Class Filter

A filter is a special shader that applies post-processing effects to an input texture and writes into an output render-target.

Example of the PIXI.BlurFilter BlurFilter.

Usage

Filters can be applied to any DisplayObject or Container. PixiJS' FilterSystem renders the container into temporary Framebuffer, then filter renders it to the screen. Multiple filters can be added to the filters array property and stacked on each other.

import { Container, Filter } from 'pixi.js';
const filter = new Filter(myShaderVert, myShaderFrag, { myUniform: 0.5 });
const container = new Container();
container.filters = [filter];
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Previous Version Differences

In PixiJS v3, a filter was always applied to whole screen.

In PixiJS v4, a filter can be applied only part of the screen. Developers had to create a set of uniforms to deal with coordinates.

In PixiJS v5 combines both approaches. Developers can use normal coordinates of v3 and then allow filter to use partial Framebuffers, bringing those extra uniforms into account.

Also be aware that we have changed default vertex shader, please consult Wiki.

Frames

The following table summarizes the coordinate spaces used in the filtering pipeline:

Coordinate Space	Description
Texture Coordinates	The texture (or UV) coordinates in the input base-texture's space. These are normalized into the (0,1) range along both axes.
World Space	A point in the same space as the world bounds of any display-object (i.e. in the scene graph's space).
Physical Pixels	This is base-texture's space with the origin on the top-left. You can calculate these by multiplying the texture coordinates by the dimensions of the texture.

Built-in Uniforms

PixiJS viewport uses screen (CSS) coordinates, (0, 0, renderer.screen.width, renderer.screen.height), and projectionMatrix uniform maps it to the gl viewport.

uSampler

The most important uniform is the input texture that container was rendered into. Important note: as with all Framebuffers in PixiJS, both input and output are premultiplied by alpha.

By default, input normalized coordinates are passed to fragment shader with vTextureCoord. Use it to sample the input.

import { Filter } from 'pixi.js';
const fragment = `
varying vec2 vTextureCoord;
uniform sampler2D uSampler;
void main(void)
{
   gl_FragColor = texture2D(uSampler, vTextureCoord);
}
`;

const myFilter = new Filter(null, fragment);
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This filter is just one uniform less than PIXI.AlphaFilter AlphaFilter.

outputFrame

The outputFrame holds the rectangle where filter is applied in screen (CSS) coordinates. It's the same as renderer.screen for a fullscreen filter. Only a part of outputFrame.zw size of temporary Framebuffer is used, (0, 0, outputFrame.width, outputFrame.height),

Filters uses this quad to normalized (0-1) space, its passed into aVertexPosition attribute. To calculate vertex position in screen space using normalized (0-1) space:

vec4 filterVertexPosition( void )
{
    vec2 position = aVertexPosition * max(outputFrame.zw, vec2(0.)) + outputFrame.xy;
    return vec4((projectionMatrix * vec3(position, 1.0)).xy, 0.0, 1.0);
}
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inputSize

Temporary framebuffer is different, it can be either the size of screen, either power-of-two. The inputSize.xy are size of temporary framebuffer that holds input. The inputSize.zw is inverted, it's a shortcut to evade division inside the shader.

Set inputSize.xy = outputFrame.zw for a fullscreen filter.

To calculate input normalized coordinate, you have to map it to filter normalized space. Multiply by outputFrame.zw to get input coordinate. Divide by inputSize.xy to get input normalized coordinate.

vec2 filterTextureCoord( void )
{
    return aVertexPosition * (outputFrame.zw * inputSize.zw); // same as /inputSize.xy
}
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resolution

The resolution is the ratio of screen (CSS) pixels to real pixels.

inputPixel

inputPixel.xy is the size of framebuffer in real pixels, same as inputSize.xy * resolution inputPixel.zw is inverted inputPixel.xy.

It's handy for filters that use neighbour pixels, like PIXI.FXAAFilter FXAAFilter.

inputClamp

If you try to get info from outside of used part of Framebuffer - you'll get undefined behaviour. For displacements, coordinates has to be clamped.

The inputClamp.xy is left-top pixel center, you may ignore it, because we use left-top part of Framebuffer inputClamp.zw is bottom-right pixel center.

vec4 color = texture2D(uSampler, clamp(modifiedTextureCoord, inputClamp.xy, inputClamp.zw));
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Or:

vec4 color = texture2D(uSampler, min(modifigedTextureCoord, inputClamp.zw));
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Additional Information

Complete documentation on Filter usage is located in the Wiki.

Since PixiJS only had a handful of built-in filters, additional filters can be downloaded here from the PixiJS Filters repository.

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