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https://issues.apache.org/jira/browse/PDFBOX-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13925293#comment-13925293
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Sergey Smal commented on PDFBOX-1915:
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Hello, my name is Sergey Smal, I'm student of MIPT from Russia.
I'm plannig to take part in GSoC 2014 and find that issue very interesting for
me.
I've already tested pdfbox-app-1.8.4 with some PDFs and look through code from
repository.
I think that I can solve this issue because I have rather good mathematical
background and experience in java programming.
BTW: have some experience with "cubic Bezier curves". I found bug and proposed
a solution of it in [degrfa
library|https://code.google.com/p/degrafa/issues/detail?id=100]
Is PDF specification is all that I need to implement type 6 and 7 of shading
methods?
If you have any additional links for those methods, can you share them?
> Implement shading with Coons and tensor-product patch meshes
> ------------------------------------------------------------
>
> Key: PDFBOX-1915
> URL: https://issues.apache.org/jira/browse/PDFBOX-1915
> Project: PDFBox
> Issue Type: Improvement
> Components: Rendering
> Affects Versions: 2.0.0
> Reporter: Tilman Hausherr
> Labels: graphical, gsoc2014, java, math, shading
> Attachments: CONICAL.pdf, HSBWHEEL.pdf, McAfee-ShadingType7.pdf,
> TENSOR.pdf, XYZsweep.pdf, asy-coons-but-really-tensor.pdf, asy-tensor.pdf,
> lamp_cairo.pdf
>
>
> Of the seven shading methods described in the PDF specification, type 6
> (Coons patch meshes) and type 7 (Tensor-product patch meshes) haven't been
> implemented. I have done type 1, 4 and 5, but I don't know the math for type
> 6 and 7. My math days are decades away.
> Knowledge prerequisites:
> - java, although you don't have to be a java ace, just feel confortable
> - math: you should know what "cubic Bézier curves", "Degenerate Bézier
> curves", "bilinear interpolation", "tensor-product", "affine transform
> matrix" and "Bernstein polynomials" are, or be able to learn it
> - maven (basic)
> - svn (basic)
> - an IDE like Netbeans or Eclipse or IntelliJ (basic)
> - ideally, you are either a math student who likes to program, or a computer
> science student who is specializing in graphics.
> A first look at PDFBOX: try the command utility here:
> https://pdfbox.apache.org/commandline/#pdfToImage
> and use your favorite PDF, or the PDFs mentioned in PDFBOX-615, these have
> the shading types that are already implemented.
> Some simple source code to convert to images:
> String filename = "blah.pdf";
> PDDocument document = PDDocument.loadNonSeq(new File(filename), null);
> List<PDPage> pdPages = document.getDocumentCatalog().getAllPages();
> int page = 0;
> for (PDPage pdPage : pdPages)
> {
> ++page;
> BufferedImage bim = RenderUtil.convertToImage(pdPage,
> BufferedImage.TYPE_BYTE_BINARY, 300);
> ImageIO.write(bim, "png", new File(filename+page+".png"));
> }
> document.close();
> You are not starting from scratch. The implementation of type 4 and 5 shows
> you how to read parameters from the PDF and set the graphics. You don't have
> to learn the complete PDF spec, only 15 pages related to the two shading
> types, and 6 pages about shading in general. The PDF specification is here:
> http://www.adobe.com/devnet/pdf/pdf_reference.html
> The tricky parts are:
> - decide whether a point(x,y) is inside or outside a patch
> - decide the color of a point within the patch
> To get an idea about the code, look at the classes GouraudTriangle,
> GouraudShadingContext, Type4ShadingContext and Vertex here
> https://svn.apache.org/viewvc/pdfbox/trunk/pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/shading/
> or download the whole project from the repository.
> https://pdfbox.apache.org/downloads.html#scm
> If you want to see the existing code in the debugger with a Gouraud shading,
> try this file:
> http://asymptote.sourceforge.net/gallery/Gouraud.pdf
> Testing:
> I have attached several example PDFs. To see which one has which shading,
> open them with an editor like NOTEPAD++, and search for "/ShadingType"
> (without the quotes). If your images are rendering like the example PDFs,
> then you were successful.
> Optional:
> Review and optimize the complete shading package for speed; implement cubic
> spline interpolation for type 0 (sampled) functions (that one is really
> low-low priority, see details by looking up "cubic spline interpolation" in
> the PDF spec, which tells that it is disregarded in printing, and I don't
> have a test PDF).
> Mentor: Tilman Hausherr (European timezone, languages: german, english,
> french)
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