How to update the position of an object in the scene after matrix movement in the vertex shader?

Questions
1

I created a cube mesh using THREE.BoxBufferGeometry , and used matrix transformation to implement mesh rotation and scaling in the vertex shader. These matrices are all used as uniform variables. After I made a displacement change to the mesh, the mesh successfully implemented the displacement in the scene, but then I used mesh.position to get the position of the mesh in javascript and found that its value has not changed. mesh.position is not updated.

            material = new THREE.ShaderMaterial( {
                vertexShader: document.getElementById( 'volumeVertex' ).textContent,
                fragmentShader: document.getElementById( 'volumeFragment' ).textContent,
                side: THREE.DoubleSide,

                uniforms: {
                            rotateMatrix:{value:rotateMatrix.elements},
                            scaleMatrix:{value:scaleMatrix.elements},
                            translateMatrix:{value:translateMatrix.elements}
                           }
                });

            boxGeometry = new THREE.BoxBufferGeometry(2, 2, 2);
            boxGeometry.doubleSided = true;
            mesh = new THREE.Mesh( boxGeometry, material );
            scene.add( mesh );

vertex shader code:

<script id="volumeVertex" type="x-shader/x-vertex">
        uniform mat4 rotateMatrix;
        uniform mat4 translateMatrix;
        uniform mat4 scaleMatrix;

        void main()
        {
            vec4 newPos =  translateMatrix * rotateMatrix *scaleMatrix * vec4(position,1.0);
            gl_Position = projectionMatrix *  modelViewMatrix * newPos;

        }

Change the position of the mesh through a matrix:

          var translateMatrix = new THREE.Matrix4();
          translateMatrix.makeTranslation(5,5,5);
          var preTransMatrix = new THREE.Matrix4();
          preTransMatrix.elements = mesh.material.uniforms.translateMatrix.value;
          translateMatrix.multiply(preTransMatrix);
          mesh.material.uniforms.translateMatrix.value = translateMatrix.elements;

the mesh can move to (5,5,5) ,but when I console.log(mesh.position.x,mesh.position.y,mesh.position.z) ,the result is the initial position (0,0,0) .How to update the mesh.postion after matrix movement ?

2

You know THREE does that entirely for you? Perorming this on GPU doesn’t feedback at all to JS, you only transform the vertices on GPU here.

If you want the world position of a mesh which is a child of a hierarchy, you can use:

myVector3.setFromMatrixPosition(mesh.matrixWorld);