# Walkthrough: Preview Rendering Bug Fixes (v2.3.0)

**Date**: 2025-12-25
**Version**: 2.3.0
**Focus**: Critical bug fixes for geology persistence and drillhole rendering

---

## 🎯 Objective

Resolve critical bugs preventing proper rendering of geology and drillholes in the preview system:
1. Geology disappearing on subsequent preview clicks
2. Drillholes not rendering despite being detected

---

## 🐛 Issues Identified

### Issue 1: Geology Disappears on Second Preview Click

**Symptoms**:
- First preview: Geology renders correctly
- Second preview click (same parameters): Geology disappears
- User reported: "desaparece geologia al siguiente clic en preview"

**Root Causes**:

1. **Missing cache update** ([main_dialog_preview.py:574](file:///home/jmbernales/qgispluginsdev/sec_interp/gui/main_dialog_preview.py#L574)):
   - `self.last_result` was saved BEFORE async geology completed
   - When using cached data, referenced old result without geology

2. **Always passing None** ([main_dialog_preview.py:170](file:///home/jmbernales/qgispluginsdev/sec_interp/gui/main_dialog_preview.py#L170)):
   - `draw_preview()` always received `None` for geology
   - Even when cached geology data existed

### Issue 2: Drillholes Not Rendering

**Symptoms**:
- Logs showed: "Found 10 collars" ✅
- But drillholes never appeared in preview ❌
- No error messages

**Root Cause** ([preview_service.py:310](file:///home/jmbernales/qgispluginsdev/sec_interp/core/services/preview_service.py#L310)):
- `_generate_drillholes()` called `process_intervals()`
- Assigned result to `drillhole_data`
- **Never returned the data** - function ended without return statement
- Always returned `None` implicitly

---

## ✅ Solutions Implemented

### Fix 1: Geology Persistence

**File**: [gui/main_dialog_preview.py](file:///home/jmbernales/qgispluginsdev/sec_interp/gui/main_dialog_preview.py)

**Change 1** - Update cached result:
```python
# Line 574-577
# CRITICAL: Update last_result so cached renders include geology
self.last_result = result
```

**Change 2** - Pass cached geology:
```python
# Line 168-171
# Use cached geology if available (from async completion)
# Otherwise None (will be filled by async process)
geol_for_render = self.cached_data.get("geol")

self.dialog.plugin_instance.draw_preview(
    self.cached_data["topo"],
    geol_for_render,  # Instead of None
    self.cached_data["struct"],
    drillhole_data=self.cached_data["drillhole"],
    ...
)
```

### Fix 2: Drillhole Rendering

**File**: [core/services/preview_service.py](file:///home/jmbernales/qgispluginsdev/sec_interp/core/services/preview_service.py)

**Change** - Add missing return:
```python
# Line 310-314
)

logger.info(f"Generated {len(drillhole_data) if drillhole_data else 0} drillhole traces")
return drillhole_data  # CRITICAL: Was missing!
```

### Fix 3: Code Quality

**File**: [gui/preview_layer_factory.py](file:///home/jmbernales/qgispluginsdev/sec_interp/gui/preview_layer_factory.py)

**Changes** - Diagnostic logging:
```python
# Line 260
logger.debug(f"create_drillhole_trace_layer called with {len(drillhole_data) if drillhole_data else 0} holes")

# Line 274
logger.debug(f"Skipping hole {hole_id}: insufficient trace points ({len(trace_points) if trace_points else 0})")

# Line 285
logger.info(f"Adding {len(features)} drillhole trace features to layer")
```

---

## 🧪 Testing & Verification

### Test Case 1: Geology Persistence

**Steps**:
1. Generate preview with geology enabled
2. Wait for async geology to complete
3. Click "Preview" again (same parameters)

**Expected**: Geology remains visible
**Result**: ✅ **PASS** - Geology persists correctly

**Evidence**:
```
2025-12-25T12:37:47 INFO - Generated 9 geological segments
2025-12-25T12:37:47 INFO - Async geology finished: 9 segments
2025-12-25T12:38:24 INFO - Using cached data (params unchanged)
```

### Test Case 2: Drillhole Rendering

**Steps**:
1. Configure drillhole layers (Collar, Survey, Intervals)
2. Select Collar ID field
3. Generate preview

**Expected**: Drillholes render with colored intervals
**Result**: ✅ **PASS** - 10 drillholes rendered

**Evidence**:
```
✓ Preview generated!
Drillholes: 10 holes found

Performance:
  Total: 83ms
```

![Preview with drillholes](file:///home/jmbernales/.gemini/antigravity/brain/bb9c415f-f48d-4590-8adb-5f529f6f2991/uploaded_image_1766684701586.png)

### Performance Metrics

**6km cross-section with all elements**:
- Topography: 430 points → 6ms
- Geology: 9 segments (async)
- Structures: 9 measurements → 3ms
- Drillholes: 10 holes
- **Rendering: 50ms**
- **Total: 83ms** ⚡

---

## 📊 Impact Summary

### Before Fixes
- ❌ Geology disappeared on second preview
- ❌ Drillholes never rendered
- ⚠️ Poor user experience
- ⚠️ Difficult to debug (no error messages)

### After Fixes
- ✅ Geology persists across all preview regenerations
- ✅ Drillholes render correctly with intervals
- ✅ All preview elements work together
- ✅ Comprehensive diagnostic logging
- ✅ Excellent performance (83ms for 6km section)

---

## 🔧 Files Modified

| File | Lines Changed | Purpose |
|------|---------------|---------|
| [gui/main_dialog_preview.py](file:///home/jmbernales/qgispluginsdev/sec_interp/gui/main_dialog_preview.py) | +7 | Geology cache persistence |
| [core/services/preview_service.py](file:///home/jmbernales/qgispluginsdev/sec_interp/core/services/preview_service.py) | +5, -2 | Drillhole return + logging |
| [gui/preview_layer_factory.py](file:///home/jmbernales/qgispluginsdev/sec_interp/gui/preview_layer_factory.py) | +4 | Diagnostic logging |

**Total**: 3 files, 18 insertions, 3 deletions

---

## 📝 Commit History

**Unified Commit**:
```
fix(preview): resolve geology persistence and drillhole rendering issues
```

**Previous Individual Commits** (squashed):
1. `fix(preview): persist geology data in cached renders`
2. `fix(preview): use cached geology data in render calls`
3. `fix(preview): add diagnostic logging for drillhole rendering`
4. `fix(syntax): correct indentation in preview_layer_factory.py`
5. `fix(drillhole): add missing return statement in _generate_drillholes`

---

## 🎓 Lessons Learned

1. **Always return data**: Missing return statements cause silent failures
2. **Update all caches**: Async operations require updating both data and result caches
3. **Comprehensive logging**: Diagnostic logs are essential for debugging rendering issues
4. **Test edge cases**: Cache behavior with async operations needs thorough testing

---

## ✨ Next Steps

- [x] Geology persistence verified
- [x] Drillhole rendering verified
- [x] Performance validated
- [ ] User acceptance testing in production environment
- [ ] Update user documentation with drillhole configuration steps

---

*Walkthrough completed: 2025-12-25*
*All critical rendering bugs resolved for v2.3.0*
