将数据存储为纹理以在顶点着色器中用于实例几何(THREE JS / GLSL)

时间:2018-01-29 14:39:08

标签: three.js glsl textures webgl

我正在使用THREE.InstancedBufferGeometry,我希望访问Vertex Shader中的数据,编码为纹理。

我想要做的是创建一个数据纹理,每个实例有一个像素,它将存储每个实例的位置数据(然后在稍后阶段,我可以使用带有流场的模拟来更新纹理以设置动画位置)。

我正在努力从顶点着色器中的纹理访问数据。

const INSTANCES_COUNT = 5000;

// FOR EVERY INSTANCE, GIVE IT A RANDOM X, Y, Z  OFFSET, AND SAVE IT IN DATA TEXTURE
const data = new Uint8Array(4 * INSTANCES_COUNT);
for (let i = 0; i < INSTANCES_COUNT; i++) {
    const stride = i * 4;
    data[stride] = (Math.random() - 0.5);
    data[stride + 1] = (Math.random() - 0.5);
    data[stride + 2] = (Math.random() - 0.5);
    data[stride + 3] = 0.0;
}

const offsetTexture = new THREE.DataTexture( data, INSTANCES, 1, THREE.RGBAFormat, THREE.FloatType );
offsetTexture.minFilter = THREE.NearestFilter;
offsetTexture.magFilter = THREE.NearestFilter;
offsetTexture.generateMipmaps = false;
offsetTexture.needsUpdate = true;

// CREATE MY INSTANCED GEOMETRY
const geometry = new THREE.InstancedBufferGeometry();
geometry.maxInstancedCount = INSTANCES_COUNT;
geometry.addAttribute( 'position', new THREE.Float32BufferAttribute([5, -5, 0, -5, 5, 0, 0, 0, 5], 3 )); // SIMPLE TRIANGLE


const vertexShader = `
    precision highp float;

    uniform vec3 color;
    uniform sampler2D offsetTexture;

    uniform mat4 modelViewMatrix;
    uniform mat4 projectionMatrix;

    attribute vec3 position;

    varying vec3 vPosition;
    varying vec3 vColor;


    void main(){
        vPosition = position;

        vec4 orientation = vec4(.0, .0, .0, .0);
        vec3 vcV = cross( orientation.xyz, vPosition );
        vPosition = vcV * ( 2.0 * orientation.w ) + ( cross( orientation.xyz, vcV ) * 2.0 + vPosition );

        vec2 uv = position.xy;
        vec4 data = texture2D( offsetTexture, uv );
        vec3 particlePosition = data.xyz * 1000.0;

        gl_Position = projectionMatrix * modelViewMatrix * vec4( vPosition + particlePosition, 1.0 );
    }
`;

const fragmentShader = `
    precision highp float;
    varying vec3 vColor;

    void main() {
        gl_FragColor = vec4(vColor, 1.0);
    }
`;

const uniforms = {
    size: { value: 1.0 },
    color: {
        type: 'c',
        value: new THREE.Color(0x3db230),
    },
    offsetTexture: {
        type: 't',
        value: offsetTexture,
    },
};

// CREATE MY MATERIAL
const material = new THREE.RawShaderMaterial({
    uniforms,
    vertexShader,
    fragmentShader,
    side: THREE.DoubleSide,
    transparent: false,
});

scene.add(new THREE.Mesh(geometry, material));

目前似乎在顶点着色器中无法访问图像中的数据(例如,如果我只是将vUv设置为vec2(1.0,0.0),并更改偏移位置,则没有任何变化),而且我也不确定如何确保实例可以在纹理中引用正确的纹理元素。

所以,我的两个问题是: 1)如何正确设置数据图像纹理,并在顶点着色器中访问该数据 2)如何正确引用存储每个特定实例的数据的纹素(例如,实例1000应使用vec2(1000,1)等

此外,我是否必须规范化数据(0.0-1.0,或0-255,或-1 - +1)

由于

1 个答案:

答案 0 :(得分:0)

您需要为每个实例的纹理计算某种索引。 意思是,您需要一个将由每个实例共享的属性。

如果你的三角形是

[a,b,c]

你的索引应该是

[0,0,0] 

假设你有1024个实例和1024x1 px纹理。

attribute float aIndex;

vec2 myIndex = ((aIndex + 0.5)/1024.,1.);

vec4 myRes = texture2D( mySampler, myIndex);