The annotations feature brings presentation style functionality to RGraph charts. You can use this feature for highlighting your charts if you need to.
Enabling annotations is a very simple affair, and consists of doing the following:
myGraph.Set('chart.annotatable', true);
Annotations are supported in all browsers that RGraph works with - Firefox 3.5+, Chrome 2+, Safari 4+, Opera 10.5+ and MSIE/Google Chrome Frame. They DO NOT however work with MSIE 8/ExCanvas.
As mentioned you can use it for presentations, highlighting things to yourself or others or just to have fun drawing (!).
That depends on which browser you're using. The annotation data is stored in the users web browser (not on the web server), meaning currently (21st March 2010) browser support is limited to Firefox 3.5+, Safari 4+, Chrome 4+ and Opera 10.5+. MSIE 8 also has the required storage capabilities, but since it doesn't yet support canvas, the point is moot. The user does not have to confirm anything for storage to be allowed - try it out on this page by drawing on the chart and then refreshing the page.
You can show the palette by using the RGraph.Showpalette function shown below as a context menu item:
myObj.Set('chart.contextmenu', [
['Show palette', RGraph.Showpalette],
['Clear', function () {RGraph.Clear(myObj.canvas); myObj.Draw();}]
]);
This code will result in the same context menu as the chart above.
RGraph.Clear(myGraph.canvas); // Clear the chart myGraph.Draw(); // Redraw it
In the chart above, there is a context menu that allows you to both clear the chart and also demonstrates the mini-palette feature available to you.
When annotations are not enabled, any prior annotations that may have been made are not displayed. To show them you need to use the API function RGraph.ReplayAnnotations(object) after the call to .Draw().
With a little bit of custom Javascript and some server side scripting you can make your annotations persist across different browsers/computers. You can find an example of this here.