From b7d022f80e952ab75cac4ed5bddd0231d628aebd Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Thu, 17 Feb 2022 18:12:19 +0100
Subject: [PATCH] Use same clipping method for vector and image tiles

---
 src/ol/renderer/canvas/VectorTileLayer.js | 56 +++++++++++++++++++++--
 1 file changed, 51 insertions(+), 5 deletions(-)

diff --git a/src/ol/renderer/canvas/VectorTileLayer.js b/src/ol/renderer/canvas/VectorTileLayer.js
index 1862ee8a9c..724404df98 100644
--- a/src/ol/renderer/canvas/VectorTileLayer.js
+++ b/src/ol/renderer/canvas/VectorTileLayer.js
@@ -663,20 +663,63 @@ class CanvasVectorTileLayerRenderer extends CanvasTileLayerRenderer {
     const replayTypes = VECTOR_REPLAYS[renderMode];
     const viewState = frameState.viewState;
     const rotation = viewState.rotation;
+    const tileSource = layer.getSource();
+    const tileGrid = tileSource.getTileGridForProjection(viewState.projection);
+    const z = tileGrid.getZForResolution(
+      viewState.resolution,
+      tileSource.zDirection
+    );
 
     const tiles = this.renderedTiles;
+    const clips = [];
+    const clipZs = [];
     for (let i = tiles.length - 1; i >= 0; --i) {
       const tile = /** @type {import("../../VectorRenderTile.js").default} */ (
         tiles[i]
       );
+      const executorGroups = tile.executorGroups[getUid(layer)].filter(
+        (group) => group.hasExecutors(replayTypes)
+      );
+      if (executorGroups.length === 0) {
+        continue;
+      }
       const transform = this.getTileRenderTransform(tile, frameState);
-      const executorGroups = tile.executorGroups[getUid(layer)];
+      const currentZ = tile.tileCoord[0];
+      let contextSaved = false;
+      // Clip mask for regions in this tile that already filled by a higher z tile
+      const currentClip = executorGroups[0].getClipCoords(transform);
+      for (let j = 0, jj = clips.length; j < jj; ++j) {
+        if (z !== currentZ && currentZ < clipZs[j]) {
+          const clip = clips[j];
+          if (
+            intersects(
+              [currentClip[0], currentClip[3], currentClip[4], currentClip[7]],
+              [clip[0], clip[3], clip[4], clip[7]]
+            )
+          ) {
+            if (!contextSaved) {
+              context.save();
+              contextSaved = true;
+            }
+            context.beginPath();
+            // counter-clockwise (outer ring) for current tile
+            context.moveTo(currentClip[0], currentClip[1]);
+            context.lineTo(currentClip[2], currentClip[3]);
+            context.lineTo(currentClip[4], currentClip[5]);
+            context.lineTo(currentClip[6], currentClip[7]);
+            // clockwise (inner ring) for higher z tile
+            context.moveTo(clip[6], clip[7]);
+            context.lineTo(clip[4], clip[5]);
+            context.lineTo(clip[2], clip[3]);
+            context.lineTo(clip[0], clip[1]);
+            context.clip();
+          }
+        }
+      }
+      clips.push(currentClip);
+      clipZs.push(currentZ);
       for (let t = 0, tt = executorGroups.length; t < tt; ++t) {
         const executorGroup = executorGroups[t];
-        if (!executorGroup.hasExecutors(replayTypes)) {
-          // sourceTile has no instructions of the types we want to render
-          continue;
-        }
         executorGroup.execute(
           context,
           1,
@@ -686,6 +729,9 @@ class CanvasVectorTileLayerRenderer extends CanvasTileLayerRenderer {
           replayTypes
         );
       }
+      if (contextSaved) {
+        context.restore();
+      }
     }
     context.globalAlpha = alpha;