#

API Documentation for: NEXT
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
- shaderParamSetup
- toString

### Properties

- _alphaMap
- _mapData
- _multiPass
- alphaMap
- FRAG_SHADER
- usesContext
- VTX_SHADER

## Methods

### `_applyFilter`

(

- `imageData`

)
Boolean

Inherited from Filter: `_applyFilter:180`

#### Parameters:

- `imageData` ImageData

  Target ImageData instance.

#### Returns:

Boolean:

### `_prepAlphaMap`

() protected

Defined in `_prepAlphaMap:161`

### `applyFilter`

(

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

)
Boolean

Inherited from Filter: `applyFilter:131`

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:170`

Returns a clone of this Filter instance.

#### Returns:

Filter:

A clone of the current Filter instance.

### `getBounds`

(

- `[rect]`

)
Rectangle

Inherited from Filter: `getBounds:111`

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.

### `shaderParamSetup`

(

- `gl`
- `stage`
- `shaderProgram`

)

Inherited from Filter: `shaderParamSetup:121`

Assign any unique uniforms or other setup functionality here.

#### Parameters:

- `gl` WebGLContext

  The context associated with the stage performing the render.

- `stage` StageGL

  The stage instance that will be rendering.

- `shaderProgram` ShaderProgram

  The compiled shader that is going to be used to perform the render.

### `toString`

() String

Inherited from Filter: `toString:161`

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`

### `_multiPass`

Filter private

Inherited from Filter: `_multiPass:79`

Another filter that is required to act as part of this filter and created and managed under the hood.

Default: null

### `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.

### `FRAG_SHADER`

String readonly

Inherited from Filter: `FRAG_SHADER:98`

Pre-processed template shader code. It will be parsed before being fed in into the shader compiler. This should be based upon StageGL.SHADER_FRAGMENT_BODY_REGULAR

### `usesContext`

Boolean

Inherited from Filter: `usesContext:71`

A flag stating that this filter uses a context draw mode and cannot be batched into imageData processing.

Default: false

### `VTX_SHADER`

String readonly

Inherited from Filter: `VTX_SHADER:88`

Pre-processed template shader code. It will be parsed before being fed in into the shader compiler. This should be based upon StageGL.SHADER_VERTEX_BODY_REGULAR