Improve appearance of the material editor preview

- Use lower camera FOV to show more of the sphere/box, while still
  fully displaying the meshes in question.

editor/plugins/material_editor_plugin.cpp

@@ -155,7 +155,9 @@ MaterialEditor::MaterialEditor() {
 
 	camera = memnew(Camera3D);
 	camera->set_transform(Transform3D(Basis(), Vector3(0, 0, 3)));
-	camera->set_perspective(45, 0.1, 10);
+	// Use low field of view so the sphere/box is fully encompassed within the preview,
+	// without much distortion.
+	camera->set_perspective(20, 0.1, 10);
 	camera->make_current();
 	viewport->add_child(camera);
 
@@ -177,8 +179,8 @@ MaterialEditor::MaterialEditor() {
 	Transform3D box_xform;
 	box_xform.basis.rotate(Vector3(1, 0, 0), Math::deg2rad(25.0));
 	box_xform.basis = box_xform.basis * Basis().rotated(Vector3(0, 1, 0), Math::deg2rad(-25.0));
-	box_xform.basis.scale(Vector3(0.8, 0.8, 0.8));
-	box_xform.origin.y = 0.2;
+	box_xform.basis.scale(Vector3(0.7, 0.7, 0.7));
+	box_xform.origin.y = 0.05;
 	box_instance->set_transform(box_xform);
 
 	sphere_mesh.instantiate();