Draped polygons not rendering

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Steve McNamara Steve McNamara
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Draped polygons not rendering


I'm looking into an issue with draped polygons. I'm hoping that someone else has also seen this issue and could offer some advice.

The issue I see is that the polygons only draw when the camera altitude is high. As the map is zoomed in they start to disappear, ending with them not being drawn at all.

This issue occurs when using Mesa to render, on both Ubuntu 20.04 and Windows 10.

Software versions I'm using:
[osgEarth]  [Capabilities] Capabilities:
[osgEarth]  [Capabilities]   osgEarth Version:  3.1.0 build 100
[osgEarth]  [Capabilities]   OSG Version:       3.6.5
[osgEarth]  [Capabilities]   GDAL Version:      2.4.0
[osgEarth]  [Capabilities]   GEOS Version:      3.5.0
[osgEarth]  [Capabilities]   GPU Vendor:        VMware, Inc.
[osgEarth]  [Capabilities]   GPU Renderer:      llvmpipe (LLVM 10.0.0, 256 bits)
[osgEarth]  [Capabilities]   GL/Driver Version: 4.1 (Compatibility Profile) Mesa 20.0.8
[osgEarth]  [Capabilities]   GL Core Profile:   no

I've reproduced the problem using the osgearth_windows and the annotations.earth sample.

This screenshot shows a working draped polygon:

Draped polygon drawing correcting

Zoom in on the earth and the polygon starts to disappear:

Draped polygon not drawing

The draping issue does not occur when using hardware OpenGL. This issue appears to only occur when using Mesa.

Any advice would be appreciated.

For completeness, the earth file I'm using to reproduced the problem is:

<map name="Annotations Demo">

    <XYZImage name="osm_mapnik" cache_enabled="true">
        <cache_policy usage="read_write"/> 

        <viewpoint name="Annotation Samples"
                   lat="33" long="-118" range="500000"
                   heading="35.27" pitch="-35" />

    <Annotations name="Annotations Group B">

        <feature name="Draped Polygon">
                POLYGON((-100 47, -100 49, -95 48, -96 45, -98 42))
            <style type="text/css"> fill: #ffff007f; stroke: #ffffff; stroke-width: 2px; altitude-clamping: terrain-drape; </style>        </feature>
        <label text="Draped Polygon" lat="45" long="-98"/>