JavaFX 3d Sphere - texture mapping saving proportions?

Question

I am trying to have a JavaFX 3D Sphere, textured with a texture of the earth. The texture is this one (from Wikipedia, an equirectangular projection):

The sphere is rendered as follows:

You can clearly see that, at the poles, the texture is not preserving the proportions anymore. I found a bug files on the openJDK system, which I think is related to this behaviour: https://bugs.java.com/bugdatabase/view_bug.do?bug_id=8092112

Sadly, in 7 years nobody made the change that the person filing the bug requested. Do you know if there is an alternative way to properly render an equirectangular sphere projection on a JavaFX 3D Sphere?

Just for reference, the code that I using is:

    Sphere earthSphere = new Sphere(EARTH_RADIUS, 256);
    PhongMaterial material = new PhongMaterial();
    material.setDiffuseMap(new Image(Main.class.getResourceAsStream("/images/earth2.jpg")));
    earthSphere.setMaterial(material);

Perhaps patch the [Sphere class](https://github.com/openjdk/jfx/blob/master/modules/javafx.graphics/src/main/java/javafx/scene/shape/Sphere.java#L336) in your installation with the suggested fix from the bug report. You could instead modify the input texture so that the default JavaFX sphere texture mapper will work for your texture, but I don't know how you would do that. — jewelsea, Oct 10 '22 at 14:40
If anybody is wondering what the earth should look like, you can see it at [nasa](https://solarsystem.nasa.gov/resources/2393/earth-3d-model/). — jewelsea, Oct 10 '22 at 14:44

score 2 · Accepted Answer · answered Oct 12 '22 at 08:19

At the end I implement it myself using a mesh, for the purposes I needed for. Here is the code, in case you are interested (it will end up in a GitHub project anyway):

public static Group createEarthSphere() {
    // Use triangular mesh
    int latLevels = 90;
    int lonLevels = 180;

    TriangleMesh mesh = new TriangleMesh(VertexFormat.POINT_NORMAL_TEXCOORD);
    double radius = EARTH_RADIUS;

    double latIncAngle = (Math.PI/latLevels);
    double lonIncAngle = (Math.PI * 2)/lonLevels;
    double textLatIncr = 1.0/latLevels;
    double textLonIncr = 1.0/lonLevels;

    int currentPointOffset = 0;
    int currentNormalOffset = 0;
    int currentTextOffset = 0;
    for(int i = 0; i < latLevels; ++i) {
        for(int j = 0; j < lonLevels; ++j) {
            // The point list is: top left - bottom left - bottom right - top right
            // The faces-normal points are: (0,0) (1,1) (2,2) (0,3) (2,4) (3,5)
            Point3D tp1 = new Point3D(0,radius * Math.cos(Math.PI - (i * latIncAngle)), radius * Math.sin(Math.PI - (i * latIncAngle)));
            Point3D tp2 = new Point3D(0,radius * Math.cos(Math.PI - (i * latIncAngle + latIncAngle)), radius * Math.sin(Math.PI - (i * latIncAngle + latIncAngle)));
            Point3D topLeft = new Rotate(Math.toDegrees(j * lonIncAngle), new Point3D(0, 1, 0)).transform(tp1);
            Point3D bottomLeft =  new Rotate(Math.toDegrees(j * lonIncAngle), new Point3D(0, 1, 0)).transform(tp2);
            Point3D bottomRight = new Rotate(Math.toDegrees(j * lonIncAngle + lonIncAngle), new Point3D(0, 1, 0)).transform(tp2);
            Point3D topRight = new Rotate(Math.toDegrees(j * lonIncAngle + lonIncAngle), new Point3D(0, 1, 0)).transform(tp1);

            // Compute normals
            Point3D topLeftNormal_1 = computeNormal(topLeft, bottomLeft, bottomRight); // 0
            Point3D bottomLeftNormal_1 = computeNormal(bottomLeft, bottomRight, topLeft); // 1
            Point3D bottomRightNormal_1 = computeNormal(bottomRight, topLeft, bottomLeft); // 2
            Point3D topLeftNormal_2 = computeNormal(topLeft, bottomRight, topRight); // 3
            Point3D bottomRightNormal_2 = computeNormal(bottomRight, topRight, topLeft); // 4
            Point3D topRightNormal_2 = computeNormal(topRight, topLeft, bottomRight); // 5

            // Add points
            mesh.getPoints().addAll((float) topLeft.getX(), (float) topLeft.getY(), (float) topLeft.getZ()); // 0
            mesh.getPoints().addAll((float) bottomLeft.getX(), (float) bottomLeft.getY(), (float) bottomLeft.getZ()); // 1
            mesh.getPoints().addAll((float) bottomRight.getX(), (float) bottomRight.getY(), (float) bottomRight.getZ()); // 2
            mesh.getPoints().addAll((float) topRight.getX(), (float) topRight.getY(), (float) topRight.getZ()); // 3

            // Add normals
            mesh.getNormals().addAll((float) topLeftNormal_1.getX(), (float) topLeftNormal_1.getY(), (float) topLeftNormal_1.getZ()); // 0
            mesh.getNormals().addAll((float) bottomLeftNormal_1.getX(), (float) bottomLeftNormal_1.getY(), (float) bottomLeftNormal_1.getZ()); // 1
            mesh.getNormals().addAll((float) bottomRightNormal_1.getX(), (float) bottomRightNormal_1.getY(), (float) bottomRightNormal_1.getZ()); // 2
            mesh.getNormals().addAll((float) topLeftNormal_2.getX(), (float) topLeftNormal_2.getY(), (float) topLeftNormal_2.getZ()); // 3
            mesh.getNormals().addAll((float) bottomRightNormal_2.getX(), (float) bottomRightNormal_2.getY(), (float) bottomRightNormal_2.getZ()); // 4
            mesh.getNormals().addAll((float) topRightNormal_2.getX(), (float) topRightNormal_2.getY(), (float) topRightNormal_2.getZ()); // 5

            // Add texture
            float[] p0t = { (float) (i * textLatIncr), 1.0f - (float) (j * textLonIncr) };
            float[] p1t = { (float) (i * textLatIncr + textLatIncr), 1.0f - (float) (j * textLonIncr) };
            float[] p2t = { (float) (i * textLatIncr + textLatIncr), 1.0f - (float) (j * textLonIncr + textLonIncr) };
            float[] p3t = { (float) (i * textLatIncr), 1.0f - (float) (j * textLonIncr + textLonIncr) };

            mesh.getTexCoords().addAll(
                    p0t[1], p0t[0],
                    p1t[1], p1t[0],
                    p2t[1], p2t[0],
                    p3t[1], p3t[0]
            );

            // Add faces
            mesh.getFaces().addAll(
                    currentPointOffset + 0, currentNormalOffset + 0, currentTextOffset + 0,
                    currentPointOffset + 2, currentNormalOffset + 2, currentTextOffset + 2,
                    currentPointOffset + 1, currentNormalOffset + 1, currentTextOffset + 1,
                    currentPointOffset + 0, currentNormalOffset + 3, currentTextOffset + 0,
                    currentPointOffset + 3, currentNormalOffset + 5, currentTextOffset + 3,
                    currentPointOffset + 2, currentNormalOffset + 4, currentTextOffset + 2

            );

            currentPointOffset += 4;
            currentNormalOffset += 6;
            currentTextOffset += 4;
        }
    }

    MeshView meshView = new MeshView(mesh);
    meshView.setCullFace(CullFace.BACK);
    PhongMaterial material = new PhongMaterial();
    material.setDiffuseMap(new Image(Main.class.getResourceAsStream("/images/earth.jpg")));
    meshView.setMaterial(material);
    return new Group(meshView);
}

private static Point3D computeNormal(Point3D p1, Point3D p2, Point3D p3) {
    return (p3.subtract(p1).normalize()).crossProduct(p2.subtract(p1).normalize()).normalize();
}

The result is:

Now everything is exactly where it should be, and lat/lon are correctly matching the texture.

JavaFX 3d Sphere - texture mapping saving proportions?

1 Answers1