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# Graphics

The Graphics module provides a JavaScript API for creating shapes in a variety of formats across a browser test baseline. Based on device and browser capabilities, Graphics leverages SVG, HTML Canvas and VML to render its graphical elements.

The Graphics module features a `Graphic` class that allows you to easily create and manage shapes. Currently, a `Graphic` instance can be used to create predifined shapes and free-form polygons with fill and stroke properties.

## Getting Started

To include the source files for Graphics and its dependencies, first load the YUI seed file if you haven't already loaded it.

    <script src="http://yui.yahooapis.com/3.10.3/build/yui/yui-min.js"></script>

Next, create a new YUI instance for your application and populate it with the modules you need by specifying them as arguments to the `YUI().use()` method. YUI will automatically load any dependencies required by the modules you specify.

    <script>
    // Create a new YUI instance and populate it with the required modules.
    YUI().use('graphics', function (Y) {
        // Graphics is available and ready for use. Add implementation
        // code here.
    });
    </script>

For more information on creating YUI instances and on the `use()` method, see the documentation for the YUI Global Object.

## Using the Graphics module

The `Graphic` class acts a factory and container for shapes. You need at least one `Graphic` instance to create shapes for your application.

### Instantiating A Graphic instance

All you need to instantiate a Graphic instance is an HTML element in which to render. Alternatively, you can attach your instance to the body of your page.

#### CSS

    #mygraphiccontainer {
        width: 600px;
        height: 400px;
    }

#### HTML

    <div id="mygraphiccontainer"></div>

#### JavaScript

    // Instantiate a graphic instance
    var mygraphic = new Y.Graphic({
        render: "#mygraphiccontainer"
    });

By default, `Graphic` will size to its parent container. The API also provides the option of explicitly setting its `width` and `height` attributes. Additionally, the Graphic class provides an `autoSize` attribute. When set to true, the Graphic instance will expand to fit its contents.

### Creating shapes

Shapes are created using the `addShape` method. The `addShape` method takes a config parameter that defines the shape and its properties. When creating a shape, the shape is determined by the `type` attribute. The `Graphics` module includes four pre-defined shapes. They can be created by passing a `String` reference.

key | shape
--- | ---
circle | Y.Circle
ellipse | Y.Ellipse
. rect | Y.Rect
path | Y.Path

Alternatively, you can create your own custom class and pass it directly through the `type` attribute.

The below code would create a 300x200 rectangle with a blue fill and a red border.

    var mygraphic = new Y.Graphic({render:"#mygraphiccontainer"}),
        myrect = mygraphic.addShape({
            type: "rect",
            width: 300,
            height: 200,
            fill: {
                color: "#0000ff"
            },
            stroke: {
                weight: 2,
                color: "#ff0000"
            },
            x: 50,
            y: 100
        });

This code would create an instance of a custom shape that you have created.

    var mygraphic = new Y.Graphic({render:"#mygraphiccontainer"}),
        myrect = mygraphic.addShape({
            type: Y.MyCustomShape,
            width: 300,
            height: 200,
            fill: {
                color: "#0000ff"
            },
            stroke: {
                weight: 2,
                color: "#ff0000"
            },
            x: 50,
            y: 100
        });

### Path Drawing Tool

Read More
Try this simple tool that helps you by generating code while you interactively draw graphic paths.

As you drag the pencil icon, corresponding graphics code is auto-generated. This code can be copied and pasted into a graphics instance to reproduce the paths you created with the pencil.

The violin example was created with this tool.

### Working with the Graphic Class

The `Graphics` module uses different technologies based on browser capabilities. The `Graphics` module normalizes these different technologies with a consistent API. Ideally, you should not have to interact directly with the underlying technologies or their corresponding HTML elements. Both the `Graphic` and `Shape` classes provide APIs for sizing, positioning and customization.

#### Graphic Attributes

The `Graphic` class exposes the following attributes.

Attribute | Type | Description
--- | --- | ---
`id` | `String` | Unique identifier for the `Graphic` instance. If not explicity set, one will be generated.
`shapes` | `Object` | Key value pairs containing all shape instances contained in the `Graphic` instance.
`contentBounds` | `Object` | Object containing size and coordinate data for the content of a Graphic in relation to the coordinate space of the `Graphic` instance. The following values are included: `top`, `right`, `bottom`, `left`, `width` and `height`.
`node` | `HTMLElement` | Outermost HTMLElement of the `Graphic` instance. (read-only)
`width` | `Number` | The width of the `Graphic` instance.
`height` | `Number` | The height of the `Graphic` instance.
`autoSize` | `boolean` | Determines the sizing of the graphic. See the API Docs for possible values and associated behaviors.
`preserveAspectRatio` | `String` | Determines how content is sized when `autoSize` is set to `sizeContentToGraphic`. See the API Docs for possible values.
`resizeDown` | `boolean` | The `contentBounds` will resize to greater values but not to smaller values. (for performance) When resizing the `contentBounds` down is desirable, set the resizeDown value to true. The default value is false.
`x` | `Number` | Indicates the x-coordinate for the instance.
`y` | `Number` | Indicates the y-coordinate for the instance.
`autoDraw` | `boolean` | Indicates whether or not the instance will automatically redraw after a change is made to a shape. When performing multiple operations, such adding many shapes, `autoDraw` can be set to false. Calling `_redraw` will force a redraw when `autoDraw` is `false`.
`visible` | `boolean` | Toggles visibility for a `Graphic` instance.

#### Graphic Methods

The `Graphic` class also has the following public methods.

`Method` | Description
--- | ---
getXY | Returns an array containing the current position of the graphic instance in page coordinates.
addShape | Generates and returns a shape instance by type.
removeShape | Removes a shape instance from from the graphic instance.
removeAllShapes | Removes all shape instances
destroy | Destroys the graphic instance and all its children.
getShapeById | Returns a shape instance based on an id.
batch | Allows for creating multiple shapes in order to batch appending and redraw operations.

### Working with Shapes

#### Shape Attributes

Each shape shares a common set of attributes. Attributes shared across all shapes are listed below:

Attribute | Type | Description
--- | --- | ---
`id` | `String` | Unique identifier for the `Shape` instance. If not explicity set, one will be generated.
`node` | `HTMLElement` | HTMLElement of the `Shape` instance. (read-only)
`data` | `String` | Represents an SVG Path string. This will be parsed and added to shape's API to represent the SVG data across all implementations. Note that when using VML or SVG implementations, part of this content will be added to the DOM using respective VML/SVG attributes. If your content comes from an untrusted source, you will need to ensure that no malicious code is included in that content.
`x` | `Number` | The x-coordinate of the shape.
`y` | `Number` | The y-coordinate of the shape.
`width` | `Number` | The width of the `Shape` instance.
`height` | `Number` | The height of the `Shape` instance.
`visible` | `boolean` | Toggles visibility for a `Shape` instance.
`fill` | `Object` | Contains information about the fill of the shape.
stroke | `Object` | Contains information about the stroke of the shape.
`transformOrigin` | `Array` | The x and y values for the transformOrigin of a transform.
`transform` | `String` | A string containing, in order, transform operations applied to the shape instance. The `transform` string can contain the following values: rotate Rotates the shape clockwise around it transformOrigin. translate Specifies a 2d translation. skew Skews the shape around the x-axis and y-axis. scale Specifies a 2d scaling operation. translateX Translates the shape along the x-axis. translateY Translates the shape along the y-axis. skewX Skews the shape around the x-axis. skewY Skews the shape around the y-axis. Applying transforms through the transform attribute will reset the transform matrix and apply a new transform. The shape class also contains corresponding methods for each transform that will apply the transform to the current matrix. The below code illustrates how you might use the `transform` attribute to instantiate a recangle with a rotation of 45 degrees.
    var myRect = new Y.Rect({
        type:"rect",
        width: 50,
        height: 40,
        transform: "rotate(45)"
    };
The code below would apply `translate` and `rotate` to an existing shape.
    myRect.set("transform", "translate(40, 50) rotate(45)");

#### Shape Methods

Shapes can also be manipulated by the following methods:

Method | Description
--- | ---
`addClass` | Adds a class to the underlying HTMLElement.
`removeClass` | Removes a class to the underlying HTMLElement.
`getXY` | Gets the current position of the shape in page coordinates. Returns an array, `[x, y,]`, with the coordinates.
`setXY` | Sets the current position of the shape in page coordinates. Accepts an array, `[x, y]`, with the coordinates.
`get` | Returns the value of a given attribute.
`set` | Sets the value of an attribute.
`rotate` | Rotates the shape clockwise around it `transformOrigin`.
`translate` | Specifies a 2d translation.
`translateX` | Translates the shape along the x-axis.
`translateY` | Translates the shape along the y-axis.
`skew` | Skews the shape around the x-axis and y-axis.
`skewX` | Skews the shape around the x-axis.
`skewY` | Skews the shape around the y-axis.
`scale` | Specifies a 2d scaling operation.

#### Drawing Methods

Unlike the other included shapes, the `Path` class is not pre-defined. Setting the size, fill and/or stroke of a pre-defined shape will render the shape. This is not true with the `Path`. To render a `Path` instance, its drawing methods need to be leveraged. These drawing methods can also be leveraged when creating custom shapes. Available drawing methods include:

moveTo
  Moves to a coordinate point without drawing a line.
lineTo
  Draws a line segment from the current point to the specified point.
curveTo
  Draws a curve based on a start point, end point and two control points.
quadraticCurveTo
  Draws a quadratic curve based on a start point, end point and two control points.
end
  Ends a drawing operation. The path or custom shape will draw after end is called.
clear
  Clears all contents of a path or custom shape.

#### Strokes and Fills

All `Shape` instances contain `stroke` and `fill` attributes. They are used to define the colors for a `Shape`.

##### Defining a Stroke

The `stroke` attribute has six properties.

color
  The color of the stroke.
weight
  Number that indicates the width of the stroke.
opacity
  Number between 0 and 1 that indicates the opacity of the stroke. The default value is 1.
dashstyle
Indicates whether to draw a dashed stroke. When set to "none", a solid stroke is drawn. When set to an array, the first index indicates the length of the dash. The second index indicates the length of gap.
linecap
  Specifies the linecap for the stroke. The following values can be specified:
  butt (default)
    Specifies a butt linecap.
  square
    Specifies a sqare linecap.
  round
    Specifies a round linecap.
linejoin
  Specifies a linejoin for the stroke. The following values can be specified:
  round (default)
    Specifies that the linejoin will be round.
  bevel
    Specifies a bevel for the linejoin.
  miter limit
    An integer specifying the miter limit of a miter linejoin. If you want to specify a linejoin of miter, you simply specify the limit as opposed to having separate miter and miter limit values.

The code below would set a 2 pixel solid red stroke on `myshape`.

    myshape.set("stroke", {
        color: "#ff0000",
        weight: 2
    });

The `dashstyle` property can be used to create a dashed stroke on a shape.

    myshape.set("stroke", {
        color: "#ff0000",
        weight: 2,
        dashstyle: [3, 2]
    });

##### Defining a Fill

The `fill` attribute has the following properties.

color
  The color of the fill.
opacity
  Number between 0 and 1 that indicates the opacity of the fill. The default value is 1.
type
  Type of fill.
  solid
    Solid single color fill. (default)
  linear
    Linear gradient fill.
  radial
    Radial gradient fill.

If a `linear` or `radial` is specified as the fill type. The following additional property is used:

stops
  An array of objects containing the following properties:
  color
    The color of the stop.
  opacity
    Number between 0 and 1 that indicates the opacity of the stop. The default value is 1. Note: No effect for IE <= 8
  offset
    Number between 0 and 1 indicating where the color stop is positioned.

Linear gradients also have the following property:

rotation
  Linear gradients flow left to right by default. The rotation property allows you to change the flow by rotation. (e.g. A rotation of 180 would make the gradient pain from right to left.)

Radial gradients have the following additional properties:

r
  Radius of the gradient circle.
fx
  Focal point x-coordinate of the gradient.
fy
  Focal point y-coordinate of the gradient.
cx
  The x-coordinate of the center of the gradient circle. Determines where the color stop begins. The default value 0.5.

  Note: This property currently has no effect on Android or IE 6 - 8.

cy
  The y-coordinate of the center of the gradient circle. Determines where the color stop begins. The default value 0.5.

  Note: This property currently has no effect on Android or IE 6 - 8.

### Radial Gradient Tool

Try this simple tool that helps you interactively preview radial gradient fills.
Try It

Avoid the trial and error, quickly get just the look you want. As you drag and resize different parts of the control, you preview the radial gradient fill and see its property values update. Click the "Get Code Snippet" button for code you can paste into a Graphics instance to reproduce the same gradient.

## Known Issues

- Gradients need more need more normalization across technologies. Certain gradient types have limitations on different browsers.

  - Radial gradients contain the properties `cx` and `cy`. These properties currently have no impact on Android or IE 6 - 8.
  - After being initially set, gradients cannot be updated in IE 6 - 8.

- Path element currently lacks the ability to have interactivity in Android.