X-Git-Url: https://adrianiainlam.tk/git/?a=blobdiff_plain;f=dygraph-canvas.js;h=450c8a9f396e9535a2849f1af8bf7147a3edd077;hb=13f8b0472ff8e7336bdf56f69ff838a1f3e76162;hp=a8b9807d92dfd5dde6a82cbcf6c76cb9cadb9fd2;hpb=c560c848f1334c9dadaf5ac7b70dec6f4bd45c00;p=dygraphs.git

diff --git a/dygraph-canvas.js b/dygraph-canvas.js
index a8b9807..450c8a9 100644
--- a/dygraph-canvas.js
+++ b/dygraph-canvas.js
@@ -243,7 +243,6 @@ DygraphCanvasRenderer._predicateThatSkipsEmptyPoints =
 };
 
 /**
- *
  * @private
  */
 DygraphCanvasRenderer.prototype._drawStyledLine = function(
@@ -306,6 +305,7 @@ DygraphCanvasRenderer.prototype._drawSeries = function(
   ctx.strokeStyle = color;
   ctx.lineWidth = strokeWidth;
 
+  // NOTE: we break the iterator's encapsulation here for about a 25% speedup.
   var arr = iter.array_;
   var limit = iter.end_;
   var predicate = iter.predicate_;
@@ -354,6 +354,8 @@ DygraphCanvasRenderer.prototype._drawSeries = function(
             ctx.lineTo(point.canvasx, prevCanvasY);
             prevCanvasX = point.canvasx;
           }
+
+          // TODO(danvk): this moveTo is rarely necessary
           ctx.moveTo(prevCanvasX, prevCanvasY);
           ctx.lineTo(point.canvasx, point.canvasy);
         }
@@ -419,6 +421,12 @@ DygraphCanvasRenderer.prototype._renderLineChart = function() {
   // TODO(bhs): this loop is a hot-spot for high-point-count charts. These
   // transformations can be pushed into the canvas via linear transformation
   // matrices.
+  // NOTE(danvk): this is trickier than it sounds at first. The transformation
+  // needs to be done before the .moveTo() and .lineTo() calls, but must be
+  // undone before the .stroke() call to ensure that the stroke width is
+  // unaffected.  An alternative is to reduce the stroke width in the
+  // transformed coordinate space, but you can't specify different values for
+  // each dimension (as you can with .scale()). The speedup here is ~12%.
   var points = this.layout.points;
   for (i = points.length; i--;) {
     var point = points[i];
@@ -495,7 +503,6 @@ DygraphCanvasRenderer.prototype.drawErrorBars_ = function(points) {
         continue;
       }
 
-      // TODO(danvk): here
       if (stepPlot) {
         newYs = [ point.y_bottom, point.y_top ];
         prevY = point.y;