[Visualpython-users] [patch] Level-of-detail fix

[Robert X. <nne...@gm...>]

When I was using VPython, I noticed that the level-of-detail for objects
sometimes appears incorrect (in my application, I move the camera around, so
this may exacerbate the problem). See
http://img512.imageshack.us/img512/1860/ringlod.png for an example of this
issue: the only difference between the two images is the direction that the
camera is facing (the ring is positioned to be exactly in front of the
camera).

I found out that the implementation of frame::world_frame_transform()
appears to be incorrect somehow, and so this is a patch which corrects it.

===================================================================
--- frame.cpp
+++ frame.cpp
@@ -174,44 +174,9 @@
 tmatrix
 frame::world_frame_transform() const
 {
-    // Performs a reorientation transform.
-    // ret = translation o reorientation
-    // ret = ireorientation o itranslation.
+    // This was previously incorrect, and has now been corrected by using
the inverse of frame_world_transform.
     tmatrix ret;
-
-    // A unit vector along the z_axis.
-    vector z_axis = vector(0,0,1);
-    if (std::fabs(axis.dot(up) / std::sqrt( up.mag2() * axis.mag2())) >
0.98) {
-        if (std::fabs(axis.norm().dot( vector(-1,0,0))) > 0.98)
-            z_axis = axis.cross( vector(0,0,1)).norm();
-        else
-            z_axis = axis.cross( vector(-1,0,0)).norm();
-    }
-    else {
-        z_axis = axis.cross( up).norm();
-    }
-
-    vector y_axis = z_axis.cross(axis).norm();
-    vector x_axis = axis.norm();
-    /*
-    x_axis /= scale.x;
-    y_axis /= scale.y;
-    z_axis /= scale.z;
-    */
-
-    ret(0,0) = x_axis.x;
-    ret(0,1) = x_axis.y;
-    ret(0,2) = x_axis.z;
-    ret(0,3) = (pos * x_axis).sum();
-    ret(1,0) = y_axis.x;
-    ret(1,1) = y_axis.y;
-    ret(1,2) = y_axis.z;
-    ret(1,3) = (pos * y_axis).sum();
-    ret(2,0) = z_axis.x;
-    ret(2,1) = z_axis.y;
-    ret(2,2) = z_axis.z;
-    ret(2,3) = (pos * z_axis).sum();
-
+    inverse(ret, frame_world_transform(1.0));
     return ret;
 }

Now, the ring appears correct at all scale levels, and appears to be
correctly degraded when zoomed out.

Robert