[vtkusers] Extending vtkOpenGLRenderer

[Matthew Troke]

I think I've figured out that the abstract New() searches all registered
object factories for an override. My question is if you have 2 modules with
object factories that override the same base object, which one wins out?
And can you ensure that a particular override gets chosen?

On Tue, Nov 13, 2018 at 3:40 PM Matthew Troke <
matthew.troke at avalonholographics.com> wrote:

> 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
>


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

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