[vtkusers] Read PNG from in-memory buffer?

[David Gobbi]

You mentioned that QImage.bits() does a "deep copy", but that seems
meaningless for your use case because Qt owns all copies and the returned
pointer will become invalid when the QImage destructs.  It would be
different if you were passing the pointer to another Qt image, because then
Qt could "track" the pointer.

VTK should be the one to create the copy.

    imageImport->CopyImportVoidPointer(image.constBits(),
image.byteCount());

Other than that, your usage of vtkImageImport looks fine.

 - David

On Thu, Sep 29, 2016 at 5:32 AM, Elvis Stansvik <
elvis.stansvik at orexplore.com> wrote:

> 2016-09-29 13:29 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> > 2016-09-29 11:35 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>
> :
> >> 2016-09-29 9:29 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>
> :
> >>> I'd like to read a PNG from an in-memory buffer. Looking at
> >>> vtkPNGReader, it seems it only works with files in the file system. In
> >>> general, is there some way to use the reader classes in VTK with
> >>> in-memory data, or would I have to write my own custom reader?
> >>>
> >>> My need for this is not great, I was simply hoping to be able to keep
> >>> this particular PNG in the Qt resource system (so in the end, embedded
> >>> in my executable), load it using Qt file facilities, and use VTK on
> >>> the read in-memory data.
> >>
> >> I realize now that I can probable use QImage to load/decompress the
> >> image, and pass the uncompressed data to a vtkImageImport, but I can't
> >> find any docs on what format vtkImageImport expects for the pixels.
> >> Anyone know?
> >
> > I had a go at this approach, using QImage::Format_RGBA8888 as I think
> > (?) that's the format vtkImportImage wants, but the resulting image
> > looks garbled when shown in VTK:
> >
> >     // Load image with QImage
> >     QImage image(":/images/orexplore-logo-80x47.png");
> >
> >     // Convert to RGBA8888
> >     image = image.convertToFormat(QImage::Format_RGBA8888);
> >
> >     // Have a look at the image to make sure it's OK
> >     auto debugLabel = new QLabel();
> >     debugLabel->setPixmap(QPixmap::fromImage(image));
> >     debugLabel->show();
> >
> >     // Import into a vtkImageData
> >     auto imageImport = vtkSmartPointer<vtkImageImport>::New();
> >     imageImport->SetDataSpacing(1, 1, 1);
> >     imageImport->SetDataOrigin(0, 0, 0);
> >     imageImport->SetWholeExtent(0, image.width() - 1, 0,
> > image.height() - 1, 0, 0);
> >     imageImport->SetDataExtentToWholeExtent();
> >     imageImport->SetDataScalarTypeToUnsignedChar();
> >     imageImport->SetNumberOfScalarComponents(4);
> >     imageImport->SetImportVoidPointer(image.bits(), 1); // Note:
> > QImage::bits() deep copies
> >     imageImport->Update();
> >
> >     auto mapper = vtkSmartPointer<vtkImageMapper>::New();
> >     mapper->SetInputData(imageImport->GetOutput());
> >
> >     auto actor = vtkSmartPointer<vtkActor2D>::New();
> >     actor->SetMapper(mapper);
> >
> > Anyone know exactly what format vtkImageImport expects, or, if it
> > expects RGBA (unsigned char), why the above won't work?
>
> Whoa. Just found
> http://www.vtk.org/doc/nightly/html/classvtkQImageToImageSource.html
> :) I'll of course use that. Sorry for the noise.
>
> Still interested in why the above approach wouldn't work, out of curiosity.
>
> Elvis
>
> >
> > Elvis
> >
> >>
> >> Elvis
> >>
> >>>
> >>> Elvis
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