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+// Original src: https://github.com/zz85/threejs-path-flow
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+const BITS = 3;
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+const TEXTURE_WIDTH = 1024;
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+const TEXTURE_HEIGHT = 4;
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+
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+import {
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+ DataTexture,
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+ RGBFormat,
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+ FloatType,
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+ RepeatWrapping,
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+ Mesh,
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+ InstancedMesh,
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+ NearestFilter,
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+ DynamicDrawUsage,
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+ Matrix4
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+} from "../../../build/three.module.js";
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+
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+/**
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+ * Make a new DataTexture to store the descriptions of the curves.
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+ *
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+ * @param { number } numberOfCurves the number of curves needed to be described by this texture.
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+ */
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+export function initSplineTexture( numberOfCurves = 1 ) {
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+
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+ const dataArray = new Float32Array( TEXTURE_WIDTH * TEXTURE_HEIGHT * numberOfCurves * BITS );
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+ const dataTexture = new DataTexture(
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+ dataArray,
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+ TEXTURE_WIDTH,
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+ TEXTURE_HEIGHT * numberOfCurves,
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+ RGBFormat,
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+ FloatType
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+ );
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+
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+ dataTexture.wrapS = RepeatWrapping;
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+ dataTexture.wrapY = RepeatWrapping;
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+ dataTexture.magFilter = NearestFilter;
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+ dataTexture.needsUpdate = true;
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+
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+ return dataTexture;
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+
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+}
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+
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+/**
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+ * Write the curve description to the data texture
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+ *
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+ * @param { DataTexture } texture The DataTexture to write to
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+ * @param { Curve } splineCurve The curve to describe
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+ * @param { number } offset Which curve slot to write to
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+ */
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+export function updateSplineTexture( texture, splineCurve, offset = 0 ) {
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+
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+ const numberOfPoints = Math.floor( TEXTURE_WIDTH * ( TEXTURE_HEIGHT / 4 ) );
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+ splineCurve.arcLengthDivisions = numberOfPoints / 2;
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+ splineCurve.updateArcLengths();
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+ const points = splineCurve.getSpacedPoints( numberOfPoints );
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+ const frenetFrames = splineCurve.computeFrenetFrames( numberOfPoints, true );
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+
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+ for ( let i = 0; i < numberOfPoints; i ++ ) {
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+
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+ const rowOffset = Math.floor( i / TEXTURE_WIDTH );
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+ const rowIndex = i % TEXTURE_WIDTH;
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+
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+ let pt = points[ i ];
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+ setTextureValue( texture, rowIndex, pt.x, pt.y, pt.z, 0 + rowOffset + ( TEXTURE_HEIGHT * offset ) );
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+ pt = frenetFrames.tangents[ i ];
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+ setTextureValue( texture, rowIndex, pt.x, pt.y, pt.z, 1 + rowOffset + ( TEXTURE_HEIGHT * offset ) );
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+ pt = frenetFrames.normals[ i ];
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+ setTextureValue( texture, rowIndex, pt.x, pt.y, pt.z, 2 + rowOffset + ( TEXTURE_HEIGHT * offset ) );
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+ pt = frenetFrames.binormals[ i ];
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+ setTextureValue( texture, rowIndex, pt.x, pt.y, pt.z, 3 + rowOffset + ( TEXTURE_HEIGHT * offset ) );
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+
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+ }
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+
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+ texture.needsUpdate = true;
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+
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+}
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+
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+
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+function setTextureValue( texture, index, x, y, z, o ) {
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+
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+ const image = texture.image;
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+ const { data } = image;
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+ const i = BITS * TEXTURE_WIDTH * o; // Row Offset
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+ data[ index * BITS + i + 0 ] = x;
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+ data[ index * BITS + i + 1 ] = y;
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+ data[ index * BITS + i + 2 ] = z;
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+
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+}
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+
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+/**
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+ * Create a new set of uniforms for describing the curve modifier
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+ *
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+ * @param { DataTexture } Texture which holds the curve description
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+ */
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+export function getUniforms( splineTexture ) {
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+
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+ const uniforms = {
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+ spineTexture: { value: splineTexture },
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+ pathOffset: { type: 'f', value: 0 }, // time of path curve
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+ pathSegment: { type: 'f', value: 1 }, // fractional length of path
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+ spineOffset: { type: 'f', value: 161 },
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+ spineLength: { type: 'f', value: 400 },
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+ flow: { type: 'i', value: 1 },
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+ };
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+ return uniforms;
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+
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+}
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+
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+export function modifyShader( material, uniforms, numberOfCurves = 1 ) {
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+
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+ if ( material.__ok ) return;
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+ material.__ok = true;
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+
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+ material.onBeforeCompile = ( shader ) => {
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+
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+ if ( shader.__modified ) return;
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+ shader.__modified = true;
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+
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+ Object.assign( shader.uniforms, uniforms );
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+
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+ const vertexShader = `
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+ uniform sampler2D spineTexture;
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+ uniform float pathOffset;
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+ uniform float pathSegment;
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+ uniform float spineOffset;
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+ uniform float spineLength;
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+ uniform int flow;
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+
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+ float textureLayers = ${TEXTURE_HEIGHT * numberOfCurves}.;
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+ float textureStacks = ${TEXTURE_HEIGHT / 4}.;
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+
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+ ${shader.vertexShader}
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+ `.replace(
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+ '#include <defaultnormal_vertex>',
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+ `
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+ vec4 worldPos = modelMatrix * vec4(position, 1.);
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+
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+ bool bend = flow > 0;
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+ float xWeight = bend ? 0. : 1.;
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+
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+ #ifdef USE_INSTANCING
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+ float pathOffsetFromInstanceMatrix = instanceMatrix[3][2];
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+ float spineLengthFromInstanceMatrix = instanceMatrix[3][0];
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+ float spinePortion = bend ? (worldPos.x + spineOffset) / spineLengthFromInstanceMatrix : 0.;
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+ float mt = (spinePortion * pathSegment + pathOffset + pathOffsetFromInstanceMatrix)*textureStacks;
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+ #else
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+ float spinePortion = bend ? (worldPos.x + spineOffset) / spineLength : 0.;
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+ float mt = (spinePortion * pathSegment + pathOffset)*textureStacks;
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+ #endif
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+
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+ mt = mod(mt, textureStacks);
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+ float rowOffset = floor(mt);
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+
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+ #ifdef USE_INSTANCING
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+ rowOffset += instanceMatrix[3][1] * ${TEXTURE_HEIGHT}.;
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+ #endif
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+
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+ vec3 spinePos = texture(spineTexture, vec2(mt, (0. + rowOffset + 0.5) / textureLayers)).xyz;
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+ vec3 a = texture(spineTexture, vec2(mt, (1. + rowOffset + 0.5) / textureLayers)).xyz;
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+ vec3 b = texture(spineTexture, vec2(mt, (2. + rowOffset + 0.5) / textureLayers)).xyz;
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+ vec3 c = texture(spineTexture, vec2(mt, (3. + rowOffset + 0.5) / textureLayers)).xyz;
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+ mat3 basis = mat3(a, b, c);
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+
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+ vec3 transformed = basis
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+ * vec3(worldPos.x * xWeight, worldPos.y * 1., worldPos.z * 1.)
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+ + spinePos;
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+
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+ vec3 transformedNormal = normalMatrix * (basis * objectNormal);
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+ `
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+ ).replace(
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+ '#include <begin_vertex>',
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+ ''
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+ ).replace(
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+ '#include <project_vertex>',
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+ `
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+ vec4 mvPosition = viewMatrix * vec4( transformed, 1.0 );
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+ // vec4 mvPosition = viewMatrix * worldPos;
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+ gl_Position = projectionMatrix * mvPosition;
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+ `
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+ );
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+
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+ shader.vertexShader = vertexShader;
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+
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+ };
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+
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+}
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+
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+/**
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+ * A helper class for making meshes bend aroudn curves
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+ */
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+export class Flow {
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+
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+ /**
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+ * @param {Mesh} mesh The mesh to clone and modify to bend around the curve
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+ * @param {number} numberOfCurves The amount of space that should preallocated for additional curves
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+ */
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+ constructor( mesh, numberOfCurves = 1 ) {
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+
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+ const obj3D = mesh.clone();
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+ const splineTexure = initSplineTexture( numberOfCurves );
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+ const uniforms = getUniforms( splineTexure );
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+ obj3D.traverse( function ( child ) {
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+
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+ if (
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+ child instanceof Mesh ||
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+ child instanceof InstancedMesh
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+ ) {
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+
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+ child.material = child.material.clone();
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+ modifyShader( child.material, uniforms, numberOfCurves );
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+
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+ }
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+
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+ } );
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+
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+ this.curveArray = new Array( numberOfCurves );
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+ this.curveLengthArray = new Array( numberOfCurves );
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+
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+ this.object3D = obj3D;
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+ this.splineTexure = splineTexure;
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+ this.uniforms = uniforms;
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+
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+ }
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+
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+ updateCurve( index, curve ) {
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+
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+ if ( index >= this.curveArray.length ) throw Error( 'Index out of range for Flow' );
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+ const curveLength = curve.getLength();
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+ this.uniforms.spineLength.value = curveLength;
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+ this.curveLengthArray[ index ] = curveLength;
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+ this.curveArray[ index ] = curve;
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+ updateSplineTexture( this.splineTexure, curve, index );
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+
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+ }
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+
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+ moveAlongCurve( amount ) {
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+
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+ this.uniforms.pathOffset.value += amount;
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+
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+ }
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+
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+}
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+const matrix = new Matrix4();
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+
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+/**
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+ * A helper class for creating instanced versions of flow, where the instances are placed on the curve.
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+ */
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+export class InstancedFlow extends Flow {
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+
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+ /**
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+ *
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+ * @param {number} count The number of instanced elements
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+ * @param {number} curveCount The number of curves to preallocate for
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+ * @param {Geometry} geometry The geometry to use for the instanced mesh
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+ * @param {Material} material The material to use for the instanced mesh
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+ */
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+ constructor( count, curveCount, geometry, material ) {
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+
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+ const mesh = new InstancedMesh(
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+ geometry,
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+ material,
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+ count
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+ );
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+ mesh.instanceMatrix.setUsage( DynamicDrawUsage );
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+ super( mesh, curveCount );
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+
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+ this.offsets = new Array( count ).fill( 0 );
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+ this.whichCurve = new Array( count ).fill( 0 );
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+
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+ }
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+
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+ /**
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+ * The extra information about which curve and curve position is stored in the translation components of the matrix for the instanced objects
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+ * This writes that information to the matrix and marks it as needing update.
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+ *
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+ * @param {number} index of the instanced element to update
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+ */
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+ writeChanges( index ) {
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+
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+ matrix.makeTranslation(
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+ this.curveLengthArray[ this.whichCurve[ index ] ],
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+ this.whichCurve[ index ],
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+ this.offsets[ index ]
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+ );
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+ this.object3D.setMatrixAt( index, matrix );
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+ this.object3D.instanceMatrix.needsUpdate = true;
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+
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+ }
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+
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+ /**
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+ * Move an individual element along the curve by a specific amount
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+ *
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+ * @param {number} index Which element to update
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+ * @param {number} offset Move by how much
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+ */
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+ moveIndividualAlongCurve( index, offset ) {
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+
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+ this.offsets[ index ] += offset;
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+ this.writeChanges( index );
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+
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+ }
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+
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+ /**
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+ * Select which curve to use for an element
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+ *
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+ * @param {number} index the index of the instanced element to update
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+ * @param {number} curveNo the index of the curve it should use
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+ */
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+ setCurve( index, curveNo ) {
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+
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+ if ( isNaN( curveNo ) ) throw Error( "curve index being set is Not a Number (NaN)" );
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+ this.whichCurve[ index ] = curveNo;
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+ this.writeChanges( index );
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+
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+ }
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+
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+}
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