step 4: add async tiles and persistent cache

AGENTS.md

@@ -2,17 +2,18 @@
 
 ## Current status
 
-Step 3 complete.
+Step 4 complete.
 
 ## Completed steps
 
 Step 1 - Public API contract and pure core.
 Step 2 - Thread-safe state, commands, overlays, and cache model.
 Step 3 - Widget shell, sizing system, and GUI-thread frame pump.
+Step 4 - Tile manager, persistent cache, and asynchronous loading.
 
 ## Current step
 
-Step 4 - Tile manager, persistent cache, and asynchronous loading.
+Step 5 - Interaction: pan, zoom, and view commands.
 
 ## Design decisions
 
@@ -45,15 +46,29 @@ None yet.
 - Implemented GUI-thread renderer frame pump that schedules frame callbacks, drains command queues, measures size, resizes the drawlist, and draws a placeholder background/attribution.
 - Implemented sizing helpers for measured size, last non-zero size preservation, visibility transitions, effective draw size, and resize dirty flags.
 - Implemented map interaction hit-rectangle calculation.
+- Implemented TileID, TileStatus, Tile, visible tile calculation, and TileManager.
+- Implemented asynchronous tile worker queue for disk reads, HTTP fetches, and image decoding.
+- Implemented provider-namespaced persistent cache writes, access metadata updates, clearing, and LRU pruning.
+- Implemented memory tile cache with visible-tile protection and deferred GUI-thread texture deletion.
+- Integrated tile result processing, stale generation/provider rejection, texture creation, and tile drawing into the GUI-thread renderer.
+- Added OpenStreetMap User-Agent warning/fallback and configured examples with example user agents.
 - Added Step 3 examples for basic map, window sizing, child-window sizing, table sizing, and hidden-tab sizing.
+- Added Step 4 cache stress example.
 - Added Step 3 tests for sizing transitions, zero-size preservation, resize dirty flags, command drain ordering, and hit rectangles.
+- Added Step 4 tests for visible tile calculation, stale result rejection, protected memory eviction, and tile image decoding.
 - Ran a Dear PyGui context smoke check for `map_widget` child-window/drawlist creation.
 - Ran `uv run pytest`.
 - Ran `uv run ruff check .`.
 - Ran `uv run ruff format .`.
 - Ran `uv run ruff format --check .`.
 - Ran `uv run pyright`.
+- Ran `uv run pytest`.
+- Ran `uv run ruff check .`.
+- Ran `uv run ruff format .`.
+- Ran `uv run ruff format --check .`.
+- Ran `uv run pyright`.
+- Ran a Dear PyGui context smoke check for `map_widget` child-window/drawlist/texture-registry creation.
 
 ## Next action
 
-Implement Step 4.
+Implement Step 5.

README.md

@@ -2,7 +2,7 @@
 
 `dpg-map` is a Dear PyGui map widget package under rebuild.
 
-The Step 3 widget shell is in place:
+The Step 4 tile manager is in place:
 
 ```python
 import dpg_map as dpgm
@@ -28,15 +28,16 @@ Implemented so far:
 - thread-safe logical map state and map registry
 - command queue with coalescing for overlay and view updates
 - logical marker, polyline, trajectory, and layer models
-- persistent disk cache path, metadata, scanning, and prune planning
+- persistent disk cache paths, metadata, scanning, pruning, and clearing
 - Dear PyGui `child_window` + measured-size `drawlist` widget shell
-- GUI-thread frame pump that drains commands and redraws a placeholder background
+- GUI-thread frame pump that drains commands, manages textures, and draws raster tiles
 - sizing helpers that preserve the last non-zero size across hidden layouts
 - interaction hit-rectangle calculation for the measured map area
+- asynchronous tile workers that read disk cache, fetch HTTP, and decode images
+- memory cache with visible-tile protection and GUI-thread texture deletion
 
-Real tile loading and overlay drawing are not implemented yet. Step 4 will add
+Overlay drawing is not implemented yet. Step 5 will add pan/zoom interaction and
-the asynchronous tile manager, persistent tile loading, and GUI-thread texture
+view command projection.
-creation.
 
 Examples:
 
@@ -46,4 +47,5 @@ uv run python examples/sizing_window.py
 uv run python examples/sizing_child.py
 uv run python examples/sizing_table.py
 uv run python examples/hidden_tab.py
+uv run python examples/cache_stress.py
 ```

examples/basic_map.py

@@ -8,6 +8,8 @@ dpg: Any = _dpg
 
 
 def main() -> None:
+    dpgm.configure(user_agent="dpg-map basic example")
+
     dpg.create_context()
     dpg.create_viewport(title="dpg-map basic", width=900, height=600)
 

examples/cache_stress.py

@@ -0,0 +1,43 @@
+from pathlib import Path
+from typing import Any
+
+import dearpygui.dearpygui as _dpg
+
+import dpg_map as dpgm
+
+dpg: Any = _dpg
+
+
+def main() -> None:
+    cache_dir = Path(__file__).resolve().parent / ".tile-cache"
+    dpgm.configure(
+        cache_dir=cache_dir,
+        memory_cache_max_tiles=32,
+        disk_cache_max_bytes=30_000_000,
+        prefetch_margin_tiles=1,
+        user_agent="dpg-map cache_stress example",
+    )
+
+    dpg.create_context()
+    dpg.create_viewport(title="dpg-map cache stress", width=1000, height=700)
+
+    with (
+        dpg.window(label="Cache Stress", width=-1, height=-1),
+        dpgm.map_widget(
+            tag="cache-map",
+            center=(47.9029, 1.9093),
+            zoom=14,
+            width=-1,
+            height=-1,
+        ),
+    ):
+        dpgm.add_marker("start", lat=47.9029, lon=1.9093, label="Orleans")
+
+    dpg.setup_dearpygui()
+    dpg.show_viewport()
+    dpg.start_dearpygui()
+    dpg.destroy_context()
+
+
+if __name__ == "__main__":
+    main()

src/dpg_map/api.py

@@ -8,7 +8,7 @@ from math import isfinite
 from pathlib import Path
 from typing import Any
 
-from .cache import CacheStats, disk_cache_size_bytes
+from .cache import CacheStats, clear_disk_cache_path, disk_cache_root, disk_cache_size_bytes
 from .commands import CommandKind, MapCommand
 from .exceptions import CoordinateError, OverlayNotFoundError
 from .overlays import LayerState, MarkerOverlay, Overlay, PolylineOverlay, TrajectoryOverlay
@@ -469,14 +469,17 @@ def set_provider(provider: str | TileProvider, *, map_tag: Tag | None = None) ->
 def clear_memory_cache(*, map_tag: Tag | None = None) -> None:
     state = get_map_state(map_tag)
     with state.lock:
+        mark_dirty(state, DirtyFlags.TILES)
         _queue(state, CommandKind.CLEAR_MEMORY_CACHE, {})
 
 
 def clear_disk_cache(*, map_tag: Tag | None = None) -> None:
     if map_tag is None:
+        clear_disk_cache_path(get_config().cache_dir)
         return
     state = get_map_state(map_tag)
     with state.lock:
+        mark_dirty(state, DirtyFlags.TILES)
         _queue(state, CommandKind.CLEAR_DISK_CACHE, {})
 
 
@@ -488,16 +491,21 @@ def get_cache_stats(*, map_tag: Tag | None = None) -> CacheStats:
             memory_max_tiles=config.memory_cache_max_tiles,
             disk_bytes=disk_cache_size_bytes(cache_dir),
             disk_max_bytes=config.disk_cache_max_bytes,
-            disk_path=cache_dir,
+            disk_path=disk_cache_root(cache_dir),
         )
     state = get_map_state(map_tag)
     with state.lock:
+        tile_snapshot = state.tile_manager.snapshot()
         return CacheStats(
-            memory_tiles=0,
+            memory_tiles=tile_snapshot.memory_tiles,
             memory_max_tiles=config.memory_cache_max_tiles,
+            memory_hits=tile_snapshot.memory_hits,
+            memory_misses=tile_snapshot.memory_misses,
             disk_bytes=disk_cache_size_bytes(state.cache_dir),
             disk_max_bytes=config.disk_cache_max_bytes,
-            disk_path=state.cache_dir,
+            disk_hits=tile_snapshot.disk_hits,
+            disk_misses=tile_snapshot.disk_misses,
+            disk_path=disk_cache_root(state.cache_dir),
         )
 
 
@@ -525,4 +533,5 @@ def get_map_debug_state(*, map_tag: Tag | None = None) -> dict[str, Any]:
             "pending_command_count": len(state.command_queue),
             "generation": state.generation,
             "active_drag": state.interaction.active_drag,
+            "tiles": asdict(state.tile_manager.snapshot()),
         }

src/dpg_map/cache.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+import shutil
 from dataclasses import asdict, dataclass, field
 from pathlib import Path
 from time import time
@@ -179,6 +180,24 @@ def write_disk_metadata(path: Path, metadata: DiskCacheMetadata) -> None:
         raise CacheError(f"could not write cache metadata: {path}") from exc
 
 
+def touch_disk_metadata(path: Path, *, accessed_at: float | None = None) -> None:
+    """Update only the last access timestamp for a metadata file."""
+
+    metadata = read_disk_metadata(path)
+    write_disk_metadata(
+        path,
+        DiskCacheMetadata(
+            url=metadata.url,
+            etag=metadata.etag,
+            last_modified=metadata.last_modified,
+            expires=metadata.expires,
+            downloaded_at=metadata.downloaded_at,
+            last_accessed_at=time() if accessed_at is None else accessed_at,
+            size_bytes=metadata.size_bytes,
+        ),
+    )
+
+
 def scan_disk_cache(cache_dir: str | Path | None) -> list[DiskCacheEntry]:
     """Scan tile files under a disk cache root."""
 
@@ -237,3 +256,34 @@ def plan_disk_prune(
         prune.append(entry.tile_path)
         total -= entry.metadata.size_bytes
     return prune
+
+
+def prune_disk_cache(
+    cache_dir: str | Path | None,
+    max_bytes: int | None,
+    *,
+    protected_paths: set[Path] | None = None,
+) -> list[Path]:
+    """Delete LRU tile files until the cache fits the configured limit."""
+
+    planned = plan_disk_prune(cache_dir, max_bytes, protected_paths=protected_paths)
+    for path in planned:
+        metadata_path = tile_metadata_path(path)
+        try:
+            path.unlink(missing_ok=True)
+            metadata_path.unlink(missing_ok=True)
+        except OSError as exc:
+            raise CacheError(f"could not prune cached tile: {path}") from exc
+    return planned
+
+
+def clear_disk_cache_path(cache_dir: str | Path | None) -> None:
+    """Remove all persistent tile cache files under a cache root."""
+
+    root = disk_cache_root(cache_dir)
+    if not root.exists():
+        return
+    try:
+        shutil.rmtree(root)
+    except OSError as exc:
+        raise CacheError(f"could not clear disk cache: {root}") from exc

src/dpg_map/renderer.py

@@ -9,16 +9,16 @@ from .commands import CommandKind, MapCommand
 from .interaction import HitRect, calculate_hit_rect
 from .sizing import SizeMeasurement, apply_size_measurement
 from .state import DirtyFlags, MapState
+from .tiles import Tile, VisibleTile
 
 
 class MapRenderer:
-    """GUI-thread renderer for the Step 3 widget shell."""
+    """GUI-thread renderer for the map widget shell and tile layer."""
 
     def __init__(self, state: MapState, dpg: Any) -> None:
         self.state = state
         self._dpg = dpg
         self._background_tag = f"{state.tag}##background"
-        self._title_tag = f"{state.tag}##placeholder-title"
         self._attribution_tag = f"{state.tag}##attribution"
         self.last_drained_commands: tuple[MapCommand, ...] = ()
         self.last_hit_rect: HitRect | None = None
@@ -43,7 +43,7 @@ class MapRenderer:
         self.schedule_next_frame()
 
     def render_frame(self) -> None:
-        """Drain pending commands, refresh size, and draw the placeholder shell."""
+        """Drain pending commands, refresh size, process tiles, and redraw."""
 
         commands = drain_renderer_commands(self.state)
         self.last_drained_commands = tuple(commands)
@@ -51,15 +51,47 @@ class MapRenderer:
 
         with self.state.lock:
             dirty = self.state.dirty
-            should_draw = bool(dirty & (DirtyFlags.FULL | DirtyFlags.SIZE))
+            should_draw = bool(dirty & (DirtyFlags.FULL | DirtyFlags.SIZE | DirtyFlags.TILES))
             visible = self.state.is_visible
             width = self.state.measured_width or self.state.last_nonzero_width
             height = self.state.measured_height or self.state.last_nonzero_height
             provider_attribution = self.state.provider.attribution
+            provider = self.state.provider
+            center = self.state.center
+            zoom = self.state.zoom
+            generation = self.state.generation
+            cache_dir = self.state.cache_dir
             self.state.dirty = DirtyFlags.NONE
 
-        if should_draw and visible:
+        accepted_tiles = self.state.tile_manager.drain_results(
-            self._draw_placeholder(width, height, provider_attribution)
+            generation=generation,
+            provider_name=provider.name,
+        )
+        self._delete_evicted_textures()
+        for tile in accepted_tiles:
+            self._ensure_texture(tile)
+
+        visible_tiles: list[VisibleTile] = []
+        if visible and width > 0 and height > 0:
+            visible_tiles = self.state.tile_manager.request_visible_tiles(
+                center=center,
+                zoom=zoom,
+                width=width,
+                height=height,
+                provider=provider,
+                generation=generation,
+                cache_dir=cache_dir,
+                margin=self._prefetch_margin(),
+            )
+
+        if visible and (should_draw or accepted_tiles):
+            self._draw_tile_layer(
+                visible_tiles=visible_tiles,
+                width=width,
+                height=height,
+                attribution=provider_attribution,
+                tile_size=provider.tile_size,
+            )
 
     def _update_size_from_dpg(self) -> None:
         width, height = self._measure_child_content()
@@ -83,7 +115,15 @@ class MapRenderer:
             return (0, 0)
         return (max(0, int(width)), max(0, int(height)))
 
-    def _draw_placeholder(self, width: int, height: int, attribution: str) -> None:
+    def _draw_tile_layer(
+        self,
+        *,
+        visible_tiles: list[VisibleTile],
+        width: int,
+        height: int,
+        attribution: str,
+        tile_size: int,
+    ) -> None:
         width = max(1, int(width))
         height = max(1, int(height))
         self._dpg.delete_item(self.state.drawlist_tag, children_only=True)
@@ -95,15 +135,19 @@ class MapRenderer:
             color=(54, 68, 78, 255),
             fill=(29, 38, 45, 255),
         )
-        self._dpg.draw_text(
+        for visible_tile in visible_tiles:
-            (12, 12),
+            tile = self.state.tile_manager.get_ready_tile(visible_tile.tile_id)
-            "dpg-map",
+            if tile is None or tile.texture_tag is None:
+                continue
+            screen_x = visible_tile.screen_x
+            screen_y = visible_tile.screen_y
+            self._dpg.draw_image(
+                tile.texture_tag,
+                (screen_x, screen_y),
+                (screen_x + tile_size, screen_y + tile_size),
                 parent=self.state.drawlist_tag,
-            tag=self._title_tag,
-            color=(232, 238, 242, 255),
-            size=18,
             )
-        label = attribution or "Map tiles load in Step 4"
+        label = attribution or "Map tiles"
         text_y = max(28, height - 24)
         self._dpg.draw_text(
             (12, text_y),
@@ -114,9 +158,36 @@ class MapRenderer:
             size=12,
         )
 
+    def _ensure_texture(self, tile: Tile) -> None:
+        if tile.texture_tag is not None:
+            return
+        texture_tag = (
+            f"{self.state.tag}##tile-{tile.tile_id.provider_name}-"
+            f"{tile.tile_id.z}-{tile.tile_id.x}-{tile.tile_id.y}"
+        )
+        if not self._dpg.does_item_exist(texture_tag):
+            self._dpg.add_static_texture(
+                tile.width,
+                tile.height,
+                tile.pixels,
+                tag=texture_tag,
+                parent=self.state.texture_registry_tag,
+            )
+        self.state.tile_manager.set_texture_tag(tile.tile_id, texture_tag)
+
+    def _delete_evicted_textures(self) -> None:
+        for texture_tag in self.state.tile_manager.take_texture_deletions():
+            if self._dpg.does_item_exist(texture_tag):
+                self._dpg.delete_item(texture_tag)
+
+    def _prefetch_margin(self) -> int:
+        from .state import get_config
+
+        return get_config().prefetch_margin_tiles
+
 
 def drain_renderer_commands(state: MapState) -> list[MapCommand]:
-    """Drain and apply GUI-thread command side effects that exist in Step 3."""
+    """Drain and apply GUI-thread command side effects."""
 
     commands = state.command_queue.drain()
     if not commands:
@@ -127,6 +198,7 @@ def drain_renderer_commands(state: MapState) -> list[MapCommand]:
             if command.kind is CommandKind.SET_VIEW:
                 state.dirty |= DirtyFlags.VIEW | DirtyFlags.TILES | DirtyFlags.OVERLAYS
             elif command.kind is CommandKind.SET_PROVIDER:
+                state.tile_manager.clear_memory_cache()
                 state.dirty |= DirtyFlags.PROVIDER | DirtyFlags.TILES
             elif command.kind in {
                 CommandKind.ADD_OVERLAY,
@@ -138,11 +210,13 @@ def drain_renderer_commands(state: MapState) -> list[MapCommand]:
             }:
                 state.dirty |= DirtyFlags.OVERLAYS
             elif command.kind is CommandKind.CLEAR_MAP:
+                state.tile_manager.clear_memory_cache()
                 state.dirty |= DirtyFlags.TILES | DirtyFlags.OVERLAYS
-            elif command.kind in {
+            elif command.kind is CommandKind.CLEAR_MEMORY_CACHE:
-                CommandKind.CLEAR_MEMORY_CACHE,
+                state.tile_manager.clear_memory_cache()
-                CommandKind.CLEAR_DISK_CACHE,
+                state.dirty |= DirtyFlags.TILES
-            }:
+            elif command.kind is CommandKind.CLEAR_DISK_CACHE:
+                state.tile_manager.clear_disk_cache(state.cache_dir)
                 state.dirty |= DirtyFlags.TILES
     return commands
 

src/dpg_map/state.py

@@ -14,6 +14,7 @@ from .commands import MapCommandQueue
 from .exceptions import InvalidProviderError, MapNotFoundError
 from .overlays import LayerState, Overlay
 from .providers import TileProvider, get_default_provider, get_provider
+from .tiles import TileManager
 from .types import LatLon, Tag
 
 
@@ -44,16 +45,6 @@ class DpgMapConfig:
     debug: bool = False
 
 
-@dataclass(slots=True)
-class TileManagerState:
-    """Logical tile/cache counters until the tile manager is implemented."""
-
-    queued_tiles: int = 0
-    loading_tiles: int = 0
-    failed_tiles: int = 0
-    visible_tile_count: int = 0
-
-
 @dataclass(slots=True)
 class InteractionState:
     """Logical interaction state until GUI interaction is implemented."""
@@ -103,7 +94,7 @@ class MapState:
     overlays: dict[Tag, Overlay] = field(default_factory=dict)
     layers: dict[str, LayerState] = field(default_factory=default_layers)
     command_queue: MapCommandQueue = field(default_factory=MapCommandQueue)
-    tile_manager: TileManagerState = field(default_factory=TileManagerState)
+    tile_manager: TileManager = field(default_factory=TileManager)
     renderer: object | None = None
     interaction: InteractionState = field(default_factory=InteractionState)
     lock: RLock = field(default_factory=RLock)
@@ -238,6 +229,12 @@ def create_map_state(
         cache_dir=resolved_cache_dir,
         user_agent=user_agent if user_agent is not None else config.user_agent,
     )
+    state.tile_manager = TileManager(
+        memory_cache_max_tiles=config.memory_cache_max_tiles,
+        disk_cache_max_bytes=config.disk_cache_max_bytes,
+        worker_count=config.tile_worker_count,
+        user_agent=state.user_agent,
+    )
     with _maps_lock:
         _maps[map_tag] = state
     return state

src/dpg_map/tiles.py

@@ -1 +1,555 @@
-"""Tile identity, lifecycle, and worker coordination."""
+"""Tile identity, lifecycle, cache, and worker coordination."""
+
+from __future__ import annotations
+
+import warnings
+from dataclasses import dataclass, field
+from enum import Enum
+from io import BytesIO
+from pathlib import Path
+from queue import Empty, Queue
+from threading import Lock, Thread
+from time import time
+from typing import Literal, cast
+
+import requests
+from PIL import Image, UnidentifiedImageError
+
+from .cache import (
+    DiskCacheMetadata,
+    MemoryCacheEntry,
+    MemoryCacheModel,
+    clear_disk_cache_path,
+    prune_disk_cache,
+    tile_cache_path,
+    tile_metadata_path,
+    touch_disk_metadata,
+    write_disk_metadata,
+)
+from .exceptions import CacheError
+from .projection import latlon_to_world, map_size
+from .providers import TileProvider
+from .types import LatLon
+
+
+class TileStatus(Enum):
+    """Lifecycle status for a tile."""
+
+    QUEUED = "queued"
+    LOADING = "loading"
+    READY = "ready"
+    FAILED = "failed"
+
+
+@dataclass(frozen=True, slots=True)
+class TileID:
+    """Provider-namespaced XYZ tile identity."""
+
+    provider_name: str
+    z: int
+    x: int
+    y: int
+
+
+@dataclass(slots=True)
+class Tile:
+    """Decoded tile data plus GUI-thread texture metadata."""
+
+    tile_id: TileID
+    status: TileStatus
+    generation: int
+    width: int = 0
+    height: int = 0
+    pixels: tuple[float, ...] = ()
+    texture_tag: object | None = None
+    source: Literal["memory", "disk", "network"] | None = None
+    error: str | None = None
+    last_accessed_at: float = field(default_factory=time)
+
+
+@dataclass(frozen=True, slots=True)
+class VisibleTile:
+    """A visible tile and its screen-space top-left point."""
+
+    tile_id: TileID
+    screen_x: float
+    screen_y: float
+
+
+@dataclass(frozen=True, slots=True)
+class TileRequest:
+    """Worker-thread tile request."""
+
+    tile_id: TileID
+    generation: int
+    url: str
+    path: Path
+    headers: dict[str, str]
+    disk_cache_max_bytes: int | None
+    protected_paths: frozenset[Path] = frozenset()
+
+
+@dataclass(frozen=True, slots=True)
+class TileResult:
+    """Worker-thread tile result consumed by the GUI thread."""
+
+    tile_id: TileID
+    generation: int
+    status: TileStatus
+    width: int = 0
+    height: int = 0
+    pixels: tuple[float, ...] = ()
+    source: Literal["disk", "network"] | None = None
+    error: str | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class TileManagerSnapshot:
+    """Thread-safe counters for diagnostics."""
+
+    queued_tiles: int
+    loading_tiles: int
+    failed_tiles: int
+    visible_tile_count: int
+    memory_tiles: int
+    memory_hits: int
+    memory_misses: int
+    disk_hits: int
+    disk_misses: int
+    stale_results: int
+
+
+def calculate_visible_tiles(
+    *,
+    center: LatLon,
+    zoom: int,
+    width: int,
+    height: int,
+    provider: TileProvider,
+    margin: int = 0,
+) -> list[VisibleTile]:
+    """Return visible XYZ tiles plus a margin, with wrapped X and clamped Y."""
+
+    if width <= 0 or height <= 0:
+        return []
+    tile_size = provider.tile_size
+    center_x, center_y = latlon_to_world(center[0], center[1], zoom, tile_size)
+    left = center_x - width / 2.0
+    top = center_y - height / 2.0
+    right = center_x + width / 2.0
+    bottom = center_y + height / 2.0
+
+    max_tile = (2**zoom) - 1
+    start_x = int(left // tile_size) - margin
+    end_x = int(right // tile_size) + margin
+    start_y = max(0, int(top // tile_size) - margin)
+    end_y = min(max_tile, int(bottom // tile_size) + margin)
+    world_size = map_size(zoom, tile_size)
+
+    tiles: list[VisibleTile] = []
+    seen: set[TileID] = set()
+    for y in range(start_y, end_y + 1):
+        for raw_x in range(start_x, end_x + 1):
+            x = raw_x % (max_tile + 1)
+            tile_id = TileID(provider.name, zoom, x, y)
+            if tile_id in seen:
+                continue
+            seen.add(tile_id)
+            tile_left = raw_x * tile_size
+            if tile_left < -tile_size:
+                tile_left += world_size
+            screen_x = tile_left - left
+            screen_y = y * tile_size - top
+            tiles.append(VisibleTile(tile_id, screen_x, screen_y))
+    return tiles
+
+
+class TileManager:
+    """Asynchronous tile loader with memory and persistent disk caches."""
+
+    def __init__(
+        self,
+        *,
+        memory_cache_max_tiles: int = 512,
+        disk_cache_max_bytes: int | None = 2_000_000_000,
+        worker_count: int = 4,
+        user_agent: str | None = None,
+    ) -> None:
+        self.memory = MemoryCacheModel(max_tiles=memory_cache_max_tiles)
+        self.disk_cache_max_bytes = disk_cache_max_bytes
+        self.worker_count = worker_count
+        self.user_agent = user_agent
+        self._tiles: dict[TileID, Tile] = {}
+        self._visible_tile_ids: set[TileID] = set()
+        self._queued: set[TileID] = set()
+        self._loading: set[TileID] = set()
+        self._failed: set[TileID] = set()
+        self._request_queue: Queue[TileRequest | None] = Queue()
+        self._result_queue: Queue[TileResult] = Queue()
+        self._threads: list[Thread] = []
+        self._lock = Lock()
+        self._delete_texture_tags: list[object] = []
+        self._disk_hits = 0
+        self._disk_misses = 0
+        self._stale_results = 0
+        self._warned_osm_user_agent = False
+
+    def start(self) -> None:
+        """Start worker threads once."""
+
+        with self._lock:
+            if self._threads:
+                return
+            count = max(1, self.worker_count)
+            for index in range(count):
+                thread = Thread(
+                    target=self._worker_loop,
+                    name=f"dpg-map-tile-worker-{index + 1}",
+                    daemon=True,
+                )
+                self._threads.append(thread)
+                thread.start()
+
+    def stop(self) -> None:
+        """Ask workers to exit."""
+
+        with self._lock:
+            threads = list(self._threads)
+            self._threads.clear()
+        for _ in threads:
+            self._request_queue.put(None)
+
+    def request_visible_tiles(
+        self,
+        *,
+        center: LatLon,
+        zoom: int,
+        width: int,
+        height: int,
+        provider: TileProvider,
+        generation: int,
+        cache_dir: str | Path | None,
+        margin: int,
+    ) -> list[VisibleTile]:
+        """Queue missing visible tiles and return their screen positions."""
+
+        visible = calculate_visible_tiles(
+            center=center,
+            zoom=zoom,
+            width=width,
+            height=height,
+            provider=provider,
+            margin=margin,
+        )
+        visible_ids = {tile.tile_id for tile in visible}
+        with self._lock:
+            self._visible_tile_ids = visible_ids
+            for entry in self.memory.entries.values():
+                entry.protected = entry.tile_id in visible_ids
+
+        self.start()
+        for visible_tile in visible:
+            self._queue_tile(
+                visible_tile.tile_id,
+                provider=provider,
+                generation=generation,
+                cache_dir=cache_dir,
+            )
+        return visible
+
+    def _queue_tile(
+        self,
+        tile_id: TileID,
+        *,
+        provider: TileProvider,
+        generation: int,
+        cache_dir: str | Path | None,
+    ) -> None:
+        with self._lock:
+            tile = self._tiles.get(tile_id)
+            if tile is not None and tile.status is TileStatus.READY:
+                self.memory.record_access(tile_id)
+                tile.last_accessed_at = time()
+                return
+            entry = self.memory.record_access(tile_id)
+            if entry is not None:
+                return
+            if tile_id in self._queued or tile_id in self._loading:
+                return
+            self._queued.add(tile_id)
+            self._tiles[tile_id] = Tile(tile_id, TileStatus.QUEUED, generation=generation)
+
+        headers = dict(provider.headers)
+        if provider.name == "osm":
+            headers = self._headers_with_osm_user_agent(headers)
+        path = tile_cache_path(
+            cache_dir,
+            provider.name,
+            tile_id.z,
+            tile_id.x,
+            tile_id.y,
+            provider.file_extension or "png",
+        )
+        request = TileRequest(
+            tile_id=tile_id,
+            generation=generation,
+            url=provider.build_url(x=tile_id.x, y=tile_id.y, z=tile_id.z),
+            path=path,
+            headers=headers,
+            disk_cache_max_bytes=self.disk_cache_max_bytes,
+            protected_paths=frozenset(path for path in self._visible_disk_paths(cache_dir)),
+        )
+        self._request_queue.put(request)
+
+    def _headers_with_osm_user_agent(self, headers: dict[str, str]) -> dict[str, str]:
+        if any(key.lower() == "user-agent" for key in headers):
+            return headers
+        if self.user_agent:
+            headers["User-Agent"] = self.user_agent
+            return headers
+        with self._lock:
+            should_warn = not self._warned_osm_user_agent
+            self._warned_osm_user_agent = True
+        if should_warn:
+            warnings.warn(
+                "OpenStreetMap tile usage should configure an application-specific user_agent",
+                RuntimeWarning,
+                stacklevel=3,
+            )
+        headers["User-Agent"] = "dpg-map/0.1"
+        return headers
+
+    def _visible_disk_paths(self, cache_dir: str | Path | None) -> list[Path]:
+        paths: list[Path] = []
+        with self._lock:
+            visible = tuple(self._visible_tile_ids)
+        for tile_id in visible:
+            paths.append(
+                tile_cache_path(
+                    cache_dir,
+                    tile_id.provider_name,
+                    tile_id.z,
+                    tile_id.x,
+                    tile_id.y,
+                )
+            )
+        return paths
+
+    def get_ready_tile(self, tile_id: TileID) -> Tile | None:
+        """Return a ready tile, updating memory LRU metadata."""
+
+        with self._lock:
+            tile = self._tiles.get(tile_id)
+            if tile is None or tile.status is not TileStatus.READY:
+                return None
+            tile.last_accessed_at = time()
+            self.memory.record_access(tile_id)
+            return tile
+
+    def drain_results(self, *, generation: int, provider_name: str) -> list[Tile]:
+        """Accept current-generation results and return ready tiles."""
+
+        accepted: list[Tile] = []
+        while True:
+            try:
+                result = self._result_queue.get_nowait()
+            except Empty:
+                break
+            with self._lock:
+                self._queued.discard(result.tile_id)
+                self._loading.discard(result.tile_id)
+                if result.generation != generation or result.tile_id.provider_name != provider_name:
+                    self._stale_results += 1
+                    continue
+                if result.status is TileStatus.FAILED:
+                    self._failed.add(result.tile_id)
+                    self._tiles[result.tile_id] = Tile(
+                        result.tile_id,
+                        TileStatus.FAILED,
+                        generation=result.generation,
+                        error=result.error,
+                    )
+                    continue
+                tile = Tile(
+                    result.tile_id,
+                    TileStatus.READY,
+                    generation=result.generation,
+                    width=result.width,
+                    height=result.height,
+                    pixels=result.pixels,
+                    source=result.source,
+                )
+                self._tiles[result.tile_id] = tile
+                self.memory.put(
+                    MemoryCacheEntry(
+                        tile_id=result.tile_id,
+                        size_bytes=len(result.pixels) * 4,
+                        protected=result.tile_id in self._visible_tile_ids,
+                        texture_tag=None,
+                    )
+                )
+                accepted.append(tile)
+            self._evict_memory_if_needed()
+        return accepted
+
+    def set_texture_tag(self, tile_id: TileID, texture_tag: object) -> None:
+        """Record a GUI-thread texture tag for a ready tile."""
+
+        with self._lock:
+            tile = self._tiles.get(tile_id)
+            if tile is not None:
+                tile.texture_tag = texture_tag
+            entry = self.memory.entries.get(tile_id)
+            if entry is not None:
+                entry.texture_tag = texture_tag
+
+    def take_texture_deletions(self) -> list[object]:
+        """Return texture tags that must be deleted by the GUI thread."""
+
+        with self._lock:
+            tags = list(self._delete_texture_tags)
+            self._delete_texture_tags.clear()
+            return tags
+
+    def clear_memory_cache(self) -> list[object]:
+        """Clear decoded memory tiles and return texture tags for GUI deletion."""
+
+        with self._lock:
+            tags = [
+                entry.texture_tag
+                for entry in self.memory.entries.values()
+                if entry.texture_tag is not None
+            ]
+            self._delete_texture_tags.extend(tags)
+            self.memory.entries.clear()
+            self._tiles.clear()
+            self._queued.clear()
+            self._loading.clear()
+            self._failed.clear()
+            return tags
+
+    def clear_disk_cache(self, cache_dir: str | Path | None) -> None:
+        """Clear the persistent cache root."""
+
+        clear_disk_cache_path(cache_dir)
+
+    def snapshot(self) -> TileManagerSnapshot:
+        """Return diagnostic counters."""
+
+        with self._lock:
+            return TileManagerSnapshot(
+                queued_tiles=len(self._queued),
+                loading_tiles=len(self._loading),
+                failed_tiles=len(self._failed),
+                visible_tile_count=len(self._visible_tile_ids),
+                memory_tiles=len(self.memory.entries),
+                memory_hits=self.memory.hits,
+                memory_misses=self.memory.misses,
+                disk_hits=self._disk_hits,
+                disk_misses=self._disk_misses,
+                stale_results=self._stale_results,
+            )
+
+    def _evict_memory_if_needed(self) -> None:
+        with self._lock:
+            evict_ids = self.memory.plan_evictions()
+            for raw_tile_id in evict_ids:
+                tile_id = cast(TileID, raw_tile_id)
+                entry = self.memory.entries.pop(tile_id, None)
+                tile = self._tiles.pop(tile_id, None)
+                texture_tag = None
+                if entry is not None:
+                    texture_tag = entry.texture_tag
+                if texture_tag is None and tile is not None:
+                    texture_tag = tile.texture_tag
+                if texture_tag is not None:
+                    self._delete_texture_tags.append(texture_tag)
+
+    def _worker_loop(self) -> None:
+        while True:
+            request = self._request_queue.get()
+            if request is None:
+                return
+            with self._lock:
+                self._queued.discard(request.tile_id)
+                self._loading.add(request.tile_id)
+                tile = self._tiles.get(request.tile_id)
+                if tile is not None:
+                    tile.status = TileStatus.LOADING
+            result = self._load_tile(request)
+            self._result_queue.put(result)
+
+    def _load_tile(self, request: TileRequest) -> TileResult:
+        try:
+            raw, source = self._read_or_fetch(request)
+            width, height, pixels = decode_tile_image(raw)
+            return TileResult(
+                request.tile_id,
+                request.generation,
+                TileStatus.READY,
+                width=width,
+                height=height,
+                pixels=pixels,
+                source=source,
+            )
+        except Exception as exc:
+            return TileResult(
+                request.tile_id,
+                request.generation,
+                TileStatus.FAILED,
+                error=str(exc),
+            )
+
+    def _read_or_fetch(self, request: TileRequest) -> tuple[bytes, Literal["disk", "network"]]:
+        if request.path.exists():
+            try:
+                raw = request.path.read_bytes()
+                touch_disk_metadata(tile_metadata_path(request.path))
+            except (OSError, CacheError):
+                raw = b""
+            if raw:
+                with self._lock:
+                    self._disk_hits += 1
+                return raw, "disk"
+
+        with self._lock:
+            self._disk_misses += 1
+        response = requests.get(request.url, headers=request.headers, timeout=20)
+        response.raise_for_status()
+        raw = response.content
+        downloaded_at = time()
+        try:
+            request.path.parent.mkdir(parents=True, exist_ok=True)
+            request.path.write_bytes(raw)
+            write_disk_metadata(
+                tile_metadata_path(request.path),
+                DiskCacheMetadata(
+                    url=request.url,
+                    etag=response.headers.get("ETag"),
+                    last_modified=response.headers.get("Last-Modified"),
+                    expires=response.headers.get("Expires"),
+                    downloaded_at=downloaded_at,
+                    last_accessed_at=downloaded_at,
+                    size_bytes=len(raw),
+                ),
+            )
+            prune_disk_cache(
+                request.path.parents[3],
+                request.disk_cache_max_bytes,
+                protected_paths=set(request.protected_paths),
+            )
+        except (OSError, CacheError):
+            pass
+        return raw, "network"
+
+
+def decode_tile_image(raw: bytes) -> tuple[int, int, tuple[float, ...]]:
+    """Decode an image into Dear PyGui-compatible RGBA float data."""
+
+    try:
+        image = Image.open(BytesIO(raw)).convert("RGBA")
+    except UnidentifiedImageError as exc:
+        raise ValueError("tile image data could not be decoded") from exc
+    width, height = image.size
+    pixels = tuple(channel / 255.0 for channel in image.tobytes())
+    return width, height, pixels

src/dpg_map/widget.py

@@ -61,6 +61,7 @@ def map_widget(
         autosize_y=autosize_y,
         **child_kwargs,
     )
+    dpg.add_texture_registry(tag=state.texture_registry_tag)
     dpg.add_drawlist(1, 1, tag=state.drawlist_tag, parent=state.child_window_tag)
 
     renderer = MapRenderer(state, dpg)

tests/test_tiles.py

@@ -0,0 +1,87 @@
+from __future__ import annotations
+
+from io import BytesIO
+
+from PIL import Image
+
+from dpg_map.providers import OSM
+from dpg_map.tiles import (
+    TileID,
+    TileManager,
+    TileResult,
+    TileStatus,
+    calculate_visible_tiles,
+    decode_tile_image,
+)
+
+
+def test_visible_tile_calculation_uses_provider_namespace() -> None:
+    tiles = calculate_visible_tiles(
+        center=(0.0, 0.0),
+        zoom=2,
+        width=256,
+        height=256,
+        provider=OSM,
+        margin=0,
+    )
+
+    assert tiles
+    assert {tile.tile_id.provider_name for tile in tiles} == {"osm"}
+    assert all(0 <= tile.tile_id.x <= 3 for tile in tiles)
+    assert all(0 <= tile.tile_id.y <= 3 for tile in tiles)
+
+
+def test_tile_manager_ignores_stale_generation_results() -> None:
+    manager = TileManager()
+    stale = TileResult(
+        TileID("osm", 1, 0, 0),
+        generation=1,
+        status=TileStatus.READY,
+        width=1,
+        height=1,
+        pixels=(1.0, 1.0, 1.0, 1.0),
+        source="disk",
+    )
+    manager._result_queue.put(stale)
+
+    accepted = manager.drain_results(generation=2, provider_name="osm")
+
+    assert accepted == []
+    assert manager.snapshot().stale_results == 1
+
+
+def test_memory_eviction_protects_visible_tiles() -> None:
+    manager = TileManager(memory_cache_max_tiles=1)
+    protected = TileID("osm", 1, 0, 0)
+    evictable = TileID("osm", 1, 0, 1)
+    with manager._lock:
+        manager._visible_tile_ids = {protected}
+
+    for tile_id in (protected, evictable):
+        manager._result_queue.put(
+            TileResult(
+                tile_id,
+                generation=1,
+                status=TileStatus.READY,
+                width=1,
+                height=1,
+                pixels=(1.0, 1.0, 1.0, 1.0),
+                source="disk",
+            )
+        )
+
+    manager.drain_results(generation=1, provider_name="osm")
+
+    assert manager.get_ready_tile(protected) is not None
+    assert manager.get_ready_tile(evictable) is None
+
+
+def test_decode_png_tile_image() -> None:
+    image = Image.new("RGBA", (1, 1), (255, 0, 128, 255))
+    buffer = BytesIO()
+    image.save(buffer, format="PNG")
+
+    width, height, pixels = decode_tile_image(buffer.getvalue())
+
+    assert (width, height) == (1, 1)
+    assert pixels == (1.0, 0.0, 128 / 255, 1.0)