[vtkusers] Extending vtkOpenGLRenderer

[Matthew Troke]

What I don't understand is how does vtkRenderer::New() know what type of
renderer to create? Normally, this would be a vtkOpenGLRenderer, so
something must be telling VTK to override the class type with
vtkOpenGLRenderer. How do I tell my application to create a
vtkMyOpenGLRenderer instead? I don't know what you mean by "manipulate the
object factory".

Matt

On Tue, Nov 13, 2018 at 3:22 PM Marcus D. Hanwell <
marcus.hanwell at kitware.com> wrote:

> On Tue, Nov 13, 2018 at 1:00 PM Matthew Troke <
> matthew.troke at avalonholographics.com> wrote:
>
>> I am adding a new module to VTK that extends vtkOpenGLRenderer (let's
>> call it vtkMyOpenGLRenderer). I would like to be able to use this in an
>> application such that when I instantiate a vtkRenderer (such as with
>> vtkRenderer::New()), it creates a vtkMyOpenGLRenderer. I'm not clear on the
>> correct way to set this up via CMake. Do I need to create a new backend, or
>> just enable the object factory?
>>
>
> This is really just a runtime thing, and you would achieve it by
> manipulating the object factory. All the CMake code does is ensure the
> appropriate calls are made before any of the classes are instantiated, as
> part of your application start up logic you would want to remove the
> standard vtkOpenGLRenderer override, and add your own. You don't even need
> this to be in a module, it just needs to derive from the vtkRenderer class
> so that it is possible to return a vtkRenderer pointer from the static
> ::New() method.
>
> Hope that makes sense, the entire object factory thing is runtime. We just
> added convenience functions in the form of defines passed into the build
> system, or calls you can add to your code that is compiled into your
> application somewhere.
>


-- 
Matthew Troke
Software Engineer
Office: 1-709-701-0239
Email: matthew.troke at avalonholographics.com

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