Shadows z-fighting, glPolygonOffset

sean_lilley · June 16, 2020, 7:33pm

To check if polygon offset is supported you can add console.log(viewer.scene.shadowMap._polygonOffsetSupported); or step into the code here:

github.com

CesiumGS/cesium/blob/638c6ebffe86a17637acc8dc5c223f404131f993/Source/Scene/ShadowMap.js#L132-L145


// In IE11 and Edge polygon offset is not functional.
// TODO : Also disabled for instances of Firefox and Chrome running ANGLE that do not support depth textures.
// Re-enable once https://github.com/CesiumGS/cesium/issues/4560 is resolved.
var polygonOffsetSupported = true;
if (
  FeatureDetection.isInternetExplorer() ||
  FeatureDetection.isEdge() ||
  ((FeatureDetection.isChrome() || FeatureDetection.isFirefox()) &&
    FeatureDetection.isWindows() &&
    !context.depthTexture)
) {
  polygonOffsetSupported = false;
}
this._polygonOffsetSupported = polygonOffsetSupported;

We also apply normal offset bias, which helps, but there are still shadow artifacts. It looks like your model does have normals and can use this technique. You can try tweaking some of the values here and see if it helps:

github.com

CesiumGS/cesium/blob/638c6ebffe86a17637acc8dc5c223f404131f993/Source/Scene/ShadowMap.js#L158-L167


this._primitiveBias = {
  polygonOffset: polygonOffsetSupported,
  polygonOffsetFactor: 1.1,
  polygonOffsetUnits: 4.0,
  normalOffset: this._normalOffset,
  normalOffsetScale: 0.1,
  normalShading: true,
  normalShadingSmooth: 0.05,
  depthBias: 0.00002,
};

What device are you running on? Some mobile devices have less depth buffer precision. We’ve seen issues like https://github.com/CesiumGS/cesium/issues/7176 and https://github.com/CesiumGS/cesium/issues/4752