From 239487e9f076c57235988fd8895e1424710d3358 Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Fri, 8 Jul 2022 17:56:44 +0200
Subject: [PATCH] Only create and load tiles within the viewport

---
 src/ol/extent.js                    | 50 ++++++++++++++++++++---------
 src/ol/renderer/canvas/TileLayer.js | 30 +++++++++++++++++
 src/ol/tilegrid/TileGrid.js         | 17 ++++++++++
 3 files changed, 82 insertions(+), 15 deletions(-)

diff --git a/src/ol/extent.js b/src/ol/extent.js
index 67d11ad039..e9ac7aa32b 100644
--- a/src/ol/extent.js
+++ b/src/ol/extent.js
@@ -531,6 +531,29 @@ export function getForViewAndSize(
   size,
   opt_extent
 ) {
+  const [x0, y0, x1, y1, x2, y2, x3, y3] = getRotatedViewport(
+    center,
+    resolution,
+    rotation,
+    size
+  );
+  return createOrUpdate(
+    Math.min(x0, x1, x2, x3),
+    Math.min(y0, y1, y2, y3),
+    Math.max(x0, x1, x2, x3),
+    Math.max(y0, y1, y2, y3),
+    opt_extent
+  );
+}
+
+/**
+ * @param {import("./coordinate.js").Coordinate} center Center.
+ * @param {number} resolution Resolution.
+ * @param {number} rotation Rotation.
+ * @param {import("./size.js").Size} size Size.
+ * @return {Array<number>} Linear ring representing the viewport.
+ */
+export function getRotatedViewport(center, resolution, rotation, size) {
   const dx = (resolution * size[0]) / 2;
   const dy = (resolution * size[1]) / 2;
   const cosRotation = Math.cos(rotation);
@@ -541,21 +564,18 @@ export function getForViewAndSize(
   const ySin = dy * sinRotation;
   const x = center[0];
   const y = center[1];
-  const x0 = x - xCos + ySin;
-  const x1 = x - xCos - ySin;
-  const x2 = x + xCos - ySin;
-  const x3 = x + xCos + ySin;
-  const y0 = y - xSin - yCos;
-  const y1 = y - xSin + yCos;
-  const y2 = y + xSin + yCos;
-  const y3 = y + xSin - yCos;
-  return createOrUpdate(
-    Math.min(x0, x1, x2, x3),
-    Math.min(y0, y1, y2, y3),
-    Math.max(x0, x1, x2, x3),
-    Math.max(y0, y1, y2, y3),
-    opt_extent
-  );
+  return [
+    x - xCos + ySin,
+    y - xSin - yCos,
+    x - xCos - ySin,
+    y - xSin + yCos,
+    x + xCos - ySin,
+    y + xSin + yCos,
+    x + xCos + ySin,
+    y + xSin - yCos,
+    x - xCos + ySin,
+    y - xSin - yCos,
+  ];
 }
 
 /**
diff --git a/src/ol/renderer/canvas/TileLayer.js b/src/ol/renderer/canvas/TileLayer.js
index 409d8b71b4..c08bd5274a 100644
--- a/src/ol/renderer/canvas/TileLayer.js
+++ b/src/ol/renderer/canvas/TileLayer.js
@@ -20,6 +20,7 @@ import {
   equals,
   getHeight,
   getIntersection,
+  getRotatedViewport,
   getTopLeft,
   getWidth,
   intersects,
@@ -308,8 +309,22 @@ class CanvasTileLayerRenderer extends CanvasLayerRenderer {
     const tmpExtent = this.tmpExtent;
     const tmpTileRange = this.tmpTileRange_;
     this.newTiles_ = false;
+    const viewport = rotation
+      ? getRotatedViewport(
+          viewState.center,
+          resolution,
+          rotation,
+          frameState.size
+        )
+      : undefined;
     for (let x = tileRange.minX; x <= tileRange.maxX; ++x) {
       for (let y = tileRange.minY; y <= tileRange.maxY; ++y) {
+        if (
+          rotation &&
+          !tileGrid.tileCoordIntersectsViewport([z, x, y], viewport)
+        ) {
+          continue;
+        }
         const tile = this.getTile(z, x, y, frameState);
         if (this.isDrawableTile(tile)) {
           const uid = getUid(this);
@@ -709,6 +724,15 @@ class CanvasTileLayerRenderer extends CanvasLayerRenderer {
     const wantedTiles = frameState.wantedTiles[tileSourceKey];
     const tileQueue = frameState.tileQueue;
     const minZoom = tileGrid.getMinZoom();
+    const rotation = frameState.viewState.rotation;
+    const viewport = rotation
+      ? getRotatedViewport(
+          frameState.viewState.center,
+          frameState.viewState.resolution,
+          rotation,
+          frameState.size
+        )
+      : undefined;
     let tileCount = 0;
     let tile, tileRange, tileResolution, x, y, z;
     for (z = minZoom; z <= currentZ; ++z) {
@@ -716,6 +740,12 @@ class CanvasTileLayerRenderer extends CanvasLayerRenderer {
       tileResolution = tileGrid.getResolution(z);
       for (x = tileRange.minX; x <= tileRange.maxX; ++x) {
         for (y = tileRange.minY; y <= tileRange.maxY; ++y) {
+          if (
+            rotation &&
+            !tileGrid.tileCoordIntersectsViewport([z, x, y], viewport)
+          ) {
+            continue;
+          }
           if (currentZ - z <= preload) {
             ++tileCount;
             tile = tileSource.getTile(z, x, y, pixelRatio, projection);
diff --git a/src/ol/tilegrid/TileGrid.js b/src/ol/tilegrid/TileGrid.js
index fb5be9a3b5..a4f6f6dde8 100644
--- a/src/ol/tilegrid/TileGrid.js
+++ b/src/ol/tilegrid/TileGrid.js
@@ -9,6 +9,7 @@ import {assert} from '../asserts.js';
 import {ceil, clamp, floor} from '../math.js';
 import {createOrUpdate, getTopLeft} from '../extent.js';
 import {createOrUpdate as createOrUpdateTileCoord} from '../tilecoord.js';
+import {intersectsLinearRing} from '../geom/flat/intersectsextent.js';
 import {isSorted, linearFindNearest} from '../array.js';
 import {toSize} from '../size.js';
 
@@ -656,6 +657,22 @@ class TileGrid {
     return clamp(z, this.minZoom, this.maxZoom);
   }
 
+  /**
+   * The tile with the provided tile coordinate intersects the given viewport.
+   * @param {import('../tilecoord.js').TileCoord} tileCoord Tile coordinate.
+   * @param {Array<number>} viewport Viewport as returned from {@link module:ol/extent.getRotatedViewport}.
+   * @return {boolean} The tile with the provided tile coordinate intersects the given viewport.
+   */
+  tileCoordIntersectsViewport(tileCoord, viewport) {
+    return intersectsLinearRing(
+      viewport,
+      0,
+      viewport.length,
+      2,
+      this.getTileCoordExtent(tileCoord)
+    );
+  }
+
   /**
    * @param {!import("../extent.js").Extent} extent Extent for this tile grid.
    * @private