Addressing issue Rajawali#1784:

- adding throws IllegalStateException to Matrix4.setToNormal() as it depends on Matrix4.inverse()
- putting call to setToNormal() in Material.setModelMatrix() in try/catch block, thus enabling continued rendering of degenerate/zero-scale Object3Ds (which have singular model matrices)

rajawali/src/main/java/org/rajawali3d/materials/Material.java

@@ -1073,7 +1073,12 @@ public void setModelMatrix(Matrix4 modelMatrix) {
         mModelMatrix = modelMatrix;//.getFloatValues();
         mVertexShader.setModelMatrix(mModelMatrix);
 
-        mNormalMatrix.setAll(modelMatrix).setToNormalMatrix();
+        mNormalMatrix.setAll(modelMatrix);
+        try {
+            mNormalMatrix.setToNormalMatrix();
+        } catch (IllegalStateException exception) {
+            // modelMatrix is degenerate (zero scale)
+        }
         float[] matrix = mNormalMatrix.getFloatValues();
 
         mNormalFloats[0] = matrix[0];

rajawali/src/main/java/org/rajawali3d/math/Matrix4.java

@@ -339,7 +339,7 @@ public double determinant() {
      *
      * @return A reference to this {@link Matrix4} to facilitate chaining.
      *
-     * @throws IllegalStateException if this matrix is singular and cannot be in
+     * @throws IllegalStateException if this matrix is singular and cannot be inverted
      */
     @NonNull
     public Matrix4 inverse() throws IllegalStateException {
@@ -717,9 +717,11 @@ public Matrix4 lerp(@NonNull Matrix4 matrix, double t) {
      * Removes the translational component, inverts and transposes the matrix.
      *
      * @return A reference to this {@link Matrix4} to facilitate chaining.
+     *
+     * @throws IllegalStateException if this matrix is singular and cannot be inverted
      */
     @NonNull
-    public Matrix4 setToNormalMatrix() {
+    public Matrix4 setToNormalMatrix() throws IllegalStateException {
         m[M03] = 0;
         m[M13] = 0;
         m[M23] = 0;