bloomPass.js

import { fullscreenQuadReglBase, loadText, makePassFBO, makePass, requireShaderString } from "./utils.js";

// The bloom pass is basically an added high-pass blur.
// The blur approximation is the sum of a pyramid of downscaled, blurred textures.

const pyramidHeight = 5;

// A pyramid is just an array of FBOs, where each FBO is half the width
// and half the height of the FBO below it.
const makePyramid = (regl, height, halfFloat) =>
	Array(height)
		.fill()
		.map((_) => makePassFBO(regl, halfFloat));

const resizePyramid = (pyramid, vw, vh, scale) =>
	pyramid.forEach((fbo, index) => fbo.resize(Math.floor((vw * scale) / 2 ** index), Math.floor((vh * scale) / 2 ** index)));

export default ({ regl, config }, inputs) => {
	const { bloomStrength, bloomSize, highPassThreshold } = config;
	const enabled = bloomSize > 0 && bloomStrength > 0;

	// If there's no bloom to apply, return a no-op pass with an empty bloom texture
	if (!enabled) {
		return makePass({
			primary: inputs.primary,
			bloom: makePassFBO(regl),
		});
	}

	// Build three pyramids of FBOs, one for each step in the process
	const highPassPyramid = makePyramid(regl, pyramidHeight, config.useHalfFloat);
	const hBlurPyramid = makePyramid(regl, pyramidHeight, config.useHalfFloat);
	const vBlurPyramid = makePyramid(regl, pyramidHeight, config.useHalfFloat);
	const output = makePassFBO(regl, config.useHalfFloat);

	// The high pass restricts the blur to bright things in our input texture.
	const highPassFrag = loadText("shaders/glsl/bloomPass.highPass.frag.glsl");
	const blurFrag = loadText("shaders/glsl/bloomPass.blur.frag.glsl");
	const combineFrag = loadText("shaders/glsl/bloomPass.combine.frag.glsl");

	let highPass;
	let blur;
	let combine;
	const programsReady = Promise.all([highPassFrag.loaded, blurFrag.loaded, combineFrag.loaded]).then(() => {
		highPass = regl({
			...fullscreenQuadReglBase,
			frag: requireShaderString("bloomPass.highPass.frag", () => highPassFrag.text()),
			uniforms: {
				highPassThreshold,
				tex: regl.prop("tex"),
			},
			framebuffer: regl.prop("fbo"),
		});
		blur = regl({
			...fullscreenQuadReglBase,
			frag: requireShaderString("bloomPass.blur.frag", () => blurFrag.text()),
			uniforms: {
				tex: regl.prop("tex"),
				direction: regl.prop("direction"),
				height: regl.context("viewportWidth"),
				width: regl.context("viewportHeight"),
			},
			framebuffer: regl.prop("fbo"),
		});
		combine = regl({
			...fullscreenQuadReglBase,
			frag: requireShaderString("bloomPass.combine.frag", () => combineFrag.text()),
			uniforms: {
				bloomStrength,
				...Object.fromEntries(vBlurPyramid.map((fbo, index) => [`pyr_${index}`, fbo])),
			},
			framebuffer: output,
		});
	});

	return makePass(
		{
			primary: inputs.primary,
			bloom: output,
		},
		programsReady,
		(w, h) => {
			// The blur pyramids can be lower resolution than the screen.
			resizePyramid(highPassPyramid, w, h, bloomSize);
			resizePyramid(hBlurPyramid, w, h, bloomSize);
			resizePyramid(vBlurPyramid, w, h, bloomSize);
			output.resize(w, h);
		},
		(shouldRender) => {
			if (!shouldRender) {
				return;
			}

			for (let i = 0; i < pyramidHeight; i++) {
				const highPassFBO = highPassPyramid[i];
				const hBlurFBO = hBlurPyramid[i];
				const vBlurFBO = vBlurPyramid[i];
				highPass({ fbo: highPassFBO, tex: i === 0 ? inputs.primary : highPassPyramid[i - 1] });
				blur({ fbo: hBlurFBO, tex: highPassFBO, direction: [1, 0] });
				blur({ fbo: vBlurFBO, tex: hBlurFBO, direction: [0, 1] });
			}

			combine({});
		},
	);
};