 @@ def generate_conv_final_function(kernel_size, output_path):
         f.write(f"  for (var dy = -{radius}; dy <= {radius}; dy++) {{\n")
         f.write(f"    for (var dx = -{radius}; dx <= {radius}; dx++) {{\n")
         f.write(f"      let offset = vec2<f32>(f32(dx), f32(dy)) * step;\n")
-        f.write(f"      let rgbd = textureSample(tex, samp, uv + offset);\n")
-        f.write(f"      let in1 = vec4<f32>(uv_norm, gray, 1.0);\n\n")
+        f.write(f"      let rgbd = textureSample(tex, samp, uv + offset);\n\n")
 
         # Accumulate with dot products
         f.write(f"      sum += dot(weights[pos], rgbd) + dot(weights[pos+1], in1);\n")
diff --git a/workspaces/main/shaders/cnn/cnn_conv3x3.wgsl b/workspaces/main/shaders/cnn/cnn_conv3x3.wgsl
index c032767..1a5a3e1 100644
--- a/workspaces/main/shaders/cnn/cnn_conv3x3.wgsl
+++ b/workspaces/main/shaders/cnn/cnn_conv3x3.wgsl
@@ -19,6 +19,7 @@ fn cnn_conv3x3_7to4_src(
 
   // Normalize UV to [-1,1]
   let uv_norm = (uv - 0.5) * 2.0;
+  let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
   var sum = vec4<f32>(0.0);
 
@@ -27,7 +28,6 @@ fn cnn_conv3x3_7to4_src(
     for (var dx = -1; dx <= 1; dx++) {
       let offset = vec2<f32>(f32(dx), f32(dy)) * step;
       let rgbd = (textureSample(tex, samp, uv + offset) - .5) * 2.0;
-      let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
       sum.r += dot(weights[pos+0], rgbd) + dot(weights[pos+1], in1);
       sum.g += dot(weights[pos+2], rgbd) + dot(weights[pos+3], in1);
@@ -93,6 +93,7 @@ fn cnn_conv3x3_7to1(
 
   // Normalize UV to [-1,1]
   let uv_norm = (uv - 0.5) * 2.0;
+  let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
   var sum = 0.0;
 
@@ -101,7 +102,6 @@ fn cnn_conv3x3_7to1(
     for (var dx = -1; dx <= 1; dx++) {
       let offset = vec2<f32>(f32(dx), f32(dy)) * step;
       let rgbd = textureSample(tex, samp, uv + offset);
-      let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
       sum += dot(weights[pos], rgbd) + dot(weights[pos+1], in1);
       pos += 2;
diff --git a/workspaces/main/shaders/cnn/cnn_conv5x5.wgsl b/workspaces/main/shaders/cnn/cnn_conv5x5.wgsl
index 119930f..ba2a4b7 100644
--- a/workspaces/main/shaders/cnn/cnn_conv5x5.wgsl
+++ b/workspaces/main/shaders/cnn/cnn_conv5x5.wgsl
@@ -12,6 +12,7 @@ fn cnn_conv5x5_7to4(
 ) -> vec4<f32> {
   let step = 1.0 / resolution;
   let uv_norm = (uv - 0.5) * 2.0;
+  let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
   var sum = vec4<f32>(0.0);
   var pos = 0;
@@ -20,7 +21,6 @@ fn cnn_conv5x5_7to4(
     for (var dx = -2; dx <= 2; dx++) {
       let offset = vec2<f32>(f32(dx), f32(dy)) * step;
       let rgbd = textureSample(tex, samp, uv + offset);
-      let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
       sum.r += dot(weights[pos+0], rgbd) + dot(weights[pos+1], in1);
       sum.g += dot(weights[pos+2], rgbd) + dot(weights[pos+3], in1);
@@ -47,6 +47,7 @@ fn cnn_conv5x5_7to1(
 ) -> f32 {
   let step = 1.0 / resolution;
   let uv_norm = (uv - 0.5) * 2.0;
+  let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
   var sum = 0.0;
   var pos = 0;
@@ -55,7 +56,6 @@ fn cnn_conv5x5_7to1(
     for (var dx = -2; dx <= 2; dx++) {
       let offset = vec2<f32>(f32(dx), f32(dy)) * step;
       let rgbd = textureSample(tex, samp, uv + offset);
-      let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
       sum += dot(weights[pos], rgbd) + dot(weights[pos+1], in1);
       pos += 2;
@@ -79,6 +79,7 @@ fn cnn_conv5x5_7to4_src(
   let original = (textureSample(tex, samp, uv) - 0.5) * 2.0;
   let gray = dot(original.rgb, vec3<f32>(0.2126, 0.7152, 0.0722));
   let uv_norm = (uv - 0.5) * 2.0;
+  let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
   var sum = vec4<f32>(0.0);
   var pos = 0;
@@ -87,7 +88,6 @@ fn cnn_conv5x5_7to4_src(
     for (var dx = -2; dx <= 2; dx++) {
       let offset = vec2<f32>(f32(dx), f32(dy)) * step;
       let rgbd = (textureSample(tex, samp, uv + offset) - 0.5) * 2.0;
-      let in1 = vec4<f32>(uv_norm, gray, 1.0);
 
       sum.r += dot(weights[pos+0], rgbd) + dot(weights[pos+1], in1);
       sum.g += dot(weights[pos+2], rgbd) + dot(weights[pos+3], in1);