fleeting-garden/src/pipelines/diffusion/diffusion-pipeline.ts

import { appConfig } from '../../config';
import {
  createCachedFloat32BufferWrite,
  writeFloat32BufferIfChanged,
} from '../../utils/graphics/cached-buffer-write';
import { setUpFullScreenQuad } from '../../utils/graphics/full-screen-quad';
import { smartCompile } from '../../utils/graphics/smart-compile';
import { CommonState } from '../common-state/common-state';
import shader from './diffuse.wgsl?raw';
import { DiffusionSettings } from './diffusion-settings';

const MIN_DIFFUSION_RATE = appConfig.pipelines.diffusion.minDiffusionRate;

type DiffusionUniformSettings = Pick<
  DiffusionSettings,
  'diffusionRateTrails' | 'decayRateTrails' | 'diffusionRateBrush' | 'decayRateBrush'
>;

export const getSafeInverseDiffusionRate = (diffusionRate: number): number =>
  1 /
  (Number.isFinite(diffusionRate) && diffusionRate > MIN_DIFFUSION_RATE
    ? diffusionRate
    : MIN_DIFFUSION_RATE);

export const setDiffusionUniformValues = (
  target: Float32Array,
  {
    diffusionRateTrails,
    decayRateTrails,
    diffusionRateBrush,
    decayRateBrush,
  }: DiffusionUniformSettings
): void => {
  target[0] = getSafeInverseDiffusionRate(diffusionRateTrails);
  target[1] = decayRateTrails / 1000;
  target[2] = getSafeInverseDiffusionRate(diffusionRateBrush);
  target[3] = decayRateBrush / 1000;
};

export class DiffusionPipeline {
  private static readonly UNIFORM_COUNT = 4;

  private readonly bindGroupLayout: GPUBindGroupLayout;
  private readonly pipeline: GPURenderPipeline;
  private readonly uniforms: GPUBuffer;
  private readonly uniformValues = new Float32Array(DiffusionPipeline.UNIFORM_COUNT);
  private readonly uniformCache = createCachedFloat32BufferWrite(
    DiffusionPipeline.UNIFORM_COUNT
  );
  private readonly vertexBuffer: GPUBuffer;

  private readonly bindGroupsByInput = new WeakMap<GPUTextureView, GPUBindGroup>();

  public constructor(
    private readonly device: GPUDevice,
    private readonly commonState: CommonState
  ) {
    this.bindGroupLayout = device.createBindGroupLayout(
      DiffusionPipeline.bindGroupLayout
    );

    const { buffer, vertex } = setUpFullScreenQuad(device);
    this.vertexBuffer = buffer;

    this.pipeline = device.createRenderPipeline({
      layout: device.createPipelineLayout({
        bindGroupLayouts: [commonState.bindGroupLayout, this.bindGroupLayout],
      }),
      vertex,
      fragment: {
        module: smartCompile(device, CommonState.shaderCode, shader),
        entryPoint: 'fragment',
        targets: [
          {
            format: 'rgba16float',
          },
        ],
      },
      primitive: {
        topology: 'triangle-strip',
      },
    });

    this.uniforms = this.device.createBuffer({
      size: DiffusionPipeline.UNIFORM_COUNT * Float32Array.BYTES_PER_ELEMENT,
      usage: GPUBufferUsage.UNIFORM | GPUBufferUsage.COPY_DST,
    });
  }

  public setParameters({
    diffusionRateTrails,
    decayRateTrails,
    diffusionRateBrush,
    decayRateBrush,
  }: DiffusionSettings) {
    setDiffusionUniformValues(this.uniformValues, {
      diffusionRateTrails,
      decayRateTrails,
      diffusionRateBrush,
      decayRateBrush,
    });
    writeFloat32BufferIfChanged(
      this.device,
      this.uniforms,
      this.uniformValues,
      this.uniformCache
    );
  }

  public execute(
    commandEncoder: GPUCommandEncoder,
    trailMapIn: GPUTextureView,
    trailMapOut: GPUTextureView
  ) {
    const bindGroup = this.getBindGroup(trailMapIn);

    const renderPassDescriptor: GPURenderPassDescriptor = {
      colorAttachments: [
        {
          view: trailMapOut,
          clearValue: { r: 0, g: 0, b: 0, a: 0 },
          loadOp: 'clear',
          storeOp: 'store',
        },
      ],
    };

    const passEncoder = commandEncoder.beginRenderPass(renderPassDescriptor);
    passEncoder.setPipeline(this.pipeline);
    passEncoder.setVertexBuffer(0, this.vertexBuffer);
    this.commonState.execute(passEncoder);
    passEncoder.setBindGroup(1, bindGroup);
    passEncoder.draw(4, 1);
    passEncoder.end();
  }

  private getBindGroup(trailMapIn: GPUTextureView): GPUBindGroup {
    const cached = this.bindGroupsByInput.get(trailMapIn);
    if (cached) {
      return cached;
    }

    const bindGroup = this.device.createBindGroup({
      layout: this.bindGroupLayout,
      entries: [
        {
          binding: 0,
          resource: {
            buffer: this.uniforms,
          },
        },
        {
          binding: 2,
          resource: trailMapIn,
        },
      ],
    });

    this.bindGroupsByInput.set(trailMapIn, bindGroup);
    return bindGroup;
  }

  public destroy() {
    this.vertexBuffer.destroy();
    this.uniforms.destroy();
  }

  private static get bindGroupLayout(): GPUBindGroupLayoutDescriptor {
    return {
      entries: [
        {
          binding: 0,
          visibility: GPUShaderStage.FRAGMENT,
          buffer: {
            type: 'uniform',
          },
        },
        {
          binding: 2,
          visibility: GPUShaderStage.FRAGMENT,
          texture: {
            sampleType: 'float',
          },
        },
      ],
    };
  }
}