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Class FragmentFilter

The FragmentFilter class is the base class for all filter effects in Starling. All filters must extend this class. You can attach them to any display object through the filter property.

A fragment filter works in the following way:

  1. The object to be filtered is rendered into a texture.
  2. That texture is passed to the process method.
  3. This method processes the texture using a FilterEffect subclass that processes the input via fragment and vertex shaders to achieve a certain effect.
  4. If the filter requires several passes, the process method may execute the effect several times, or even make use of other filters in the process.
  5. In the end, a quad with the output texture is added to the batch renderer. In the next frame, if the object hasn't changed, the filter is drawn directly from the render cache.
  6. Alternatively, the last pass may be drawn directly to the back buffer. That saves one draw call, but means that the object may not be drawn from the render cache in the next frame. Starling makes an educated guess if that makes sense, but you can also force it to do so via the alwaysDrawToBackBuffer property.

All of this is set up by the basic FragmentFilter class. Concrete subclasses just need to override the protected method createEffect and (optionally) process. Multi-pass filters must also override numPasses.

Typically, any properties on the filter are just forwarded to an effect instance, which is then used automatically by process to render the filter pass. For a simple example on how to write a single-pass filter, look at the implementation of the ColorMatrixFilter; for a composite filter (i.e. a filter that combines several others), look at the GlowFilter.

Beware that a filter instance may only be used on one object at a time!

Animated filters

The process method of a filter is only called when it's necessary, i.e. when the filter properties or the target display object changes. This means that you cannot rely on the method to be called on a regular basis, as needed when creating an animated filter class. Instead, you can do so by listening for an ENTER_FRAME-event. It is dispatched on the filter once every frame, as long as the filter is assigned to a display object that is connected to the stage.

Caching

Per default, whenever the target display object is changed in any way (i.e. the render cache fails), the filter is reprocessed. However, you can manually cache the filter output via the method of the same name: this will let the filter redraw the current output texture, even if the target object changes later on. That's especially useful if you add a filter to an object that changes only rarely, e.g. a TextField or an Image. Keep in mind, though, that you have to call cache() again in order for any changes to show up.

@see starling.rendering.FilterEffect

Hierarchy

Index

Constructors

constructor

Properties

alwaysDrawToBackBuffer

alwaysDrawToBackBuffer: boolean

Indicates if the last filter pass is always drawn directly to the back buffer.

Per default, the filter tries to automatically render in a smart way: objects that are currently moving are rendered to the back buffer, objects that are static are rendered into a texture first, which allows the filter to be drawn directly from the render cache in the next frame (in case the object remains static).

However, this fails when filters are added to an object that does not support the render cache, or to a container with such a child (e.g. a Sprite3D object or a masked display object). In such a case, enable this property for maximum performance.

@default false

antiAliasing

antiAliasing: number

The anti-aliasing level. This is only used for rendering the target object into a texture, not for the filter passes. 0 - none, 4 - maximum. @default 0

isCached

isCached: boolean

Indicates if the filter is cached (via the cache method).

Protected maintainResolutionAcrossPasses

maintainResolutionAcrossPasses: boolean

Indicates if the filter requires all passes to be processed with the exact same resolution.

Some filters must use the same resolution for input and output; e.g. the blur filter is very sensitive to changes of pixel / texel sizes. When the filter is used as part of a filter chain, or if its last pass is drawn directly to the back buffer, such a filter produces artifacts. In that case, the filter author must set this property to true.

@default false

padding

padding: Padding

Padding can extend the size of the filter texture in all directions. That's useful when the filter "grows" the bounds of the object in any direction.

resolution

resolution: number

The resolution of the filter texture. "1" means stage resolution, "0.5" half the stage resolution. A lower resolution saves memory and execution time, but results in a lower output quality. Values greater than 1 are allowed; such values might make sense for a cached filter when it is scaled up. @default 1

textureFormat

textureFormat: string

The format of the filter texture. @default BGRA

textureSmoothing

textureSmoothing: string

The smoothing mode of the filter texture. @default bilinear

Methods

Protected addEventListener

  • addEventListener(type: string, listener: Function): void

cache

  • cache(): void
  • Caches the filter output into a texture.

    An uncached filter is rendered every frame (except if it can be rendered from the global render cache, which happens if the target object does not change its appearance or location relative to the stage). A cached filter is only rendered once; the output stays unchanged until you call cache again or change the filter settings.

    Beware: you cannot cache filters on 3D objects; if the object the filter is attached to is a Sprite3D or has a Sprite3D as (grand-) parent, the request will be silently ignored. However, you can cache a 2D object that has 3D children!

    Returns void

clearCache

  • clearCache(): void

dispatchEvent

  • dispatchEvent(event: Event): void
  • Dispatches an event to all objects that have registered listeners for its type. If an event with enabled 'bubble' property is dispatched to a display object, it will travel up along the line of parents, until it either hits the root object or someone stops its propagation manually.

    Parameters

    Returns void

dispatchEventWith

  • dispatchEventWith(type: string, bubbles?: boolean, data?: any): void

dispose

  • dispose(): void

Protected get_alwaysDrawToBackBuffer

  • get_alwaysDrawToBackBuffer(): boolean

Protected get_antiAliasing

  • get_antiAliasing(): number

Protected get_isCached

  • get_isCached(): boolean

Protected get_maintainResolutionAcrossPasses

  • get_maintainResolutionAcrossPasses(): boolean

Protected get_padding

Protected get_resolution

  • get_resolution(): number

Protected get_textureFormat

  • get_textureFormat(): string

Protected get_textureSmoothing

  • get_textureSmoothing(): string

hasEventListener

  • hasEventListener(type: string, listener?: any): boolean

process

  • Does the actual filter processing. This method will be called with up to four input textures and must return a new texture (acquired from the helper) that contains the filtered output. To to do this, it configures the FilterEffect (provided via createEffect) and calls its render method.

    In a standard filter, only input0 will contain a texture; that's the object the filter was applied to, rendered into an appropriately sized texture. However, filters may also accept multiple textures; that's useful when you need to combine the output of several filters into one. For example, the DropShadowFilter uses a BlurFilter to create the shadow and then feeds both input and shadow texture into a CompositeFilter.

    Never create or dispose any textures manually within this method; instead, get new textures from the provided helper object, and pass them to the helper when you do not need them any longer. Ownership of both input textures and returned texture lies at the caller; only temporary textures should be put into the helper.

    Parameters

    Returns Texture

Protected removeEventListener

  • removeEventListener(type: string, listener: Function): void

removeEventListeners

  • removeEventListeners(type?: string): void

render

  • Renders the filtered target object. Most users will never have to call this manually; it's executed automatically in the rendering process of the filtered display object.

    Parameters

    Returns void

Protected set_alwaysDrawToBackBuffer

  • set_alwaysDrawToBackBuffer(value: boolean): boolean

Protected set_antiAliasing

  • set_antiAliasing(value: number): number

Protected set_maintainResolutionAcrossPasses

  • set_maintainResolutionAcrossPasses(value: boolean): boolean

Protected set_padding

Protected set_resolution

  • set_resolution(value: number): number

Protected set_textureFormat

  • set_textureFormat(value: string): string

Protected set_textureSmoothing

  • set_textureSmoothing(value: string): string

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