android: remove tiles delayed by one redraw call

Change-Id: I5ab5e4a0ba9cdf3f3115c4913b4cf04e7f062755

android/experimental/LOAndroid3/src/java/org/mozilla/gecko/gfx/MultiTileLayer.java

@@ -45,6 +45,7 @@ import android.graphics.Region;
 import android.util.Log;
 
 import org.libreoffice.TileProvider;
+import org.mozilla.gecko.util.FloatUtils;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -230,7 +231,6 @@ public class MultiTileLayer extends Layer {
     public void reevaluateTiles(ImmutableViewportMetrics viewportMetrics) {
         if (currentZoomFactor != viewportMetrics.zoomFactor) {
             currentZoomFactor = viewportMetrics.zoomFactor;
-            mTiles.clear();
         }
 
         RectF newTileViewPort = inflate(roundToTileSize(viewportMetrics.getViewport(), TILE_SIZE), TILE_SIZE);
@@ -239,11 +239,23 @@ public class MultiTileLayer extends Layer {
 
         if (tileViewPort != newTileViewPort) {
             tileViewPort = newTileViewPort;
-            clearTiles();
+            cleanTiles();
             addNewTiles();
+            markTiles();
         }
     }
 
+    private void cleanTiles() {
+        List<SubTile> tilesToRemove = new ArrayList<SubTile>();
+        for(SubTile tile : mTiles) {
+            if (tile.markedForRemoval) {
+                tile.destroy();
+                tilesToRemove.add(tile);
+            }
+        }
+        mTiles.removeAll(tilesToRemove);
+    }
+
     private void addNewTiles() {
         for (float y = tileViewPort.top; y < tileViewPort.bottom; y += TILE_SIZE) {
             if (y > currentPageSize.height) {
@@ -269,17 +281,17 @@ public class MultiTileLayer extends Layer {
         }
     }
 
-    private void clearTiles() {
-        ArrayList<SubTile> removeTiles = new ArrayList<SubTile>();
+    private void markTiles() {
         for (SubTile tile : mTiles) {
-            RectF tileRect = new RectF(tile.x, tile.y, tile.x + TILE_SIZE, tile.y + TILE_SIZE);
-            if (!RectF.intersects(tileViewPort, tileRect)) {
-                tile.destroy();
-                removeTiles.add(tile);
+            if (FloatUtils.fuzzyEquals(tile.zoom, currentZoomFactor)) {
+                RectF tileRect = new RectF(tile.x, tile.y, tile.x + TILE_SIZE, tile.y + TILE_SIZE);
+                if (!RectF.intersects(tileViewPort, tileRect)) {
+                    tile.markForRemoval();
+                }
+            } else {
+                tile.markForRemoval();
             }
         }
-
-        mTiles.removeAll(removeTiles);
     }
 }
 

android/experimental/LOAndroid3/src/java/org/mozilla/gecko/gfx/SubTile.java

@@ -10,10 +10,16 @@ public class SubTile extends SingleTileLayer {
     public int y;
     public float zoom;
 
+    public boolean markedForRemoval = false;
+
     public SubTile(CairoImage mImage, int x, int y, float zoom) {
         super(mImage);
         this.x = x;
         this.y = y;
         this.zoom = zoom;
     }
+
+    public void markForRemoval() {
+        markedForRemoval = true;
+    }
 }