Cesium3DTileStyle - alpha value not respected for loaded tiles

[TJPovey]

CesiumJS versions
Issue present in CesiumJS version 1.105 & 1.105.1. (No issues in cesiumjs version 1.92) Only tested in versions: 1.105, 1.105.1, 1.92

Expected behaviour:

When changing the style of a Cesium3DTileset using either of the following:

    tileset.style = new Cesium.Cesium3DTileStyle({
      color: 'rgba(255,255,255,0.5)'
    });

    tileset.style = new Cesium.Cesium3DTileStyle({
      color: 'color("white", 0.5)'
    });

I expect that all existing / newly loaded tiles to respect the assigned alpha value. Regardless of if the style has been added before or after the initial render of a Cesium3DTileset.

Actual behaviour
When changing the alpha value of a Cesium3DTileset, existing tiles use the old alpha value. Newly loaded tiles use the new alpha value.

The alpha value is respected if the style has been added prior to the model being added to the scene. If the alpha value is changed after this, the issue occurs:

Sandcastle example:

By showing the tiles content volume, we can see that older tiles aren't affected by the alpha value change.

Sandcastle

Browser:
Tested on Chrome (Version 113.0.5672.127) & Edge (Version 113.0.1774.50)

Operating System:
Windows 10 Enterprise - version 21H2

[TJPovey]

More easily seen when showing content volumes:

[TJPovey]

Ok, I've tested on all versions between 1.92 and 1.105.1, it looks like the bug was introduced in version 1.97. These were the major changes in this version.
Maybe texture caching is the culprit?

[j9liu]

The culprit is this block of code:

/**
 * @private
 */
Model.prototype.applyColorAndShow = function (style) {
  const previousColor = this._color;
  const hasColorStyle = defined(style) && defined(style.color);
  const hasShowStyle = defined(style) && defined(style.show);

  this._color = hasColorStyle
    ? style.color.evaluateColor(undefined, this._color)
    : Color.clone(Color.WHITE, this._color);
  this._show = hasShowStyle ? style.show.evaluate(undefined) : true;

  if (isColorAlphaDirty(previousColor, this._color)) {
    this.resetDrawCommands();
  }
};

previousColor is storing this._color, and when this._color is later being changed by the style, this also changes previousColor. The correct solution would be to use a scratch Color variable for previousColor. Then, use Color.clone to copy the color into previousColor, before potentially changing it via the style.

[TJPovey]

perfect thanks @j9liu