Decouple voxel coordinate conversion in shader

packages/engine/Source/Shaders/Voxels/convertUvToEllipsoid.glsl

@@ -48,15 +48,33 @@ vec2 nearestPointOnEllipse(vec2 pos, vec2 radii) {
     return v * sign(pos);
 }
 
-/**
- * Composition of convertUvToShapeSpace and convertShapeToShapeUvSpace
- */
-vec3 convertUvToShapeUvSpace(in vec3 positionUv) {
+vec3 convertUvToShapeSpace(in vec3 positionUv) {
     // Convert positionUv [0,1] to local space [-1,+1]
     vec3 positionLocal = positionUv * 2.0 - 1.0;
 
-    // Compute longitude, shifted and scaled to the range [0, 1]
-    float longitude = (atan(positionLocal.y, positionLocal.x) + czm_pi) / czm_twoPi;
+    float longitude = atan(positionLocal.y, positionLocal.x);
+
+    // Convert position to "normalized" cartesian space [-a,+a] where a = (radii + height) / (max(radii) + height).
+    // A point on the largest ellipsoid axis would be [-1,+1] and everything else would be smaller.
+    vec3 posEllipsoid = positionLocal * u_ellipsoidRadiiUv;
+
+    // Convert the 3D position to a 2D position relative to the ellipse (radii.x, radii.z)
+    // (assume radii.y == radii.x) and find the nearest point on the ellipse.
+    vec2 posEllipse = vec2(length(posEllipsoid.xy), posEllipsoid.z);
+    vec2 surfacePoint = nearestPointOnEllipse(posEllipse, u_ellipsoidRadiiUv.xz);
+
+    vec2 normal = normalize(surfacePoint * u_ellipsoidInverseRadiiSquaredUv.xz);
+    float latitude = atan(normal.y, normal.x);
+
+    float heightSign = length(posEllipse) < length(surfacePoint) ? -1.0 : 1.0;
+    float height = heightSign * length(posEllipse - surfacePoint);
+
+    return vec3(longitude, latitude, height);
+}
+
+vec3 convertShapeToShapeUvSpace(in vec3 positionShape) {
+    // Longitude: shift & scale to [0, 1]
+    float longitude = (positionShape.x + czm_pi) / czm_twoPi;
 
     // Correct the angle when max < min
     // Technically this should compare against min longitude - but it has precision problems so compare against the middle of empty space.
@@ -76,24 +94,19 @@ vec3 convertUvToShapeUvSpace(in vec3 positionUv) {
         longitude = longitude * u_ellipsoidUvToShapeUvLongitude.x + u_ellipsoidUvToShapeUvLongitude.y;
     #endif
 
-    // Convert position to "normalized" cartesian space [-a,+a] where a = (radii + height) / (max(radii) + height).
-    // A point on the largest ellipsoid axis would be [-1,+1] and everything else would be smaller.
-    vec3 posEllipsoid = positionLocal * u_ellipsoidRadiiUv;
-    // Convert the 3D position to a 2D position relative to the ellipse (radii.x, radii.z)
-    // (assume radii.y == radii.x) and find the nearest point on the ellipse.
-    vec2 posEllipse = vec2(length(posEllipsoid.xy), posEllipsoid.z);
-    vec2 surfacePoint = nearestPointOnEllipse(posEllipse, u_ellipsoidRadiiUv.xz);
-
-    // Compute latitude, shifted and scaled to the range [0, 1]
-    vec2 normal = normalize(surfacePoint * u_ellipsoidInverseRadiiSquaredUv.xz);
-    float latitude = (atan(normal.y, normal.x) + czm_piOverTwo) / czm_pi;
+    // Latitude: shift and scale to [0, 1]
+    float latitude = (positionShape.y + czm_piOverTwo) / czm_pi;
     #if defined(ELLIPSOID_HAS_SHAPE_BOUNDS_LATITUDE)
         latitude = latitude * u_ellipsoidUvToShapeUvLatitude.x + u_ellipsoidUvToShapeUvLatitude.y;
     #endif
 
-    // Compute height
-    float heightSign = length(posEllipse) < length(surfacePoint) ? -1.0 : 1.0;
-    float height = 1.0 + heightSign * length(posEllipse - surfacePoint) * u_ellipsoidInverseHeightDifferenceUv;
+    // Height: scale to the range [0, 1]
+    float height = 1.0 + positionShape.z * u_ellipsoidInverseHeightDifferenceUv;
 
     return vec3(longitude, latitude, height);
 }
+
+vec3 convertUvToShapeUvSpace(in vec3 positionUv) {
+    vec3 positionShape = convertUvToShapeSpace(positionUv);
+    return convertShapeToShapeUvSpace(positionShape);
+}