From 05b6ca05fe69b9d30705660fa3996c053210ecb1 Mon Sep 17 00:00:00 2001
From: Tom Payne <twpayne@gmail.com>
Date: Tue, 7 Aug 2012 17:46:06 +0200
Subject: [PATCH] Improve WebGL pixel precision

---
 src/ol/webgl/tilelayerrenderer.js | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/ol/webgl/tilelayerrenderer.js b/src/ol/webgl/tilelayerrenderer.js
index a93ac9f8ce..0929c9563c 100644
--- a/src/ol/webgl/tilelayerrenderer.js
+++ b/src/ol/webgl/tilelayerrenderer.js
@@ -374,8 +374,8 @@ ol.webgl.TileLayerRenderer.prototype.render = function() {
   var zs = goog.object.getKeys(tilesToDrawByZ);
   goog.array.sort(zs);
   var uTileOffset = goog.vec.Vec4.createFloat32();
-  goog.array.forEach(zs, function(z) {
-    goog.object.forEach(tilesToDrawByZ[z], function(tile) {
+  goog.array.forEach(zs, function(tileZ) {
+    goog.object.forEach(tilesToDrawByZ[tileZ], function(tile) {
       var tileExtent = tileGrid.getTileCoordExtent(tile.tileCoord);
       var sx = 2 * tileExtent.getWidth() / framebufferExtentSize.width;
       var sy = 2 * tileExtent.getHeight() / framebufferExtentSize.height;
@@ -383,10 +383,17 @@ ol.webgl.TileLayerRenderer.prototype.render = function() {
           framebufferExtentSize.width - 1;
       var ty = 2 * (tileExtent.minY - framebufferExtent.minY) /
           framebufferExtentSize.height - 1;
+      var filter;
+      if (tileZ == z) {
+        tx += 0.5 * sx / tileSize.width;
+        ty += 0.5 * sy / tileSize.height;
+        filter = goog.webgl.NEAREST;
+      } else {
+        filter = goog.webgl.LINEAR;
+      }
       goog.vec.Vec4.setFromValues(uTileOffset, sx, sy, tx, ty);
       gl.uniform4fv(this.locations_.uTileOffset, uTileOffset);
-      map.bindImageTexture(
-          tile.getImage(), goog.webgl.LINEAR, goog.webgl.LINEAR);
+      map.bindImageTexture(tile.getImage(), filter, filter);
       gl.drawArrays(goog.webgl.TRIANGLE_STRIP, 0, 4);
     }, this);
   }, this);
@@ -412,8 +419,8 @@ ol.webgl.TileLayerRenderer.prototype.render = function() {
         1);
   }
   goog.vec.Mat4.translate(this.matrix_,
-      -0.5,
-      -0.5,
+      -0.5 - 0.5 / framebufferDimension,
+      -0.5 - 0.5 / framebufferDimension,
       0);
 
 };