Add existing to tracked

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

@@ -0,0 +1,11 @@
+in vec4 position;
+
+out vec4 positionEC;
+
+void main()
+{
+    positionEC = czm_modelView * position;
+    gl_Position = czm_projection * positionEC;
+
+    czm_vertexLogDepth();
+}