Painting JavaFX 3D surface with crosshair

Hypersurface3D.java

public void updatePaintMesh() {
    //in case the data grid dimensions have changed 
    //make the painting image the same dimension as the data grid for easy math
    diffusePaintImage = new WritableImage(
        Double.valueOf(xWidth*surfScale).intValue(), 
        Double.valueOf(zWidth*surfScale).intValue()
    );
    //if this is the first time ....
    if(null == paintTriangleMesh) {
            paintTriangleMesh = new TriangleMesh();
            paintMeshView = new MeshView(paintTriangleMesh);
            paintMeshView.setMouseTransparent(true);
            paintMeshView.setMesh(paintTriangleMesh);
            paintMeshView.setCullFace(CullFace.NONE);
            paintPhong = new PhongMaterial(Color.WHITE, 
                diffusePaintImage, null, null, null);
            paintPhong.setSpecularColor(Color.WHITE);
            paintPhong.setDiffuseColor(Color.WHITE);
            paintMeshView.setMaterial(paintPhong);            
            sceneRoot.getChildren().add(paintMeshView);
            //debug trick to change the color of the whole apint surface
            surfPlot.addEventHandler(MouseEvent.MOUSE_CLICKED, e -> {
                if(e.getClickCount() > 1 && e.isControlDown()) {
                    Color color = new Color(rando.nextDouble(), rando.nextDouble(), rando.nextDouble(), 1.0);
                    paintSingleColor(color);    
                }
            });
        }

        TriangleMesh surfMesh = (TriangleMesh)surfPlot.getMesh();
//        paintTriangleMesh.getTexCoords().setAll(surfMesh.getTexCoords());
        paintTriangleMesh.getPoints().setAll(surfMesh.getPoints());
//        paintTriangleMesh.getFaces().setAll(surfMesh.getFaces());
        
        paintTriangleMesh.getFaces().clear();
        paintTriangleMesh.getTexCoords().clear();
        final int texCoordSize = 2;

        Float pSkip = 1.0f;
        int pskip = pSkip.intValue();        
        int subDivX = (int) diffusePaintImage.getWidth() / pskip;
        int subDivZ = (int) diffusePaintImage.getHeight() / pskip;        
        int numDivX = subDivX + 1;
        int numVerts = (subDivZ + 1) * numDivX;   
        float currZ, currX;        
        float texCoords[] = new float[numVerts * texCoordSize];  
        int faceCount = subDivX * subDivZ * 2;
        final int faceSize = 6; //should always be 6 for a triangle mesh
        int faces[] = new int[faceCount * faceSize];
        int index, p00,p01,p10,p11,tc00,tc01,tc10,tc11;
        
        //Map the 2D data grid to UV coordinates and paint a single color to test
        for (int z = 0; z < subDivZ; z++) {
            currZ = (float) z / subDivZ;
            for (int x = 0; x < subDivX; x++) {
                currX = (float) x / subDivX;
                index = z * numDivX * texCoordSize + (x * texCoordSize);
                texCoords[index] = currX;
                texCoords[index + 1] = currZ;                
                
                // Create faces
                p00 = z * numDivX + x;
                p01 = p00 + 1;
                p10 = p00 + numDivX;
                p11 = p10 + 1;
                tc00 = z * numDivX + x;
                tc01 = tc00 + 1;
                tc10 = tc00 + numDivX;
                tc11 = tc10 + 1;

                index = (z * subDivX * faceSize + (x * faceSize)) * 2;
                faces[index + 0] = p00;
                faces[index + 1] = tc00;
                faces[index + 2] = p10;
                faces[index + 3] = tc10;
                faces[index + 4] = p11;
                faces[index + 5] = tc11;

                index += faceSize;
                faces[index + 0] = p11;
                faces[index + 1] = tc11;
                faces[index + 2] = p01;
                faces[index + 3] = tc01;
                faces[index + 4] = p00;
                faces[index + 5] = tc00; 
                diffusePaintImage.getPixelWriter().setColor(x, z, Color.TRANSPARENT);
            }
        }
        paintTriangleMesh.getTexCoords().setAll(texCoords);
        paintTriangleMesh.getFaces().setAll(faces);        
        //force update of the material (is this actually necessary?)
        paintPhong.setDiffuseMap(diffusePaintImage);
        paintMeshView.setTranslateZ(-1);
        paintMeshView.setTranslateX(-(xWidth*surfScale)/2.0);
        paintMeshView.setTranslateZ(-(zWidth*surfScale)/2.0);
    }
    public void paintSingleColor(Color color) {
        //Map the 2D data grid to UV coordinates and paint a single color to test
        for (int z = 0; z < diffusePaintImage.getHeight(); z++) {
            for (int x = 0; x < diffusePaintImage.getWidth(); x++) {
                diffusePaintImage.getPixelWriter().setColor(x, z, color);
            }
        }        
    }
    public void illuminateCrosshair(Point3D center) {
        if(null == diffusePaintImage)
            return;
        int x = (int) center.getX();
        int z = (int) center.getZ(); //Image Y is projected into  Z
        
        PixelWriter pw = diffusePaintImage.getPixelWriter();
        for(int i=0; i<diffusePaintImage.getWidth();i++)
            pw.setColor(i, z, Color.WHITE);
        for(int i=0; i<diffusePaintImage.getHeight();i++)
            pw.setColor(x, i, Color.WHITE);
    }