From 81a50d63306da24944976ad9d1fabd09856f69b5 Mon Sep 17 00:00:00 2001
From: Kartikaya Gupta <kgupta@mozilla.com>
Date: Mon, 23 Apr 2012 23:53:44 -0400
Subject: [PATCH] Bug 737510 - Expand the displayport to fill any partial
 tiles. r=Cwiiis

---
 .../base/gfx/DisplayPortCalculator.java       | 38 ++++++++++++-------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/mobile/android/base/gfx/DisplayPortCalculator.java b/mobile/android/base/gfx/DisplayPortCalculator.java
index 4efe1ddfe851..7de9cc5b0370 100644
--- a/mobile/android/base/gfx/DisplayPortCalculator.java
+++ b/mobile/android/base/gfx/DisplayPortCalculator.java
@@ -8,6 +8,7 @@ package org.mozilla.gecko.gfx;
 import java.util.Map;
 import android.graphics.PointF;
 import android.graphics.RectF;
+import android.util.FloatMath;
 import android.util.Log;
 import org.json.JSONArray;
 import org.mozilla.gecko.FloatUtils;
@@ -17,6 +18,9 @@ final class DisplayPortCalculator {
     private static final String LOGTAG = "GeckoDisplayPortCalculator";
     private static final PointF ZERO_VELOCITY = new PointF(0, 0);
 
+    // Keep this in sync with the TILEDLAYERBUFFER_TILE_SIZE defined in gfx/layers/TiledLayerBuffer.h
+    private static final int TILE_SIZE = 256;
+
     private static final String PREF_DISPLAYPORT_STRATEGY = "gfx.displayport.strategy";
     private static final String PREF_DISPLAYPORT_FM_MULTIPLIER = "gfx.displayport.strategy_fm.multiplier";
     private static final String PREF_DISPLAYPORT_FM_DANGER_X = "gfx.displayport.strategy_fm.danger_x";
@@ -139,6 +143,24 @@ final class DisplayPortCalculator {
         return rect;
     }
 
+    /**
+     * Expand the given margins such that when they are applied on the viewport, the resulting rect
+     * does not have any partial tiles, except when it is clipped by the page bounds. This assumes
+     * the tiles are TILE_SIZE by TILE_SIZE and start at the origin, such that there will always be
+     * a tile at (0,0)-(TILE_SIZE,TILE_SIZE)).
+     */
+    private static DisplayPortMetrics getTileAlignedDisplayPortMetrics(RectF margins, float zoom, ImmutableViewportMetrics metrics) {
+        float left = metrics.viewportRectLeft - margins.left;
+        float top = metrics.viewportRectTop - margins.top;
+        float right = metrics.viewportRectRight + margins.right;
+        float bottom = metrics.viewportRectBottom + margins.bottom;
+        left = Math.max(0.0f, TILE_SIZE * FloatMath.floor(left / TILE_SIZE));
+        top = Math.max(0.0f, TILE_SIZE * FloatMath.floor(top / TILE_SIZE));
+        right = Math.min(metrics.pageSizeWidth, TILE_SIZE * FloatMath.ceil(right / TILE_SIZE));
+        bottom = Math.min(metrics.pageSizeHeight, TILE_SIZE * FloatMath.ceil(bottom / TILE_SIZE));
+        return new DisplayPortMetrics(left, top, right, bottom, zoom);
+    }
+
     /**
      * Adjust the given margins so if they are applied on the viewport in the metrics, the resulting rect
      * does not exceed the page bounds. This code will maintain the total margin amount for a given axis;
@@ -246,15 +268,7 @@ final class DisplayPortCalculator {
             margins.bottom = verticalBuffer - margins.top;
             margins = shiftMarginsForPageBounds(margins, metrics);
 
-            // note that unless the viewport size changes, or the page dimensions change (either because of
-            // content changes or zooming), the size of the display port should remain constant. this
-            // is intentional to avoid re-creating textures and all sorts of other reallocations in the
-            // draw and composition code.
-            return new DisplayPortMetrics(metrics.viewportRectLeft - margins.left,
-                    metrics.viewportRectTop - margins.top,
-                    metrics.viewportRectRight + margins.right,
-                    metrics.viewportRectBottom + margins.bottom,
-                    metrics.zoomFactor);
+            return getTileAlignedDisplayPortMetrics(margins, metrics.zoomFactor, metrics);
         }
 
         public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) {
@@ -363,11 +377,7 @@ final class DisplayPortCalculator {
             RectF margins = velocityBiasedMargins(horizontalBuffer, verticalBuffer, velocity);
             margins = shiftMarginsForPageBounds(margins, metrics);
 
-            return new DisplayPortMetrics(metrics.viewportRectLeft - margins.left,
-                    metrics.viewportRectTop - margins.top,
-                    metrics.viewportRectRight + margins.right,
-                    metrics.viewportRectBottom + margins.bottom,
-                    metrics.zoomFactor);
+            return getTileAlignedDisplayPortMetrics(margins, metrics.zoomFactor, metrics);
         }
 
         public boolean aboutToCheckerboard(ImmutableViewportMetrics metrics, PointF velocity, DisplayPortMetrics displayPort) {