[jira] [Commented] (PDFBOX-1915) Implement shading with Coons and tensor-product patch meshes

["Sewwandi Wijayaratna (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PDFBOX-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13917526#comment-13917526 ] 

Sewwandi Wijayaratna commented on PDFBOX-1915:
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hello,

I am Sewwandi, and I am a graduate student in electrical and computer engineering. I would like to provide a proposal for this project for gsoc 2014. I am familiar with Java, Maven , JUnit and IntelliJ IDEA. I have basic understanding in this mathematical concepts, but I know I have to learn more. As a first step, I would like to implement one of the above algorithms using Matlab and then I will try to see how to integrate the Java version of that implementation with PDFBox. I would like to write my propsal based on these outcomes. I have checked out the full source code and successfully built and ran a sample using my IDE. If I have any questions I will ask them here. 

Thank you.


> 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
> 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; implement cubic spline interpolation for type 0 (sampled) functions.
> Mentor: Tilman Hausherr (European timezone, languages: german, english, french)



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