[vtkusers] How to get the framebuffer

[Mathieu Westphal]

Hi,

You will need to share more code in order to get help.
The test I mentioned is working perfectly here.

Mathieu Westphal

On Wed, Jul 25, 2018 at 4:46 PM, Ken Martin <ken.martin at kitware.com> wrote:

> In current VTK I cannot see how GetPixelData can return null unless new
> returns null due to being out of memory. The code boils down to
>
>   unsigned char* ucdata = new unsigned char[width * height * 3];
>   vtkRecti rect(x_low, y_low, width, height);
>   this->ReadPixels(rect, front, GL_RGB, GL_UNSIGNED_BYTE, ucdata, right);
>   return ucdata;
>
> So if the return value is nullptr then "new" failed. So check around maybe
> something else funny is going on.
>
>
> On Wed, Jul 25, 2018 at 10:24 AM, Mathieu Westphal <
> mathieu.westphal at kitware.com> wrote:
>
>> Hi,
>>
>> It should work then.
>>
>> Take a look into :
>> VTK/Rendering/OpenGL2/Testing/Cxx/TestRenderToImage.cxx
>> VTK/Rendering/Core/vtkWindowToImageFilter.cxx
>>
>> Both are doing exactly what you are trying to do.
>> The first one (the test) may be very useful to you.
>>
>> Best regards,
>>
>> Mathieu Westphal
>>
>> On Wed, Jul 25, 2018 at 4:20 PM, ling Hai <qyaoza at gmail.com> wrote:
>>
>>> Hi Mathieu,
>>> Thank you for the response, I am already calling renderWindow->Render().
>>> I tried reading the front, back, left and right buffers but am still unable
>>> to get any data from the call. If it helps, I am not using shaders, color
>>> points, or opacity the blending mode is composite, it is rendered by the
>>> gpu.
>>>
>>> Linghai
>>>
>>> On Wed, Jul 25, 2018 at 3:52 AM, Mathieu Westphal <
>>> mathieu.westphal at kitware.com> wrote:
>>>
>>>> Hi LingHai
>>>>
>>>> Make sure you have rendered into the renderWindow first.
>>>> (renderWindow->Render())
>>>> And try to read from the front and the back buffer.
>>>>
>>>> Best regards,
>>>>
>>>> Mathieu Westphal
>>>>
>>>> On Tue, Jul 24, 2018 at 7:57 PM, ling Hai <qyaoza at gmail.com> wrote:
>>>>
>>>>> Hi,
>>>>> I am new to vtk and I am trying to get the front framebuffer from the
>>>>> renderwindow like this:
>>>>> int * dim = renderWindow->GetSize();
>>>>> unsigned char* pixels = renderWindow->GetPixelData(0,0
>>>>> ,dim[0]-1,dim[1]-1,true);
>>>>>
>>>>> but in pixels there is only a null value. I am using this on a 3d
>>>>> render if that makes a difference the above segment of code called after
>>>>> rendering the volume. What am I missing? Any help is appreciated thanks.
>>>>> Linghai
>>>>>
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>
>
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