[vtkusers] How to use SetGeometryShaderCode

[Kumar Ashutosh]

Thanks, Ken for showing interest in this issue.
You were correct that a uniform value was defaulting to 0.0. So I manually
replaced them with a vec2. The line does render now but the behaves only as
a normal line and not as a WideLine. My implementation can be seen here
<https://gist.github.com/thechargedneutron/0cfb5abb9531279bf9f80d6f38410aaf>.
In this code, case1 is the normal line, case2 is with
SetRenderLineAsTubes() and case3 is the manual GS part which I am trying to
implement. I have replaced the uniform vec2 variable lineWidthNVC with
vec2(0.1, 0.1) . This renders as a normal line and not as a Tube. Kindly
see if I am making any mistake in injecting the shader.

Regards,
Kumar Ashutosh
ᐧ

On Mon, Jul 9, 2018 at 8:54 PM, Ken Martin <ken.martin at kitware.com> wrote:

> Using your own shader code is a bit advanced as there are a few moving
> parts. If you specify geometry shader code then you also have to make sure
> the right uniforms/arrays are being set for that shader code. That would be
> my guess as to the issue with your attempt to manually specify wide lines.
> Maybe the code is fine but some uniforms are not properly set and so are
> defaulting to 0.0 etc.
>
> I agree an example of geometry replacements would be good. If you get
> something working let me know and I'll add it to the wiki page on custom
> shaders.
>
> On Wed, Jul 4, 2018 at 9:11 AM, Kumar Ashutosh <
> kumar.ashutosh.ee at gmail.com> wrote:
>
>> I want to add custom Geometry Shader to my mapper. From the source code,
>> I concluded that in vtkOpenGLPolyDataMapper we can inject custom Shader
>> Code. Also, the code has WideLineGS as the default Geometry Shader. I tried
>> to mimic the same behaviour by injecting the same code as given here
>> <https://gitlab.kitware.com/vtk/vtk/blob/master/Rendering/OpenGL2/glsl/vtkPolyDataWideLineGS.glsl> (source
>> code of WideLinesGS)  using the function SetGeometryShaderCode. The
>> resulting screen is a blank screen with no errors raised.
>>
>> Can someone please guide me on how to inject Geometry Shader Code. This
>> is specific to Geometry Shader only as I have successfully tried with Frag
>> Shader and Vertex Shader.
>> A simple example of this would be great.
>>
>> Regards,
>> Kumar Ashutosh
>> ᐧ
>>
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>
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