[vtkusers] Please Help

[Lisa Avila]

Hello,

Look for glDepthFunc( GL_LEQUAL ) - this is what sets up the function that 
the depth buffer uses. There is no standard function that will do what you 
want since that would require a more complex depth buffer.

Lisa



At 11:32 AM 2/1/2004, Mayuresh Dalal wrote:
>Hi Lisa,
>
>Thank you for your response. Things are a little clearer now because of 
>your input about harware renderering.
>
>I have gone over all the vtkOpenGL* .cxx files, and especially 
>vtkOpenGLRenderWindow.cxx . But I still cannot see the snippet of code 
>where z-values of pixels are compared. I have been looking for the <= 
>function, like you said, but could not find it. Can you please be a little 
>more specific?
>
>Thank You.
>
>
>>From: Lisa Avila <lisa.avila at kitware.com>
>>To: "Mayuresh Dalal" <mayur_vtk at hotmail.com>, vtkusers at vtk.org
>>Subject: Re: [vtkusers] Please Help
>>Date: Sun, 01 Feb 2004 01:48:25 -0500
>>
>>Hello,
>>
>>VTK does use OpenGL (or Mesa) for the hardware rendering. You can find 
>>all the code in the Rendering directory in the vtkOpenGL* files. The 
>>hardware z buffer is used and you can see in vtkOpenGLRenderWindow.cxx 
>>that a less than or equal function is used (a pixel will be overwritten 
>>if the new z value is less than or equal to the one currently stored in 
>>the z buffer).
>>
>>What you are trying to do does not sound straight-forward. The frame 
>>buffer only stores one result per pixel - you want more than one. You 
>>could consult the z buffer after every polygon is drawn and save the 
>>results (adding any changes into your own modified z buffer that can 
>>store multiple results per pixel) but that would be very very slow. There 
>>are some specialized OpenGL extensions supported by some graphics cards 
>>that can help you do this - but again this is not a simple change to the 
>>VTK code base.
>>
>>Lisa
>>
>>
>>
>>
>>
>>
>>At 12:52 AM 2/1/2004, Mayuresh Dalal wrote:
>>>Hi People,
>>>
>>>Please help me......Can someone please tell me which is the method where 
>>>Z-buffering is actually
>>>performed for each pixel?
>>>
>>>I need to modify the way z buffering is performed and also the way Z 
>>>buffer is used for displaying objects/props
>>>
>>>Does vtk rely on OpenGL z-buffering or does it have its own explicit 
>>>z-buffering ?   If, can someone point out the C++ method where 
>>>z-buffering is performed in VTK ?
>>>
>>>Ok, in the terminology that I am used to(might differ with some of you), 
>>>frame buffer is the array in which all pixel info( R,G,B,A,Z) is stored 
>>>and is used to plot indivisual pixels on the screen.
>>>
>>>I want to render 2 objects. Areas of object 2 are occluded behind object 
>>>1.I want to preserve the data corresponding to the OCCLUDED areas, which 
>>>are traditionally eliminated / overwritten in the frame buffer. I want 
>>>to preserve the data so that I can use it when looking at the same 2 objects
>>>from a different camera position.
>>>
>>>how should I go about backing up that info before it is lost/overwritten 
>>>in the framebuffer?
>>>
>>>I need to stop the removal of FRONT FACING , but HIDDEN surfaces.
>>>
>>>Is there a way of doing this?
>>>
>>>Please help me.
>>>
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>
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