[vtk-developers] Proposed fix for vtkOpenGLTexture

[Ken Martin]

You can do this in VTK as is using vtkTextureObject->Create2DFromRaw and
then vtkTexture->SetTextureObject.

But I don't have an issue with your suggested change provided it passes
testing.



On Tue, Feb 19, 2019 at 11:48 AM Patrick Bergeron <pbergeron at spiria.com>
wrote:

> Hello. I sent a recent email stating I needed to pass arbitrary data to a
> shader, encoded in a texture of float format.
>
>
> Unfortunately, my shader only received texels with values clamped between
> 0-1.  As you can imagine, this is a problem.
>
>
> I have traced the problem down to vtkOpenGLTexture::Load() function.
>
>
> What Load() does is :
>
> - Checks number of inputs. If 1, normal texture. If 6, cubemap texture.
> (OK)
>
> - Gets the image scalars (aka pixels) and number of components (aka:
> channels)   (OK)
>
>
> - Calls MapScalarsToColor if not depth map, or if colormpde is
> Map_Scalars, or* if datatype is NOT unsigned char.  (UGH!)*
>
>
> - Resizes the input of the source exceeds GL's internal
> dimension capacity. (OK)
>
> - Resamples the image if needed. (OK)
>
>
> - Creates a 1-channel floating point depth image, if it's a depth texture,
> by calling CreateDepthFromRaw(). (OK)
>
>   (or, if not a depth map)
>
> - Creates a 3 or 4-channel cube map, or normal texturemap, by specifying
> the new converted data type of VTK_UNSIGNED_CHAR.
>
>
>
> There is actually very little to do to support arbitrary float data:
> Simply avoid remapping to unsigned char if the data is float (unless
> there's intentional remapping by using such ColorMode), and pass the actual
> format down to CreateXXXFromRaw()
>
>
>
> My proposed change is to not convert incoming float data to unsigned char,
> but rather, to leave float color data alone.
>
>
> Edit:
>
>
> Change this (eg: remove red line)
>
>
> *        if (this->IsDepthTexture != 1 &&*
> *          (this->ColorMode == VTK_COLOR_MODE_MAP_SCALARS ||*
> *           inscalars->GetDataType() != VTK_UNSIGNED_CHAR ))*
>
> *         {           dataPtr[i] = this->MapScalarsToColors (inscalars);
>         bytesPerPixel = 4;         } *
> to this:
>
> *        if (this->IsDepthTexture != 1 &&*
>
> *          (this->ColorMode == VTK_COLOR_MODE_MAP_SCALARS)) *
> *        {*
> *          dataPtr[i] = this->MapScalarsToColors (inscalars);*
> *          bytesPerPixel = 4;*
> *        }*
>
>
> and these:
>
>
>
> *           this->TextureObject->CreateCubeFromRaw(             xsize,
> ysize, bytesPerPixel, VTK_UNSIGNED_CHAR, vtmp);
> this->TextureObject->Create2DFromRaw(             xsize, ysize,
> bytesPerPixel, VTK_UNSIGNED_CHAR, resultData[0]); *
>
> to these:
>
>           this->TextureObject->CreateCubeFromRaw(
>             xsize, ysize, bytesPerPixel, dataType, vtmp);
>
>
>           this->TextureObject->Create2DFromRaw(
> *             xsize, ysize, bytesPerPixel, dataType, resultData[0]); *
>
>
> And that's all there is to it.
>
> Does anyone have any objection?  The only side effect I can imagine is
> that more texture memory is consumed iff the source image data is float and
> no remapping is desired. With recent GPU hardware, I'd be surprised if this
> was a problem.
>
> In any case, with this change, we can effectively pass unclamped
> arbitrary floating-point data buffers to shaders to be used for advanced
> viz techniques.
>
> Thanks
> Patrick Bergeron
>
>
>
>
>
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-- 
Ken Martin PhD
Distinguished Engineer
Kitware Inc.
101 East Weaver Street
Carrboro, North Carolina
27510 USA

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