refactor: Use lazy initialization for auxiliary textures

Prevents init/resize ordering bug and avoids unnecessary reallocation.

Changes:
- Auxiliary textures created on first use (compute/update_bind_group)
- Added ensure_texture() methods to defer registration until resize()
- Added early return in resize() if dimensions unchanged
- Removed texture registration from init() methods

Benefits:
- No reallocation on window resize if dimensions match
- Texture created with correct dimensions from start
- Memory saved if effect never renders

Tests: All 36 tests passing

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

1 files changed, 13 insertions, 6 deletions

diff --git a/src/gpu/effects/cnn_effect.cc b/src/gpu/effects/cnn_effect.cc
index 84eb530..8673127 100644
--- a/src/gpu/effects/cnn_effect.cc
+++ b/src/gpu/effects/cnn_effect.cc
@@ -56,20 +56,25 @@ void CNNEffect::init(MainSequence* demo) {
   // Initialize uniforms BEFORE any bind group creation
   uniforms_.update(ctx_.queue, get_common_uniforms());
 
-  // Register captured_frame texture (used by all layers for original input)
-  if (layer_index_ == 0) {
-    demo_->register_auxiliary_texture("captured_frame", width_, height_);
-  }
-
   CNNLayerParams params = {layer_index_, blend_amount_, {0.0f, 0.0f}};
   params_buffer_.update(ctx_.queue, params);
 }
 
+void CNNEffect::ensure_texture() {
+  if (!texture_initialized_ && layer_index_ == 0 && demo_) {
+    demo_->register_auxiliary_texture("captured_frame", width_, height_);
+    texture_initialized_ = true;
+  }
+}
+
 void CNNEffect::resize(int width, int height) {
+  if (width == width_ && height == height_)
+    return;
+
   PostProcessEffect::resize(width, height);
 
   // Only layer 0 owns the captured_frame texture
-  if (layer_index_ == 0 && demo_) {
+  if (layer_index_ == 0 && demo_ && texture_initialized_) {
     demo_->resize_auxiliary_texture("captured_frame", width, height);
   }
 }
@@ -88,6 +93,8 @@ void CNNEffect::render(WGPURenderPassEncoder pass,
 }
 
 void CNNEffect::update_bind_group(WGPUTextureView input_view) {
+  ensure_texture();
+
   input_view_ = input_view;
 
   // Update common uniforms (CRITICAL for UV calculation!)