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From "Tilman Hausherr (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PDFBOX-1915) Implement shading with Coons and tensor-product patch meshes
Date Tue, 03 Jun 2014 14:07:01 GMT

    [ https://issues.apache.org/jira/browse/PDFBOX-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14016536#comment-14016536

Tilman Hausherr commented on PDFBOX-1915:

Wonderful news :-)

About the images that can't be displayed: there is always the possibility that it is one of
the problems what appears with some of the other shadings, i.e. that getRaster() is never

About the McAfee file: I don't think it is because of the order. However that file has one
difference: BitsPerCoordinate is 32 and not 24 as many others. In my code in GouraudShadingContext,
the color value is read into an int which maybe wasn't a good idea. Try to change your code
(in Type7ShadingContext.readTensorPatch() ) to read it into a long and see what happens. Look
at the debugging to see whether the values change.

> 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: 1.8.5, 1.8.6, 2.0.0
>            Reporter: Tilman Hausherr
>            Assignee: Shaola Ren
>              Labels: graphical, gsoc2014, java, math, shading
>             Fix For: 2.0.0
>         Attachments: CONICAL.pdf, GWG060_Shading_x1a.pdf, HSBWHEEL.pdf, McAfee-ShadingType7.pdf,
Shadingtype6week1.pdf, TENSOR.pdf, XYZsweep.pdf, asy-coons-but-really-tensor.pdf, asy-tensor-rainbow.pdf,
asy-tensor.pdf, coons-function.pdf, coons-function.ps, coons-nofunction-CMYK.pdf, coons-nofunction-CMYK.ps,
coons-nofunction-Duotone.pdf, coons-nofunction-Duotone.ps, coons-nofunction-Gray.pdf, coons-nofunction-Gray.ps,
coons-nofunction-RGB.pdf, coons-nofunction-RGB.ps, coons2-function.pdf, coons2-function.ps,
coons4-function.ps, eci_altona-test-suite-v2_technical_H.pdf, lamp_cairo.pdf, pass4FlagTest.rar,
patchCases.jpg, patchMap.jpg, shading6ContourTest.rar, shading6Done.rar, shading7.rar, tensor-nofunction-RGB.pdf,
tensor-nofunction-RGB.ps, tensor-nofunction-RGB_1.png, updateshading6ContourTest.rar
> 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,
> 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
> 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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