Fix Issue 328:Thick data lines shown breaks

[dygraphs.git] / auto_tests / tests / PixelSampler.js

diff --git a/auto_tests/tests/PixelSampler.js b/auto_tests/tests/PixelSampler.js
new file mode 100644 (file)
index 0000000..89c520f
--- /dev/null
+++ b/auto_tests/tests/PixelSampler.js
@@ -0,0 +1,46 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+
+/**
+ * @fileoverview A class to facilitate sampling colors at particular pixels on a
+ * dygraph.
+ * @author danvk@google.com (Dan Vanderkam)
+ */
+
+'use strict';
+
+/**
+ * @constructor
+ */
+var PixelSampler = function(dygraph) {
+  this.dygraph_ = dygraph;
+
+  var canvas = dygraph.hidden_;
+  var ctx = canvas.getContext("2d");
+  this.imageData_ = ctx.getImageData(0, 0, canvas.width, canvas.height);
+};
+
+/**
+ * @param {number} x The screen x-coordinate at which to sample.
+ * @param {number} y The screen y-coordinate at which to sample.
+ * @return {Array.<number>} a 4D array: [R, G, B, alpha]. All four values
+ * are in [0, 255]. A pixel which has never been touched will be [0,0,0,0].
+ */
+PixelSampler.prototype.colorAtPixel = function(x, y) {
+  var i = 4 * (x + this.imageData_.width * y);
+  var d = this.imageData_.data;
+  return [d[i], d[i+1], d[i+2], d[i+3]];
+};
+
+/**
+ * The method samples a color using data coordinates (not screen coordinates).
+ * This will round your data coordinates to the nearest screen pixel before
+ * sampling.
+ * @param {number} x The data x-coordinate at which to sample.
+ * @param {number} y The data y-coordinate at which to sample.
+ * @return {Array.<number>} a 4D array: [R, G, B, alpha]. All four values
+ * are in [0, 255]. A pixel which has never been touched will be [0,0,0,0].
+ */
+PixelSampler.prototype.colorAtCoordinate = function(x, y) {
+  var dom_xy = this.dygraph_.toDomCoords(x, y);
+  return this.colorAtPixel(Math.round(dom_xy[0]), Math.round(dom_xy[1]));
+};