Basic map view

[garado]

Basic raster tile map implementation.

• doesn't perform like absolute shit
• local map tile cache (sqlite)

[Copilot]

Pull request overview

Adds a basic raster-tile map tab to the tool UI, including tile fetching and a persistent SQLite/Room-backed tile cache.

Changes:

• Introduces TransitMapView Compose UI with pan/zoom and tile rendering.
• Adds MapTileClient to fetch Carto raster tiles with in-memory + Room disk caching and eviction.
• Wires the map tab into HomeScreen and adds Ktor/Room dependencies.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tool/src/main/kotlin/dev/garado/transit/map/TransitMapView.kt	Compose map UI: gesture handling, debounced refetch, tile drawing.
tool/src/main/kotlin/dev/garado/transit/map/MapTileClient.kt	Tile fetcher and cache orchestration (memory + Room disk cache).
tool/src/main/kotlin/dev/garado/transit/map/MapUtils.kt	Web Mercator helper utilities and projection math.
tool/src/main/kotlin/dev/garado/transit/map/TileEntity.kt	Room entity for cached tiles.
tool/src/main/kotlin/dev/garado/transit/map/TileDao.kt	Room DAO for cache read/write, touch, eviction queries.
tool/src/main/kotlin/dev/garado/transit/map/TileCacheDatabase.kt	Room database definition for tile cache.
tool/src/main/kotlin/dev/garado/transit/HomeScreen.kt	Creates the tile cache DB and replaces the placeholder Map tab with the real map view.
tool/build.gradle.kts	Adds Ktor client + Room runtime/ktx dependencies (plus KSP compiler already present).

Suppressed comments (2)

tool/src/main/kotlin/dev/garado/transit/map/TransitMapView.kt:101

• centerLat/centerLon are unbounded during pan; large values can push latitude outside Web Mercator limits, which makes lonLatToTileFraction() produce NaN/Inf and can break tile math/rendering. Clamp latitude to ±85.0511 and wrap longitude to [-180, 180) when updating the center.

                        val metersPerPx = metersPerPixel(centerLat, zoom.toDouble())
                        centerLon -= (pan.x * metersPerPx) / (METERS_PER_DEGREE_LAT * cos(Math.toRadians(centerLat)))
                        centerLat += (pan.y * metersPerPx) / METERS_PER_DEGREE_LAT
                        if (gestureZoom != 1f) {
                            zoom = (zoom + (ln(gestureZoom.toDouble()) / ln(2.0)).toFloat()).coerceIn(MIN_ZOOM, MAX_ZOOM)

tool/src/main/kotlin/dev/garado/transit/map/MapTileClient.kt:120

• fetchTilesAround launches one coroutine per tile with no concurrency limit. On larger screens this can create a burst of parallel network+DB work (and corresponding memory pressure). Consider bounding concurrent fetches (e.g., with a semaphore); keep onTileReady on the caller context to avoid mutating Compose state from a background thread.

        val tiles = tileCoords
            .map { (tileX, tileY) ->
                async {
                    fetchTile(tileX, tileY, zoom, darkMode)
                        ?.let { FetchedTile(tileX, tileY, it) }

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