diff --git a/src/webgldrawer.js b/src/webgldrawer.js
index 2a9740fd..0d34e299 100644
--- a/src/webgldrawer.js
+++ b/src/webgldrawer.js
@@ -214,8 +214,8 @@
                                         tiledImage._croppingPolygons ||
                                         tiledImage.debugMode
                                     );
-                let useTwoPassRendering = useContext2dPipeline || (tiledImage.opacity < 1); // TODO: check hasTransparency in addition to opacity
 
+                let useTwoPassRendering = useContext2dPipeline || (tiledImage.opacity < 1); // TODO: check hasTransparency in addition to opacity
 
                 let tilesToDraw = tiledImage.getTilesToDraw();
 
@@ -276,20 +276,21 @@
                 // iterate over tiles and add data for each one to the buffers
                 for(let tileIndex = 0; tileIndex < tilesToDraw.length; tileIndex++){
                     let tile = tilesToDraw[tileIndex].tile;
-                    let index = tileIndex % maxTextures;
+                    let indexInDrawArray = tileIndex % maxTextures;
+                    let numTilesToDraw =  indexInDrawArray + 1;
                     let tileContext = tile.getCanvasContext();
 
                     let textureInfo = tileContext ? this._TextureMap.get(tileContext.canvas) : null;
                     if(textureInfo){
-                        this._getTileData(tile, tiledImage, textureInfo, overallMatrix, index, texturePositionArray, textureDataArray, matrixArray, opacityArray);
+                        this._getTileData(tile, tiledImage, textureInfo, overallMatrix, indexInDrawArray, texturePositionArray, textureDataArray, matrixArray, opacityArray);
                     } else {
                         // console.log('No tile info', tile);
                     }
-                    if( (index === maxTextures - 1) || (tileIndex === tilesToDraw.length - 1)){
+                    if( (numTilesToDraw === maxTextures) || (tileIndex === tilesToDraw.length - 1)){
                         // We've filled up the buffers: time to draw this set of tiles
 
                         // bind each tile's texture to the appropriate gl.TEXTURE#
-                        for(let i = 0; i <= index; i++){
+                        for(let i = 0; i <= numTilesToDraw; i++){
                             gl.activeTexture(gl.TEXTURE0 + i);
                             gl.bindTexture(gl.TEXTURE_2D, textureDataArray[i]);
                         }
@@ -316,7 +317,7 @@
                         gl.vertexAttribPointer(this._firstPass.aIndex, 1, gl.FLOAT, false, 0, 0);
 
                         // Draw! 6 vertices per tile (2 triangles per rectangle)
-                        gl.drawArrays(gl.TRIANGLES, 0, 6 * (index + 1) );
+                        gl.drawArrays(gl.TRIANGLES, 0, 6 * numTilesToDraw );
                     }
                 }
 
@@ -391,7 +392,7 @@
                 }
 
             });
-            // TODO: the line below is a test!
+
             if(renderingBufferHasImageData){
                 this._outputContext.drawImage(this._renderingCanvas, 0, 0);
             }
diff --git a/test/demo/drawerperformance.js b/test/demo/drawerperformance.js
index 66908e08..56d1b4fc 100644
--- a/test/demo/drawerperformance.js
+++ b/test/demo/drawerperformance.js
@@ -15,15 +15,218 @@ const labels = {
 }
 let viewer;
 
+/**
+ * based on https://github.com/mrdoob/stats.js/ by @author mrdoob / http://mrdoob.com/
+ */
+
+class Stats{
+    constructor(){
+        this.mode = 0;
+
+        var container = this.container = document.createElement( 'div' );
+        container.style.cssText = 'position:fixed;top:0;left:0;cursor:pointer;opacity:0.9;z-index:10000';
+        container.addEventListener( 'click', function ( event ) {
+
+            event.preventDefault();
+            showPanel( ++ mode % container.children.length );
+
+        }, false );
+
+
+		this.dom = container;
+
+        this.started = false;
+
+        this.fpsPanel = this.addPanel( new Stats.Panel( 'FPS', '#0ff', '#002' ) );
+        this.msPanel = this.addPanel( new Stats.Panel( 'MS', '#0f0', '#020' ) );
+        this.mspsPanel = this.addPanel( new Stats.Panel( 'MSPS', '#0f0', '#020' ) );
+
+        if ( window.performance && window.performance.memory ) {
+
+            this.memPanel = this.addPanel( new Stats.Panel( 'MB', '#f08', '#201' ) );
+
+        }
+
+        this.showPanel( 0 );
+    }
+
+
+	//
+
+	addPanel( panel ) {
+
+		this.container.appendChild( panel.dom );
+		return panel;
+
+	}
+
+	showPanel( id ) {
+
+		for ( var i = 0; i < this.container.children.length; i ++ ) {
+
+			this.container.children[ i ].style.display = i === id ? 'block' : 'none';
+
+		}
+
+		this.mode = id;
+
+	}
+
+	//
+
+
+    begin() {
+
+        this.beginTime = ( performance || Date ).now();
+
+        if(!this.started){
+            this.started = true;
+            this.prevTime = this.beginTime;
+            this.frames = 0;
+            this.cumulativeMS = 0;
+        }
+    }
+
+    end() {
+
+        this.frames ++;
+
+        var time = ( performance || Date ).now();
+
+        var interval = time - this.beginTime;
+
+        this.cumulativeMS += interval;
+
+        this.msPanel.update( interval, 200 );
+
+        if ( time >= this.prevTime + 1000 ) {
+
+            this.fpsPanel.update( ( this.frames * 1000 ) / ( time - this.prevTime ), 130 );
+
+            this.mspsPanel.update( ( this.cumulativeMS * 1000 ) / ( time - this.prevTime ), 1100 );
+
+            this.prevTime = time;
+            this.frames = 0;
+            this.cumulativeMS = 0;
+
+            if ( this.memPanel ) {
+
+                var memory = performance.memory;
+                this.memPanel.update( memory.usedJSHeapSize / 1048576, memory.jsHeapSizeLimit / 1048576 );
+
+            }
+
+        }
+
+        return time;
+
+    }
+
+    update() {
+
+        this.beginTime = this.end();
+
+    }
+
+
+};
+
+Stats.Panel = function ( name, fg, bg ) {
+
+	var min = Infinity, max = 0, round = Math.round;
+	var PR = round( window.devicePixelRatio || 1 );
+
+	var WIDTH = 80 * PR, HEIGHT = 48 * PR,
+			TEXT_X = 3 * PR, TEXT_Y = 2 * PR,
+			GRAPH_X = 3 * PR, GRAPH_Y = 15 * PR,
+			GRAPH_WIDTH = 74 * PR, GRAPH_HEIGHT = 30 * PR;
+
+	var canvas = document.createElement( 'canvas' );
+	canvas.width = WIDTH;
+	canvas.height = HEIGHT;
+	canvas.style.cssText = 'width:80px;height:48px';
+
+	var context = canvas.getContext( '2d' );
+	context.font = 'bold ' + ( 9 * PR ) + 'px Helvetica,Arial,sans-serif';
+	context.textBaseline = 'top';
+
+	context.fillStyle = bg;
+	context.fillRect( 0, 0, WIDTH, HEIGHT );
+
+	context.fillStyle = fg;
+	context.fillText( name, TEXT_X, TEXT_Y );
+	context.fillRect( GRAPH_X, GRAPH_Y, GRAPH_WIDTH, GRAPH_HEIGHT );
+
+	context.fillStyle = bg;
+	context.globalAlpha = 0.9;
+	context.fillRect( GRAPH_X, GRAPH_Y, GRAPH_WIDTH, GRAPH_HEIGHT );
+
+	return {
+
+		dom: canvas,
+
+		update: function ( value, maxValue ) {
+
+			min = Math.min( min, value );
+			max = Math.max( max, value );
+
+			context.fillStyle = bg;
+			context.globalAlpha = 1;
+			context.fillRect( 0, 0, WIDTH, GRAPH_Y );
+			context.fillStyle = fg;
+			context.fillText( round( value ) + ' ' + name + ' (' + round( min ) + '-' + round( max ) + ')', TEXT_X, TEXT_Y );
+
+			context.drawImage( canvas, GRAPH_X + PR, GRAPH_Y, GRAPH_WIDTH - PR, GRAPH_HEIGHT, GRAPH_X, GRAPH_Y, GRAPH_WIDTH - PR, GRAPH_HEIGHT );
+
+			context.fillRect( GRAPH_X + GRAPH_WIDTH - PR, GRAPH_Y, PR, GRAPH_HEIGHT );
+
+			context.fillStyle = bg;
+			context.globalAlpha = 0.9;
+			context.fillRect( GRAPH_X + GRAPH_WIDTH - PR, GRAPH_Y, PR, round( ( 1 - ( value / maxValue ) ) * GRAPH_HEIGHT ) );
+
+		}
+
+	};
+
+};
+
+
 (function(){
-    var script=document.createElement('script');
-    script.onload=function(){
-        var stats=new Stats();
-        document.body.appendChild(stats.dom);
-        requestAnimationFrame(function loop(){stats.update();requestAnimationFrame(loop)});
+
+
+    let fpscontainer = $('<div>',{style:'position:fixed;top:0;left:0;'}).appendTo('body');
+    let labels=$('<div>',{style:'display:grid;grid-template-columns:1fr 1fr 1fr;justify-items:center;'}).appendTo(fpscontainer);
+    $('<label>').text('FPS').appendTo(labels);
+    $('<label>').text('Update (ms)').appendTo(labels);
+    $('<label>').text('Draw (ms)').appendTo(labels);
+    var statsFPS=new Stats();
+    statsFPS.begin();
+    $(statsFPS.dom).css({position:'relative', display:'inline-block'}).appendTo(fpscontainer);
+    requestAnimationFrame(function loop(){statsFPS.update();requestAnimationFrame(loop)});
+
+    var statsUpdate=new Stats();
+    $(statsUpdate.dom).css({position:'relative', display:'inline-block'}).appendTo(fpscontainer);
+    statsUpdate.showPanel(2);
+
+    var statsDraw=new Stats();
+    $(statsDraw.dom).css({position:'relative', display:'inline-block'}).appendTo(fpscontainer);
+    statsDraw.showPanel(2);
+
+    let origUpdate = OpenSeadragon.World.prototype.update;
+    let origDraw = OpenSeadragon.World.prototype.draw;
+
+    OpenSeadragon.World.prototype.update = function(){
+        statsUpdate.begin();
+        origUpdate.call(this, ...arguments);
+        statsUpdate.end();
     };
-    script.src='https://mrdoob.github.io/stats.js/build/stats.min.js';
-    document.head.appendChild(script);
+
+    OpenSeadragon.World.prototype.draw = function(){
+        statsDraw.begin();
+        origDraw.call(this, ...arguments);
+        statsDraw.end();
+    }
+
 })();
 
 
@@ -57,7 +260,7 @@ function run(drawerType, num) {
         let m = movingLeft ? 1 : -1;
         movingLeft = m === -1;
         let dist = viewer.viewport.getBounds().width;
-        viewer.viewport.panBy(new OpenSeadragon.Point( dist * m/2, 0));
+        viewer.viewport.panBy(new OpenSeadragon.Point( dist * m/4, 0));
 
     }, 1000);
 }
@@ -90,3 +293,4 @@ function makeTileSources(num){
     })
 
 }
+
diff --git a/test/demo/webgldemodrawer.js b/test/demo/webgldemodrawer.js
index 095e228b..e6d86f04 100644
--- a/test/demo/webgldemodrawer.js
+++ b/test/demo/webgldemodrawer.js
@@ -302,8 +302,8 @@
                                         tiledImage._croppingPolygons ||
                                         tiledImage.debugMode
                                     );
-              
-                let useTwoPassRendering = useContext2dPipeline ||(tiledImage.opacity < 1); // TODO: check hasTransparency in addition to opacity
+
+                let useTwoPassRendering = useContext2dPipeline || (tiledImage.opacity < 1); // TODO: check hasTransparency in addition to opacity
 
                 let tilesToDraw = tiledImage.getTilesToDraw();
 
@@ -364,20 +364,21 @@
                 // iterate over tiles and add data for each one to the buffers
                 for(let tileIndex = 0; tileIndex < tilesToDraw.length; tileIndex++){
                     let tile = tilesToDraw[tileIndex].tile;
-                    let index = tileIndex % maxTextures;
+                    let indexInDrawArray = tileIndex % maxTextures;
+                    let numTilesToDraw =  indexInDrawArray + 1;
                     let tileContext = tile.getCanvasContext();
 
                     let textureInfo = tileContext ? this._TextureMap.get(tileContext.canvas) : null;
                     if(textureInfo){
-                        this._getTileData(tile, tiledImage, textureInfo, overallMatrix, index, texturePositionArray, textureDataArray, matrixArray, opacityArray);
+                        this._getTileData(tile, tiledImage, textureInfo, overallMatrix, indexInDrawArray, texturePositionArray, textureDataArray, matrixArray, opacityArray);
                     } else {
                         // console.log('No tile info', tile);
                     }
-                    if( (index === maxTextures - 1) || (tileIndex === tilesToDraw.length - 1)){
+                    if( (numTilesToDraw === maxTextures) || (tileIndex === tilesToDraw.length - 1)){
                         // We've filled up the buffers: time to draw this set of tiles
 
                         // bind each tile's texture to the appropriate gl.TEXTURE#
-                        for(let i = 0; i <= index; i++){
+                        for(let i = 0; i <= numTilesToDraw; i++){
                             gl.activeTexture(gl.TEXTURE0 + i);
                             gl.bindTexture(gl.TEXTURE_2D, textureDataArray[i]);
                         }
@@ -404,7 +405,7 @@
                         gl.vertexAttribPointer(this._firstPass.aIndex, 1, gl.FLOAT, false, 0, 0);
 
                         // Draw! 6 vertices per tile (2 triangles per rectangle)
-                        gl.drawArrays(gl.TRIANGLES, 0, 6 * (index + 1) );
+                        gl.drawArrays(gl.TRIANGLES, 0, 6 * numTilesToDraw );
                     }
                 }
 
@@ -479,7 +480,7 @@
                 }
 
             });
-            // TODO: the line below is a test!
+
             if(renderingBufferHasImageData){
                 this._outputContext.drawImage(this._renderingCanvas, 0, 0);
             }