Color randomization of Polygon Style affected by Alpha in CesiumVectorStyle

Cesium for Unreal
1

Hi, Dear Cesium Team,

I am using Unreal 5.6 with Cesium for Unreal V2.21.0.

1.If the CesiumGeoJsonDocumentRasterOverlay loads a LineString GeoJSON file, the color randomization of Line Style is not affected by Alpha, which is correct, I think.

(1)Set the Line Color to full red value and full Alpha value, and the result is as follows.

c5e66025c8391deedf251e0d428a0e73
c5e66025c8391deedf251e0d428a0e73460×275 3.89 KB

532aa4eb570a83e3481315e939637dbd
532aa4eb570a83e3481315e939637dbd983×688 152 KB

(2)Set the Line Color to full red value and half Alpha value, and the result is as follows

fd2805468c745c5aeb1fc5819d56e164
fd2805468c745c5aeb1fc5819d56e164477×276 4.06 KB

b51349e7a90cbd9f14542e21060b1ee4
b51349e7a90cbd9f14542e21060b1ee4924×714 145 KB

2.However, if the CesiumGeoJsonDocumentRasterOverlay loads a MultiPolygon GeoJSON file , the color randomization of Polygon Style is affected by Alpha, which is not correct.

(1)Set the Fill Color to full red value and full Alpha value, and the result is as follows.

0bf3f344bafa9681085d1a94fc6fd606
0bf3f344bafa9681085d1a94fc6fd606463×254 4.11 KB

58a3f0ef86b8f161e2907a389ab5939c
58a3f0ef86b8f161e2907a389ab5939c1010×515 119 KB

(2)Set the Fill Color to full red value and half Alpha value, and the result is as follows.

67eb822162e2d51ab4f835e1bb1556db
67eb822162e2d51ab4f835e1bb1556db470×252 4 KB

b5b104648c90a44b35f60eaa803b6374
b5b104648c90a44b35f60eaa803b63741139×535 109 KB

You can see that the value of Alpha has affected the random color, and the output result is not translucent.

3.Additionally, in the documentation,Cesium for Unreal: Source/CesiumRuntime/Public/CesiumVectorStyle.h File Reference ,the description of the example is incorrect.

It is likely that the byte order is mixed up, and the correct description should be as follows:

For example, If the color was 0x007700ff (only 0x77 in the green component), the resulting randomized value could be 0x004100ff, or 0x007600ff, but never 0x00aa00ff.

3

Hi @pjiang9, sorry for the delayed response! This post fell through the cracks.

@azrogers, could you chime in here about whether this is a bug or intended behavior?

4

@pjiang9 You are definitely right that the documentation is incorrect! However, I am unable to reproduce your issue with a MultiPolygon dataset using the same color values. The transparency works correctly, and the alpha value does not affect the random color. This is with a bing maps raster overlay set up as Overlay0, and a GeoJSON raster overlay set up as Overlay1. If you are still experiencing this issue, could you share a sample project that I can use to reproduce it? Thank you!

5

Thank you, janine. Thank you,azrogers.

The project is attached.

The code is all in the Level Blueprint.

I also found that if I limit the Object Type to the Feature Collection level, the result seems to be as expected. But this is somewhat illogical. Logically speaking, with 16 Features, each Feature should be able to have a different random Polygon color set independently.

Right now I’m not sure if it’s a bug.

PolygonRandomTest.zip (27.8 MB)

6

It turns out the source of the issue is that the GeoJsonDocumentRasterOverlay was incorrectly including both the FeatureCollection and the polygons it contained within the list of geometry to be rendered. This means it would render the feature collection, which in turn would render all the contained polygons using the FeatureCollection’s style, and would then rendere each polygon individually, which would use the Polygon’s style. This is why you got correct results setting it on the Feature Collection level. I’ve included the fix for this in this pull request to improve GeoJSON rasterizing in general, which I’m hoping will make it into the release at the end of the month!

7

That makes sense. Thank you! Looking forward to the new GeoJsonDocumentRasterOverlay.