[vtkusers] Need help integrating VTK with an existing OpenGL application (translating glFrustum and gluLookAt calls to VTK)

[Weiguang Guan]

Read chapter 3 of the Red Book 
http://www.glprogramming.com/red/chapter03.html, focusing on subsection 
"Perspective Projection".

Weiguang

On Thu, 3 Jan 2008, Alethea Bair wrote:

> That's not quite correct. There is no way to use glPerspective to get
> non-regular trapezoids for the frustum shape. glFrustum does allow this.
> Unfortunately, I don't know enough about vtkCamera to give advice there.
>
> -Alethea
>
>> You can calculate the values of six arguments of glFrustum from the four
>> arguments of gluPerspective, and vice versa.
>>
>> Weiguang
>>
>> On Thu, 3 Jan 2008, Mark Waligora wrote:
>>
>>> Weiguang,
>>>
>>> Thanks for the reply.  I have no problem using the vtk classes in place
>>> of
>>> code that I already have.  My issue is that I'm not certain how to use
>>> the
>>> vtkCamera in place of my glFrustum call when I am creating a frustum
>>> where,
>>> for example, both the left and right sides of the front face of the
>>> frustum
>>> volume lie on the negative side of the y axis.  From what I can tell,
>>> the
>>> vtkCamera can be given a viewing angle and a near and far plane, but
>>> that
>>> gives me the equivalent control of a gluPerspective call, which is more
>>> limited than the functionality that glFrustum provides.  I noticed there
>>> was
>>> a function to multiply in additional matrices to the camera's
>>> transformation
>>> matrix, but I don't think that would be quite what I want either.
>>>
>>> -Mark Waligora
>>>
>>> On Jan 3, 2008 1:08 PM, Weiguang Guan <guanw at rhpcs.mcmaster.ca> wrote:
>>>
>>>> Hi Mark,
>>>>
>>>> If you decide to move on to vtk, then you shouldn't called gl commands
>>>> directly. vtkCamera contains methods that implement what you want to
>>>> do.
>>>>
>>>> Weiguang
>>>>
>>>> On Thu, 3 Jan 2008, Mark Waligora wrote:
>>>>
>>>>> Hey all,
>>>>> I've done quite a bit of searching and reading and am having some
>>>> trouble
>>>>> getting started integrating VTK into my application.  I'm a new user,
>>>> but
>>>>> I've spent enough time looking that I don't think I'm missing anything
>>>> too
>>>>> obvious.
>>>>>
>>>>> I have a fairly simple visualization application written with OpenGL.
>>>>> I
>>>>> want to visualize some more complicated data sets, so I wanted to
>>>>> write
>>>> a
>>>>> version that works with VTK.
>>>>>
>>>>> My visualization application is fed in data from a motion capture
>>>> system, so
>>>>> right now, every time my application loop updates, it reads the data
>>>> from
>>>>> the mo-cap system, and updates the rendering with very specific calls
>>>>> to
>>>>> glFrustum and gluLookAt.  The front face of the frustum volume is
>>>>> almost
>>>>> never centered around the z axis, so I can't simulate the frustum
>>>> creation
>>>>> by simply providing a vtkCamera with a position, direction, and
>>>>> viewing
>>>>> angle.  I need more control of the frustum shape than that
>>>>> functionality
>>>>> seems to provide.
>>>>>
>>>>> Can anyone advise me on how to create a simple vtk application with no
>>>> user
>>>>> control where the frustum and camera position are automatically
>>>>> updated
>>>> by
>>>>> the program every cycle of the main program loop?  From what I can
>>>>> tell,
>>>> I
>>>>> don't want to use an interactor since the user will not be interacting
>>>> with
>>>>> the application (the user interacts with the motion capture system,
>>>>> and
>>>> the
>>>>> application simply queries data from the motion capture system when it
>>>> is
>>>>> rendering).  Again, I need to be able to create frustums that aren't
>>>>> centered around the z axis.
>>>>>
>>>>> Thanks in advance!
>>>>>
>>>>> -Mark Waligora
>>>>>
>>>>
>>>
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>
>