[SOLVED] Fix normals

sc3 · October 15, 2021, 11:15pm

Hi,
The cube in the blue circle has its shadow and lighted sides correct.
The objects in the red circle have their shadow and lighted sides inverted,
according to the direction of the light source.
How can I fix the normals so that the shadows are on the correct side ?

Blue circle: geometry created through com.jme3.scene.shape.Box
Rec circle: geometries created through GitHub - FennelFetish/jBMesh

pspeed · October 15, 2021, 11:50pm

If they are indeed consistently exactly backwards then that’s weird that the library produces them that way.

To fix this in code the steps would be:

grab the mesh
get its Type.Normal VertexBuffer
grab the FloatBuffer from it
multiply all values in the FloatBuffer by -1 and set them back.
send the VertexBuffer back to the mesh… (at least I think there is a way you need to tell the Mesh that the buffer has changed… you can look at some of the mesh subclass’s updateXXX() style methods to see).

…or maybe someone else has that handy.

sgold · October 16, 2021, 4:22am

A utility to flip normals is Included in the MyMesh utility class in the Heart library.

Source code is here:

github.com

stephengold/Heart/blob/6a0e44051edcb1d3137207279d7cabd2e0101b3c/HeartLibrary/src/main/java/jme3utilities/MyMesh.java#L882

    
      
           * @deprecated use MyBuffer.readIndex()

           */

          @Deprecated

          public static int readIndex(Buffer buffer) {

              Validate.nonNull(buffer, "buffer");

              int result = MyBuffer.readIndex(buffer);

              return result;

          }

          

          /**

           * Reverse the normals of a Mesh. Apply this method (for instance) after

           * reversing the winding order of a triangle mesh.

           *

           * @param mesh the Mesh to modify (not null)

           */

          public static void reverseNormals(Mesh mesh) {

              FloatBuffer buffer = mesh.getFloatBuffer(VertexBuffer.Type.Normal);

              if (buffer != null) {

                  MyBuffer.scale(buffer, 0, buffer.limit(), scaleReverse);

              }

If the normals are flipped, you may also need to reverse the winding order, since incorrect winding order might be the cause. MyMesh also has a utility for that.

pspeed · October 16, 2021, 8:20am

Winding order looks right or the objects would be rendered inside out.

sc3 · October 16, 2021, 10:34am

Heart solved my problems

Reversing the normals solved the issue depicted in the screenshot, light and shadow went to the right side.
And reversing the winding solved another problem that I hadn’t mentioned, namely that the objects didn’t ‘receive’ shadow.

Thank you @sgold and @pspeed for your work and time !!