Feature: Add BackdropBlurFilter (#446)

examples/src/DemoApplication.mjs

@@ -71,6 +71,7 @@ export default class DemoApplication extends PIXI.Application
             height: this.initHeight,
             autoStart: false,
             preference,
+            useBackBuffer: true,
         });
     }
 

examples/src/filters/backdropBlur.mjs

@@ -0,0 +1,11 @@
+export default function ()
+{
+    this.addFilter('BackdropBlurFilter', {
+        fishOnly: true,
+        oncreate(folder)
+        {
+            folder.add(this, 'blur', 0, 100);
+            folder.add(this, 'quality', 1, 10);
+        },
+    });
+}

examples/src/filters/index.mjs

@@ -4,6 +4,7 @@ export { default as adjustment } from './adjustment.mjs';
 export { default as advancedBloom } from './advanced-bloom.mjs';
 export { default as alpha } from './alpha.mjs';
 export { default as ascii } from './ascii.mjs';
+export { default as backdropBlur } from './backdropBlur.mjs';
 export { default as bevel } from './bevel.mjs';
 export { default as bloom } from './bloom.mjs';
 export { default as blur } from './blur.mjs';

src/backdrop-blur/BackdropBlurFilter.ts

@@ -0,0 +1,93 @@
+import {
+    BlurFilter,
+    BlurFilterOptions,
+    Filter,
+    FilterSystem,
+    GlProgram,
+    GpuProgram,
+    RenderSurface,
+    Texture,
+    TexturePool,
+} from 'pixi.js';
+import { vertex, wgslVertex } from '../defaults';
+import fragment from './backdrop-blur-blend.frag';
+import wgslFragment from './backdrop-blur-blend.wgsl';
+
+export type BackdropBlurFilterOptions = BlurFilterOptions;
+
+/**
+ * The BackdropBlurFilter applies a Gaussian blur to everything behind an object, and then draws the object on top of it.
+ *
+ * @class
+ * @extends BlurFilter
+ * @see {@link https://www.npmjs.com/package/pixi-filters|pixi-filters}
+ */
+export class BackdropBlurFilter extends BlurFilter
+{
+    private _blendPass: Filter;
+
+    /**
+     * @param options - The options of the blur filter.
+     * @param options.strength - The strength of the blur filter.
+     * @param options.quality - The quality of the blur filter.
+     * @param options.kernelSize - The kernelSize of the blur filter.Options: 5, 7, 9, 11, 13, 15.
+     */
+    constructor(options?: BackdropBlurFilterOptions)
+    {
+        super(options);
+
+        this.blendRequired = true;
+        this.padding = 0;
+
+        this._blendPass = new Filter({
+            gpuProgram: GpuProgram.from({
+                vertex: {
+                    source: wgslVertex,
+                    entryPoint: 'mainVertex',
+                },
+                fragment: {
+                    source: wgslFragment,
+                    entryPoint: 'mainFragment',
+                },
+            }),
+            glProgram: GlProgram.from({
+                vertex,
+                fragment,
+                name: 'drop-shadow-filter',
+            }),
+            resources: {
+                uBackground: Texture.EMPTY,
+            },
+        });
+    }
+
+    /**
+     * Override existing apply method in `Filter`
+     * @override
+     * @ignore
+     */
+    public apply(
+        filterManager: FilterSystem,
+        input: Texture,
+        output: RenderSurface,
+        clearMode: boolean
+    ): void
+    {
+        // @ts-expect-error - this should probably not be grabbed from a private property
+        const backTexture = filterManager._activeFilterData.backTexture;
+
+        const blurredBackground = TexturePool.getSameSizeTexture(input);
+
+        super.apply(filterManager, backTexture, blurredBackground, true);
+
+        this._blendPass.resources.uBackground = blurredBackground.source;
+        this._blendPass.apply(filterManager, input, output, clearMode);
+
+        TexturePool.returnTexture(blurredBackground);
+    }
+
+    protected updatePadding(): void
+    {
+        this.padding = 0;
+    }
+}

src/backdrop-blur/backdrop-blur-blend.frag

@@ -0,0 +1,19 @@
+precision highp float;
+in vec2 vTextureCoord;
+out vec4 finalColor;
+
+uniform sampler2D uTexture;
+uniform sampler2D uBackground;
+
+void main(void){
+    vec4 front = texture(uTexture, vTextureCoord);
+    vec4 back = texture(uBackground, vTextureCoord);
+
+    if (front.a == 0.0) {
+        discard;
+    }
+
+    vec3 color = mix(back.rgb, front.rgb / front.a, front.a);
+
+    finalColor = vec4(color, 1.0);
+}

src/backdrop-blur/backdrop-blur-blend.wgsl

@@ -0,0 +1,20 @@
+@group(0) @binding(1) var uTexture: texture_2d<f32>; 
+@group(0) @binding(2) var uSampler: sampler;
+@group(1) @binding(0) var uBackground: texture_2d<f32>; 
+
+@fragment
+fn mainFragment(
+    @builtin(position) position: vec4<f32>,
+    @location(0) uv : vec2<f32>
+) -> @location(0) vec4<f32> {
+    var front: vec4<f32> = textureSample(uTexture, uSampler, uv);
+    var back: vec4<f32> = textureSample(uBackground, uSampler, uv);
+
+    if (front.a == 0.0) {
+        discard;
+    }
+
+    var color: vec3<f32> = mix(back.rgb, front.rgb / front.a, front.a);
+
+    return vec4<f32>(color, 1.0);
+}

src/backdrop-blur/index.ts

@@ -0,0 +1 @@
+export * from './BackdropBlurFilter';

src/index.ts

@@ -1,6 +1,7 @@
 export * from './adjustment';
 export * from './advanced-bloom';
 export * from './ascii';
+export * from './backdrop-blur';
 export * from './bevel';
 export * from './bloom';
 export * from './bulge-pinch';