Sphere Impostor on ThreeJS - three.js

Question

I am developing a sphere impostor shader on GLSL with ThreeJS. My algorithm is based on the publication from Sigg et al. named "GPU-Based Ray-Casting of Quadratic Surfaces".
When using a classic geometry approach, you need dozens or even hundreds triangles to represent each sphere. It may cause memory overload if you need to show thousands of spheres. The sphere impostor allows you to store only positions and radius on the geometry to show a sphere, giving much more performance than the previous technique.
For now, I succeeded to develop the shader, even by using ThreeJS shader chunks to ensure a full ThreeJS compatibility. You can find a demo page here. However, there is a last thing not working on this implementation.
When moving the objects on the scene, it seems that the object using the sphere impostor is delayed compared to a normal mesh. You can also notice that some times, the spheres are "cut" like on this picture.
This second bug makes me think that the sprite is nicely placed into the scene by the vertex shader but the fragment shader is computing wrong coordinates. I suspect two pieces of code where the problem could be :
Two varyings provided by the vertex shader to the fragment shader that should give the same value for each pixel of a sprite. I don't know how to verify this.
varying float projMatrix11;
varying float projMatrix22;
I don't know if I'm doing well to update my shader uniforms
group.traverse(function(o) {
if (!o.material) { return; }
var u = o.material.uniforms;
if (!u) { return; }
modelViewMatrixInverse.getInverse(
o.modelViewMatrix
);
if (u.projectionMatrixInverse) {
u.projectionMatrixInverse.value = projectionMatrixInverse;
}
if (u.projectionMatrixTranspose) {
u.projectionMatrixTranspose.value = projectionMatrixTranspose;
}
if (u.modelViewMatrixInverse) {
u.modelViewMatrixInverse.value = modelViewMatrixInverse;
}
if (u.viewport) {
u.viewport.value = viewport;
}
});
I wasn't able to debug the problem and hope someone knowing better ThreeJS than I can give me some clues about it.
I really hope we can solve this problem, so we may be able to propose this feature to the whole community of ThreeJS ;)
Note : I delayed the calls of requestAnimationFrame for you to facilitate debugging
EDIT : After digging more, the problem may come from how I'm updating custom uniforms. One of it uses the modelViewMatrix to get it's inverse. But the modelViewMatrix is updated only during the render call of the WebGLRenderer, so the frame delay may come from there. How can I update a uniform which is depending to other uniforms and keep them synchronized on ThreeJS ?

Answer 1

Answer found alone, I will explain it here if someone encounters the same trouble.
The problem is that I was updating modelViewMatrixInverse uniform by using the modelViewMatrix provided by ThreeJS. This uniform is only updated during the call of render() method of the WebGLRenderer and my modelViewMatrixInverse was one frame late at each render call. That's why my custom shader was everytime one frame late than ThreeJS native shaders.