partial texture update in three.js - three.js

Question

I upload a large texture to my fragment shader as a map in three.js.
This texture is a 2D canvas on which I draw random shapes.
While drawing, I just want to update the part of the texture that has changed. Updating the whole texture (up to 3000x3000 pixel) is just too slow.
However, I can not get to perform a partial update. texSubImage2D doesn't have any effect in my scene.
No errors in the console - I expect that I am missing a step but can not figure it out yet.
//
// create drawing canvas 2D and related textures
//
this._canvas = document.createElement('canvas');
this._canvas.width = maxSliceDimensionsX;
this._canvas.height = maxSliceDimensionsY;
this._canvasContext = this._canvas.getContext('2d')!;
this._canvasContext.fillStyle = 'rgba(0, 0, 0, 0)';
this._canvasContext.fillRect(0, 0, window.innerWidth, window.innerHeight);
this._texture = new Texture(this._canvas);
this._texture.magFilter = NearestFilter;
this._texture.minFilter = NearestFilter;
// const data = new Uint8Array(maxSliceDimensionsX * maxSliceDimensionsY * 4);
// this._texture2 = new THREE.DataTexture(data, maxSliceDimensionsX, maxSliceDimensionsY, THREE.RGBAFormat);
this._brushMaterial = new MeshBasicMaterial({
map: this._texture,
side: DoubleSide,
transparent: true,
});
...
// in the render loop
renderLoop() {
...
// grab random values as a test
const imageData = this._canvasContext.getImageData(100, 100, 200, 200);
const uint8Array = new Uint8Array(imageData.data.buffer);
// activate texture?
renderer.setTexture2D(this._texture, 0 );
// update subtexture
const context = renderer.getContext();
context.texSubImage2D( context.TEXTURE_2D, 0, 0, 0, 200, 200, context.RGBA, context.UNSIGNED_BYTE, uint8Array);
// updating the whole texture works as expected but is slow
// this._texture.needsUpdate = true;
// Render new scene
renderer.render(scene, this._camera);
}
Thanks,
Nicolas

Answer 1

Right after creating the texture, we must notify three that the texture needs to be uploaded to the GPU.
We just have to set it 1 time at creation time and not in the render loop.
this._texture = new Texture(this._canvas);
this._texture.magFilter = NearestFilter;
this._texture.minFilter = NearestFilter;
// MUST BE ADDED
this._texture.needsUpdate = true;