fix(imagereslicemapper): be less sensitive for "snapping" to nearest …

…orthogonal axis

When using the vtkImageResliceMapper in conjunction with the ResliceCursorWidget(RWC), there was a
case when the RCW lines were displayed partly being the slice when the slice plane was being snapped
to the nearest orthogonal axis.

Sources/Rendering/OpenGL/ImageResliceMapper/index.js

@@ -1131,14 +1131,18 @@ function vtkOpenGLImageResliceMapper(publicAPI, model) {
     shaders.Fragment = FSSource;
   };
 
+  /**
+   * Returns true if the normal is almost axis aligned.
+   * Has a side effect to normalize the vector.
+   */
   function isVectorAxisAligned(n) {
     vtkMath.normalize(n);
     const tmpN = [0, 0, 0];
     for (let i = 0; i < 3; ++i) {
       vec3.zero(tmpN);
       tmpN[i] = 1.0;
       const dotP = vtkMath.dot(n, tmpN);
-      if (dotP < -0.999 || dotP > 0.999) {
+      if (dotP < -0.999999 || dotP > 0.999999) {
         return [true, i];
       }
     }