#

API Documentation for: 0.8.1
Show: Inherited Protected Private Deprecated

# AlphaMapFilter Class

Extends Filter
Defined in: `AlphaMapFilter:41`
Module: EaselJS

Applies a greyscale alpha map image (or canvas) to the target, such that the alpha channel of the result will be copied from the red channel of the map, and the RGB channels will be copied from the target.

Generally, it is recommended that you use AlphaMaskFilter, because it has much better performance.

#### Example

This example draws a red->blue box, caches it, and then uses the cache canvas as an alpha map on a 100x100 image.

      var box = new createjs.Shape();
      box.graphics.beginLinearGradientFill(["#ff0000", "#0000ff"], [0, 1], 0, 0, 0, 100)
      box.graphics.drawRect(0, 0, 100, 100);
      box.cache(0, 0, 100, 100);

      var bmp = new createjs.Bitmap("path/to/image.jpg");
      bmp.filters = [
          new createjs.AlphaMapFilter(box.cacheCanvas)
      ];
      bmp.cache(0, 0, 100, 100);
      stage.addChild(bmp);

See Filter for more information on applying filters.

## Constructor

### `AlphaMapFilter`

(

- `alphaMap`

)

Defined in `AlphaMapFilter:41`

#### Parameters:

- `alphaMap` HTMLImageElement | HTMLCanvasElement

  The greyscale image (or canvas) to use as the alpha value for the result. This should be exactly the same dimensions as the target.

- Index
- Methods
- Properties

## Item Index

### Methods

- _applyFilter
- _prepAlphaMap
- applyFilter
- clone
- getBounds
- initialize deprecated
- toString

### Properties

- _alphaMap
- _mapData
- alphaMap

## Methods

### `_applyFilter`

(

- `imageData`

)
Boolean

Inherited from Filter: `_applyFilter:148`

#### Parameters:

- `imageData` ImageData

  Target ImageData instance.

#### Returns:

Boolean:

### `_prepAlphaMap`

() protected

Defined in `_prepAlphaMap:133`

### `applyFilter`

(

- `ctx`
- `x`
- `y`
- `width`
- `height`
- `[targetCtx]`
- `[targetX]`
- `[targetY]`

)
Boolean

Inherited from Filter: `applyFilter:99`

Applies the filter to the specified context.

#### Parameters:

- `ctx` CanvasRenderingContext2D

  The 2D context to use as the source.

- `x` Number

  The x position to use for the source rect.

- `y` Number

  The y position to use for the source rect.

- `width` Number

  The width to use for the source rect.

- `height` Number

  The height to use for the source rect.

- `[targetCtx]` CanvasRenderingContext2D optional

  The 2D context to draw the result to. Defaults to the context passed to ctx.

- `[targetX]` Number optional

  The x position to draw the result to. Defaults to the value passed to x.

- `[targetY]` Number optional

  The y position to draw the result to. Defaults to the value passed to y.

#### Returns:

Boolean:

If the filter was applied successfully.

### `clone`

() Filter

Inherited from Filter: `clone:138`

Returns a clone of this Filter instance.

#### Returns:

Filter:

A clone of the current Filter instance.

### `getBounds`

(

- `[rect]`

)
Rectangle

Inherited from Filter: `getBounds:89`

Provides padding values for this filter. That is, how much the filter will extend the visual bounds of an object it is applied to.

#### Parameters:

- `[rect]` Rectangle optional

  If specified, the provided Rectangle instance will be expanded by the padding amounts and returned.

#### Returns:

Rectangle:

If a `rect` param was provided, it is returned. If not, either a new rectangle with the padding values, or null if no padding is required for this filter.

### `initialize`

() deprecated protected

Inherited from Filter: `initialize:74`

REMOVED. Removed in favor of using `MySuperClass_constructor`. See extend and promote for details.

There is an inheritance tutorial distributed with EaselJS in /tutorials/Inheritance.

### `toString`

() String

Inherited from Filter: `toString:129`

Returns a string representation of this object.

#### Returns:

String:

a string representation of the instance.

## Properties

### `_alphaMap`

HTMLImageElement | HTMLCanvasElement protected

Defined in `_alphaMap:84`

### `_mapData`

Uint8ClampedArray protected

Defined in `_mapData:91`

### `alphaMap`

HTMLImageElement | HTMLCanvasElement

Defined in `alphaMap:74`

The greyscale image (or canvas) to use as the alpha value for the result. This should be exactly the same dimensions as the target.