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# Auxiliary Texture Initialization
**Technical decision document for auxiliary texture initialization order**
## Problem
Auxiliary textures (inter-effect shared textures like masks) were created with incorrect dimensions, causing "half resolution" rendering bugs.
### Root Cause
```cpp
// Before fix (effect.cc:180-181)
entry.seq->init(this); // width_/height_ = 1280x720 (defaults)
entry.seq->resize(width, height); // THEN set actual dimensions (e.g., 2560x1440)
```
Effects called `register_auxiliary_texture()` during `init()` using default dimensions (1280×720) before `resize()` set actual window size. Compute shaders received uniforms with correct resolution but rendered to wrong-sized textures.
### Affected Code
- `CircleMaskEffect` - registers `"circle_mask"` texture
- `CNNEffect` - registers `"captured_frame"` texture
- `RotatingCubeEffect` - consumes `"circle_mask"` texture
- Any effect that calls `register_auxiliary_texture()` in `init()`
## Solutions Considered
### Option 1: Lazy Initialization ❌
**Approach:** Defer texture creation until first use (compute/render).
**Pros:**
- Textures created with correct dimensions
- No reallocation on resize if dimensions unchanged
- Memory saved if effect never renders
**Cons:**
- Requires `ensure_texture()` guards at every access point
- Cascade complexity: consumers (like RotatingCubeEffect) also need lazy bind group creation
- Multiple code paths, harder to debug
- Violates "initialize once" principle
**Outcome:** Attempted but rejected due to complexity cascade.
### Option 2: Reorder init/resize ✅
**Approach:** Call `resize()` before `init()` to set dimensions first.
```cpp
// After fix (effect.cc:179-180)
entry.seq->resize(width, height); // Set dimensions FIRST
entry.seq->init(this); // Then init with correct dimensions
```
**Pros:**
- **Simple:** 2-line change in MainSequence
- Dimensions available when needed during init()
- No lazy initialization complexity
- Clear, predictable initialization order
**Cons:**
- Effects see resize() before init() (unusual but harmless)
- Base `Effect::resize()` just updates width_/height_ members
**Outcome:** Implemented. Clean, maintainable solution.
## Implementation
### Changes Made
**File:** `src/gpu/effect.cc`
**Lines 179-180:**
```cpp
entry.seq->resize(width, height); // Set dimensions FIRST
entry.seq->init(this); // Then init with correct dimensions
```
**Lines 189-190:**
```cpp
seq->resize(width_, height_); // Set dimensions FIRST
seq->init(this); // Then init with correct dimensions
```
### Resize Optimization
Added early return in effects to avoid unnecessary GPU reallocation:
```cpp
void CircleMaskEffect::resize(int width, int height) {
if (width == width_ && height == height_)
return; // No-op if dimensions unchanged
Effect::resize(width, height);
if (!demo_ || !texture_initialized_)
return;
demo_->resize_auxiliary_texture("circle_mask", width, height);
// Recreate bind groups with new texture view...
}
```
## Guidelines for New Effects
### Creating Auxiliary Textures
```cpp
void MyEffect::init(MainSequence* demo) {
demo_ = demo;
// width_/height_ are VALID here (set by resize() before init())
demo_->register_auxiliary_texture("my_texture", width_, height_);
// Create pipelines and bind groups referencing the texture
}
```
### Consuming Auxiliary Textures
```cpp
void MyEffect::init(MainSequence* demo) {
demo_ = demo;
// Safe to get_auxiliary_view() here - producer effects
// initialized before consumers (order in timeline)
WGPUTextureView view = demo_->get_auxiliary_view("circle_mask");
}
```
### Handling Resize
```cpp
void MyEffect::resize(int width, int height) {
if (width == width_ && height == height_)
return; // Early exit if unchanged
Effect::resize(width, height);
// If you registered auxiliary texture, resize it:
if (demo_) {
demo_->resize_auxiliary_texture("my_texture", width, height);
// Recreate bind groups with new texture view
}
}
```
## Testing
All 36 tests pass. Verified:
- CircleMaskEffect renders at correct resolution
- CNNEffect captured_frame has correct dimensions
- No artifacts or half-resolution bugs
- Window resize works correctly
## Related Documentation
- `doc/MASKING_SYSTEM.md` - Auxiliary texture usage patterns
- `doc/EFFECT_WORKFLOW.md` - Effect creation workflow
- `src/gpu/effect.h` - MainSequence API reference
---
**Decision made:** 2026-02-11
**Implemented by:** Claude Sonnet 4.5
**Status:** Active
|
