Add existing to tracked

node_modules/@cesium/engine/Source/Shaders/BufferPolygonMaterialFS.glsl

@@ -0,0 +1,13 @@
+in vec4 v_pickColor;
+in vec4 v_color;
+
+void main()
+{
+    if (v_color.a < 0.005)   // matches 0/255 and 1/255
+    {
+        discard;
+    }
+
+    out_FragColor = czm_gammaCorrect(v_color);
+    czm_writeLogDepth();
+}