Added zoomScaleExtent method

Closes #71

README.md

@@ -126,6 +126,7 @@ Returns a new graphviz renderer instance on the first element in the given *sele
 | useWorker¹ | true |
 | [width](#graphviz_width) | null |
 | [zoom](#graphviz_zoom) | true |
+| [zoomScaleExtent](#graphviz_zoomScaleExtent) | [0.1, 10] |
 
 ¹ Only has effect when the graphviz renderer instance is created.
 
@@ -332,6 +333,10 @@ A demo of shape tweening can be seen [here](http://bl.ocks.org/magjac/69dc955a2e
 
 If *enable* is true (default), enables panning and zooming, else disables panning and zooming. The zoom behavior is applied to the graph's top level <b>svg</b> element.
 
+<a name="graphviz_zoomScaleExtent" href="#graphviz_zoomScaleExtent">#</a> <i>graphviz</i>.<b>zoomScaleExtent</b>([<i>extent</i>]) [<>](https://github.com/magjac/d3-graphviz/blob/master/src/zoom.js "Source")
+
+Sets the scale extent to the specified array of numbers [k0, k1] where k0 is the minimum allowed scale factor and k1 is the maximum allowed scale factor. The scale extent restricts zooming in and out. For details see [*zoom*.scaleExtent](https://github.com/d3/d3-zoom#zoom_scaleExtent).
+
 <a name="graphviz_resetZoom" href="#graphviz_resetZoom">#</a> <i>graphviz</i>.<b>resetZoom</b>([<i>transition</i>]) [<>](https://github.com/magjac/d3-graphviz/blob/master/src/zoom.js "Source")
 
 Restores the original graph by resetting the transformation made by panning and zooming. If *transition* is specified and not null, it is taken to be a transition instance which is applied during zoom reset.

examples/basic-zoom-fit-window.html

@@ -10,6 +10,7 @@
 margin = 20; // to avoid scrollbars
 
 graphviz = d3.select("#graph").graphviz()
+    .zoomScaleExtent([0.5, 2])
     .attributer(attributer)
     .renderDot('digraph  {a -> b}');
 

src/graphviz.js

@@ -24,6 +24,7 @@ import tweenPrecision from "./tweenPrecision";
 import growEnteringEdges from "./growEnteringEdges";
 import zoom from "./zoom";
 import {resetZoom} from "./zoom";
+import {zoomScaleExtent} from "./zoom";
 import on from "./on";
 import onerror from "./onerror";
 import logEvents from "./logEvents";
@@ -50,6 +51,7 @@ export function Graphviz(selection, options) {
         tweenPrecision: 1,
         growEnteringEdges: true,
         zoom: true,
+        zoomScaleExtent: [0.1, 10],
         width: null,
         height: null,
         scale: 1,
@@ -167,6 +169,7 @@ Graphviz.prototype = graphviz.prototype = {
     growEnteringEdges: growEnteringEdges,
     zoom: zoom,
     resetZoom: resetZoom,
+    zoomScaleExtent: zoomScaleExtent,
     render: render,
     dot: dot,
     renderDot: renderDot,

src/zoom.js

@@ -26,7 +26,7 @@ export function createZoomBehavior() {
         return this;
     }
     this._zoomSelection = svg;
-    var extent = [0.1, 10];
+    var extent = this._options.zoomScaleExtent;
     var zoomBehavior = zoom()
         .scaleExtent(extent)
         .interpolate(interpolate)
@@ -89,3 +89,10 @@ export function resetZoom(transition) {
 
     return this;
 }
+
+export function zoomScaleExtent(extent) {
+
+    this._options.zoomScaleExtent = extent;
+
+    return this;
+}

test/zoom-test.js

@@ -175,3 +175,17 @@ tape("zooming rescales transforms during transitions.", function(test) {
         test.end();
     }
 });
+
+tape("zoomScaleExtent() sets zoom scale extent.", function(test) {
+    var window = global.window = jsdom('<div id="graph"></div>');
+    var document = global.document = window.document;
+    var graphviz = d3_graphviz.graphviz("#graph");
+    var extent = [0.5, 4];
+    graphviz
+        .zoomScaleExtent(extent)
+        .renderDot('digraph {a -> b;}');
+
+    test.equal(graphviz.options().zoomScaleExtent, extent, '.zoomScaleExtent(...) sets zoom scale extent');
+
+    test.end();
+});