Adding new attribute for instancing

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It is now possible to set attributes on standard material (in the next release, 1.66 probably). This allows you to provide additional data per each instance. The method is simple - when creating a vertex buffer, instead of the default vertex format, you create your own one and then set the semantics on the material.

Here is an example of passing two pc.Vec3 vectors:

// 16 for TRS matrix and +3 for each additional vector
const data = new Float32Array(instanceCount * (16 + 6));

let index = 0;
for (let i = 0; i < instanceCount; i++) {
    matrix.setTRS(pos, pc.Quat.IDENTITY, pc.Vec3.ONE);

    // add some custom vectorA
    data[index++] = vectorA.x;
    data[index++] = vectorA.y;
    data[index++] = vectorA.z;

    // add vectorB
    data[index++] = vectorB.x;
    data[index++] = vectorB.y;
    data[index++] = vectorB.z;

    for (let m = 0; m < 16; m++) {
        buffer[bufferIndex++] = matrix.data[m];
    }
}

// create vertex format, 10-11 - our vectorA and vectorB, 12-15 - instancing data
const format = new pc.VertexFormat(device, [
    { semantic: pc.SEMANTIC_ATTR10, components: 3, type: pc.TYPE_FLOAT32 },
    { semantic: pc.SEMANTIC_ATTR11, components: 3, type: pc.TYPE_FLOAT32 },
    { semantic: pc.SEMANTIC_ATTR12, components: 4, type: pc.TYPE_FLOAT32 },
    { semantic: pc.SEMANTIC_ATTR13, components: 4, type: pc.TYPE_FLOAT32 },
    { semantic: pc.SEMANTIC_ATTR14, components: 4, type: pc.TYPE_FLOAT32 },
    { semantic: pc.SEMANTIC_ATTR15, components: 4, type: pc.TYPE_FLOAT32 },
]);            

// create vertex buffer
const vertexBuffer = new pc.VertexBuffer(device, format, instanceCount, pc.BUFFER_STATIC, data);

// add attributes on material to map semantics
standardMaterial.setAttribute('vectorA', pc.SEMANTIC_ATTR10);
standardMaterial.setAttribute('vectorB', pc.SEMANTIC_ATTR11);

// create mesh instance, using that material and provide vertex buffer for instancing
const instance = new pc.MeshInstance(mesh, material);
instance.setInstancing(vertexBuffer);

Then in your vertex chunk, e.g. transformVS

attribute vec3 vectorA, vectorB;
vec4 getPosition()
{
    vec4 something = vec4(vectorA, 1.);
}
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