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<DIV><FONT face=Arial>Hi,</FONT></DIV>

<DIV><FONT face=Arial></FONT>&nbsp;</DIV>

<DIV><FONT face=Arial>Below is the source code of the VTK. I do 

not&nbsp;understand the code:&nbsp;<STRONG>&nbsp; vtkRenderWindow *renWin = 

(vtkRenderWindow *)win.&nbsp; </STRONG>Because it will cause error when 

<STRONG>win-&gt;MakeCUrrent()</STRONG> is called. Hope your help!</FONT></DIV>

<DIV><FONT face=Arial></FONT>&nbsp;</DIV>

<DIV><FONT><FONT face=Arial>void vtkActor::ReleaseGraphicsResources(vtkWindow 

*win)<BR>{<BR><STRONG>&nbsp; vtkRenderWindow *renWin = (vtkRenderWindow 

*)win;</STRONG></FONT></FONT></DIV>

<DIV><FONT face=Arial></FONT>&nbsp;</DIV>

<DIV><FONT face=Arial>&nbsp; // pass this information onto the mapper<BR>&nbsp; 

if (this-&gt;Mapper)<BR>&nbsp;&nbsp;&nbsp; {<BR></FONT><FONT 

face=Arial><STRONG>&nbsp;&nbsp;&nbsp; 

this-&gt;Mapper-&gt;ReleaseGraphicsResources(renWin);<BR></STRONG>&nbsp;&nbsp;&nbsp; 

}</FONT></DIV>

<DIV><FONT face=Arial></FONT>&nbsp;</DIV>

<DIV><FONT face=Arial>&nbsp; // pass this information onto the texture<BR>&nbsp; 

if (this-&gt;Texture)<BR>&nbsp;&nbsp;&nbsp; {<BR>&nbsp;&nbsp;&nbsp; 

this-&gt;Texture-&gt;ReleaseGraphicsResources(renWin);<BR>&nbsp;&nbsp;&nbsp; 

}<BR>}<BR></FONT></DIV>

<DIV><FONT face=Arial></FONT>&nbsp;</DIV>

<DIV><FONT size=2><FONT face=Arial size=3>void 

vtkOpenGLPolyDataMapper::ReleaseGraphicsResources(vtkWindow *win)<BR>{<BR>&nbsp; 

if (this-&gt;ListId &amp;&amp; win)<BR>&nbsp;&nbsp;&nbsp; {<BR></FONT><FONT 

face=Arial><FONT size=3><STRONG>&nbsp;&nbsp;&nbsp; win-&gt;MakeCurrent();&nbsp; 

?????????(win belog to the vtkRenderWindow class and only has pure virtual 

method: MakeCurrent())<BR></STRONG>&nbsp;&nbsp;&nbsp; 

glDeleteLists(this-&gt;ListId,1);<BR>&nbsp;&nbsp;&nbsp; this-&gt;ListId = 

0;<BR>&nbsp;&nbsp;&nbsp; }<BR>&nbsp; this-&gt;LastWindow = NULL; 

<BR>}</FONT></FONT></DIV></FONT></BODY></HTML>