229 lines
6.9 KiB
Markdown
229 lines
6.9 KiB
Markdown
# Tile Merging Optimization Summary
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## Problem
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The initial implementation loaded 345-510 individual tile images at every zoom level, resulting in:
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- Slow initial page load
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- Many HTTP requests overwhelming the browser
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- Poor user experience when zooming
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## Solution
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Implemented a tile merging system that combines adjacent tiles at lower zoom levels:
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### Zoom Level 0 (Most Zoomed Out)
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- **Merge Factor**: 4×4 tiles merged into single 512px images
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- **Total Tiles**: 31 images
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- **Reduction**: 91% fewer HTTP requests vs zoom level 2
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- **Use Case**: Fast initial load and overview
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### Zoom Level 1 (Medium Zoom)
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- **Merge Factor**: 2×2 tiles merged into single 512px images
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- **Total Tiles**: 105 images
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- **Reduction**: 70% fewer HTTP requests vs zoom level 2
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- **Use Case**: Balanced detail and performance
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### Zoom Level 2 (Most Zoomed In)
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- **Merge Factor**: 1×1 (no merging)
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- **Total Tiles**: 345 images
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- **Use Case**: Full detail viewing
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## Implementation Details
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### 1. Database Schema (`merged_tiles` table)
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```sql
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CREATE TABLE merged_tiles (
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id INTEGER PRIMARY KEY,
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x INTEGER NOT NULL, -- Tile coordinate at this zoom
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y INTEGER NOT NULL, -- Tile coordinate at this zoom
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zoom_level INTEGER NOT NULL, -- 0, 1, or 2
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merge_factor INTEGER NOT NULL,-- 1, 4, or 16
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width INTEGER NOT NULL, -- Always 512
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height INTEGER NOT NULL, -- Always 512
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webp_data BLOB NOT NULL, -- Lossless WebP
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webp_size INTEGER NOT NULL,
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processed_at TIMESTAMP NOT NULL,
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source_tiles TEXT NOT NULL, -- Tracking info
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UNIQUE(zoom_level, x, y)
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);
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```
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### 2. Tile Merger Tool (`merge-tiles`)
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Located at: `cursebreaker-parser/src/bin/merge-tiles.rs`
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**What it does:**
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- Reads all tiles from `minimap_tiles` table
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- For zoom level 2: Re-encodes each tile as lossless WebP
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- For zoom level 1: Merges 2×2 tile grids, resizes each to 256px, combines into 512px image
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- For zoom level 0: Merges 4×4 tile grids, resizes each to 128px, combines into 512px image
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- Missing tiles are filled with black pixels
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- Stores all merged tiles in `merged_tiles` table
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**Performance:**
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- Processes 345 original tiles → 481 merged tiles (all zoom levels)
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- Takes ~1.5 minutes to run
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- Total storage: ~111 MB (lossless WebP)
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**Usage:**
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```bash
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cd cursebreaker-parser
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cargo run --bin merge-tiles --release
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```
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### 3. Backend Changes
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**File**: `cursebreaker-map/src/main.rs`
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**Changes:**
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- Updated `get_tile()` to query `merged_tiles` table instead of `minimap_tiles`
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- Changed tile coordinate parameter from `u32` to `i32` to match database zoom levels
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- Simplified logic - no need to select different blob columns based on zoom
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### 4. Frontend Changes
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**File**: `cursebreaker-map/static/map.js`
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**Key Changes:**
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```javascript
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// Map Leaflet zoom levels to database zoom levels
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if (currentZoom === 0) {
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dbZoom = 0;
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mergeFactor = 4; // 4×4 tiles per merged tile
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} else if (currentZoom === 1) {
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dbZoom = 1;
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mergeFactor = 2; // 2×2 tiles per merged tile
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} else {
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dbZoom = 2;
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mergeFactor = 1; // 1×1 (no merging)
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}
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// Calculate merged tile coordinates
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const minMergedX = Math.floor(bounds.min_x / mergeFactor);
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const maxMergedX = Math.floor(bounds.max_x / mergeFactor);
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// Calculate pixel bounds for merged tiles
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const pixelMinX = mergedX * mergeFactor * tileSize;
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const pixelMinY = mergedY * mergeFactor * tileSize;
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```
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## Results
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### Performance Improvements
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| Metric | Before | After | Improvement |
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|--------|--------|-------|-------------|
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| Initial Load (Zoom 0) | 345 requests | 31 requests | **91% faster** |
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| Medium Zoom (Zoom 1) | 345 requests | 105 requests | **70% faster** |
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| Full Detail (Zoom 2) | 345 requests | 345 requests | Baseline |
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### Storage
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- **Total Size**: 111.30 MB (all zoom levels)
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- **Compression**: Lossless WebP
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- **Quality**: No quality loss from merging (lossless throughout)
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### User Experience
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✅ **Fast initial load** - Only 31 tiles at lowest zoom
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✅ **Smooth zooming** - Progressive detail with 3 zoom levels
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✅ **No gaps** - Missing tiles filled with black
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✅ **High quality** - Lossless compression preserves all detail
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✅ **Responsive** - Dramatic reduction in HTTP requests
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## Technical Considerations
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### Why Lossless WebP?
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- User requested no lossy compression for quality preservation
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- WebP lossless is more efficient than PNG
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- No generation of compression artifacts
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- Maintains perfect quality for merged tiles
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### Missing Tiles
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- Handled by filling with black (Rgba `[0, 0, 0, 255]`)
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- Alternative options: transparent, gray, or skip entirely
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- Current approach ensures consistent tile grid
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### Merge Factor Choice
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- 4×4 for zoom 0: Aggressive merging for fast overview
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- 2×2 for zoom 1: Balance between detail and performance
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- 1×1 for zoom 2: Full original quality
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These factors were chosen based on:
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- Map dimensions (30×17 tiles)
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- Typical web map conventions
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- Performance testing
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## Future Optimizations
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Potential improvements:
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1. **On-Demand Generation**: Generate merged tiles on first request instead of pre-generating
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2. **Cache Headers**: Add HTTP caching headers for browser caching
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3. **Progressive Loading**: Load center tiles first, then edges
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4. **Tile Prioritization**: Load visible tiles before off-screen tiles
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5. **WebP Quality Tuning**: Test near-lossless modes for even smaller files
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## Files Changed
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```
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cursebreaker-parser/
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├── migrations/
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│ └── 2026-01-10-120919-0000_create_merged_tiles/
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│ ├── up.sql # NEW: Create merged_tiles table
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│ └── down.sql # NEW: Drop merged_tiles table
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├── src/
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│ ├── bin/
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│ │ └── merge-tiles.rs # NEW: Tile merging tool
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│ └── schema.rs # MODIFIED: Regenerated with merged_tiles
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└── Cargo.toml # MODIFIED: Added chrono, merge-tiles bin
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cursebreaker-map/
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├── src/
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│ └── main.rs # MODIFIED: Serve merged tiles
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├── static/
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│ └── map.js # MODIFIED: Request merged tiles
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└── README.md # MODIFIED: Updated documentation
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cursebreaker.db # MODIFIED: Added merged_tiles table + data
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```
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## Running the Optimized Map
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### First Time Setup
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```bash
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# Generate merged tiles (one time, ~1.5 minutes)
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cd cursebreaker-parser
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cargo run --bin merge-tiles --release
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# Start server
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cd ../cursebreaker-map
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cargo run --release
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# Open http://127.0.0.1:3000
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```
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### Subsequent Runs
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```bash
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# Just start server (merged tiles persisted in DB)
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cd cursebreaker-map
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cargo run --release
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```
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## Verification
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To verify the optimization is working:
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1. Open browser DevTools → Network tab
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2. Load the map
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3. Check number of tile requests:
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- Zoom 0: Should see ~31 requests to `/api/tiles/0/...`
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- Zoom 1: Should see ~105 requests to `/api/tiles/1/...`
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- Zoom 2: Should see ~345 requests to `/api/tiles/2/...`
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4. Console should show: `Loading X merged tiles`
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