'Ghost' outline appearing beside polygon

[javier-lopez-1s]

What happened?

If you render a CZML polygon and you zoom in along its boundary, at a small enough camera distance you can see a faint line appearing beside the polygon. I believe the line has the same shape as the polygon but different size, because if I render a narrow triangle then I can see two faint lines converging to a point. Also, this faint line seems to be rendered at a different height than the polygon because when you pan the map the line doesn't move as much as the polygon, so you can make the line appear both outside and inside the polygon.
Reproducible in Chrome and Firefox, but not in Edge.

Reproduction steps

1. Render a CZML polygon with no outline.
2. Zoom in along the polygon boundary.

Sandcastle example

https://sandcastle.cesium.com/#c=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

Environment

Browser: Chrome 134, Firefox 136
CesiumJS Version: @cesium/engine 13.1.0, but also current version in Sandcastle.
Operating System: Windows 11

[javier-lopez-1s]

Edge doesn't reproduce the problem with the sandcastle provided, but it does with a narrow triangle, where two faint lines can be seen.

[ggetz]

Thanks for the report @javier-lopez-1s! Would you mind visiting webglreport.com and taking a screenshot of your results?

We've seen some driver-related issues with ground primitives in the past and that info may help determine the source of the issue.

[javier-lopez-1s]

Thanks for your answer, @ggetz! Please find the WebGL reports below.

[javier-lopez-1s]

Hi @ggetz. I have created a better sandcastle displaying a CZML polygon where it can be seen that the faint silhouette has the same shape as the polygon (but smaller size). It appears in the center of the screen and hardly moves from that position when the map is panned. Also, it only appears when the polygon is rendered as a Ground Primitive (and disappears if its height is set and thus is rendered as a regular primitive).

https://sandcastle.cesium.com/#c=lVVtb9s2EP4rgj85gCuLEkWJXhosc4ohQLIWS4YBq/uBlmiHCCUaJOXWHfzfd3qhI9P5MkOwqHvuuTvdc6QKVRsbFErp0gQfg6+rOoDfhyTMMpzSfBbgKIxRhOJkFkSzEUooOaGEpudojnFOBxTFMTlHKUrS1KEowj4axafI2A+cYZr0YJTH2CsqTxGOBzSFLH5ReZYNKIYSLkrGQ9oooQh5aJIhFxkniHooImR43Sj248aOh/I885qYJgnuUEQzyOChMbzOgOY49dqU9X3tudAMD40QThxKMg8lFJF4QEnuBSZRmtEBpFnbzzM0JpETAKW5VzJJEkpPqB8YJ67BMcEXYHqKi+Mk89HO1Aub+kNBUkwcN80uwLwVswMhq582S7CjEurPBMkpcmmzLPFbQWHGHEou1IOXJG5Scewrj3DmuDlNffUSFLu8MLO+8glGrmZKqI9igvIT6tf8zqZe1d9+WdWruuhPgp+VdOfAvz1PlItgNSlV0VS8tqvJEK5mFW+B5T+PD8HvXFXcasHNIvii5GGr6pPjnmsjVN36ojAazMfZRQbNS5/qcvzJy2DXYwFcptEbVvCT2wAtXLzWYoSFpGZkC4KCaau2mu1eRHHHt5q35fZn38x5HU+rilmuBZNnIYySolwqqfSZGWK/YwsCvV2zRfA1TrvJai9YfpuNnY6jp7f1sV/0huO5RnvBv3MNKtX8e7DkRjRV2N/+FuWW2+lqUnSPS1VbJmquoVN9ZWtm+AM7cKh0IN5XbMv1oTOGG62qL1rtRcn1rTnUxbQvY/B9FpI/st0T13tR8IHp/DvyX1pO3SsMpHUjZPmoykbyDp3cGsOtmT/zH7bR3Mz/YHBn8hOI83J/v5pcDU3o7/2/KXjNk7vPtTwsAqsb3ltfD7e2Umb3wjXMyYZJcwJ+Uz8Gy6o+XkH3+q6FXST4B/Hrpx1M0RJmTLO2VVpJCR68ZmvJH5R6hRZ3Ef4/GzplR2ynXMkse1KNLjh0rRKGg48TEDbe3QkOpWLltN2Mo9Lf2CZkZTm9iDbyLbq6wo08PKtpJ33JjRU1s91WHJJ+klLsjBJlWPINa6QNx1vkWS3hCTxZPYg6HriR4/RDFEYEPgxwotAUPqVZStsDL4TPEIFzEkd5TjKKwUbS6OpN1hKE7wuKwnTQaTKbXBt7kPzGDdKvotopbYMGxicM55ZXOwl708zXTfHKoWZjWmLrej0fU69LsYfD5eM7+yEoJDMGkE0j5ZP4CYfJzfUc/C+orRKi3n6GY0yyQ+v2gm4eemMYhtdzeHyfaZWSa6a9yP8B