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https://issues.apache.org/jira/browse/PDFBOX-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14052074#comment-14052074
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Shaola Ren commented on PDFBOX-1915:
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We are aware of the performance issue at the very beginning, and I talked about
using a better structure to store the CoonsTriangle several times, and I
mentioned sort and search before as well, the situation is the work is not done
yet. For the structure to store the CoonsTriangle, I am thinking about to apply
a Quadtree in the left time, before I did the work, I cannot say more about how
the performance will be, and I can't guarantee anything :). However, if someone
else has a really better suggestion, I am glad to take it.
The answer for "break", you cannot use a break, as there may be more than one
point in the unit patch mapped to the same position of the real patch, two
reasons, one is digitization, the other is folding or overlap. Digitization,
like a length 10 line linearly mapped to only a length 2 line (just assume they
have the same unit), if it's in real space, there is no such problem that more
than one point mapped to the same point, for the non-negative integer space,
the problem exists. Folding, that's obvious, that's why there are priority
rules for type 6 and 7 shading. It looks the macfeeU5.pdf have some overlapped
patches, if a break is used, may cause some unexpected white spots, however, I
didn't try. For other files, a break may not cause such a problem that's just
because the issue is not triggered, you still cannot set a break in the current
code.
"Neighbor hit", that's possible, the same reason as above, you have to check if
there are any other matched triangles for the current structure, however, I
didn't have this in mind before, thanks. I'll look at the attached file.
> 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: CIB-coons-vs-tensormesh.pdf, CIB-coonsmesh.pdf,
> CONICAL.pdf, GWG060_Shading_x1a.pdf, GWG060_Shading_x1a_1.png, HSBWHEEL.pdf,
> McAfee-ShadingType7.pdf, Shadingtype6week1.pdf, TENSOR.pdf, XYZsweep.pdf,
> _gwg060_shading_x1a.pdf-1.png, _mcafee-shadingtype7.pdf-1.png,
> 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, crestron-p9.pdf,
> eci_altona-test-suite-v2_technical_H.pdf, example_030.pdf, failedTest.rar,
> lamp_cairo.pdf, lamp_cairo7_0.png, lamp_cairo7_1.png, lamp_cairo7_1.png,
> lineRasterization.jpg, mcafeeU5.pdf, mcafeeU5_1.png, mcafeeu5.pdf-1.png,
> 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,
> tensor4-nofunction.pdf, tensor4-nofunction.ps, tensor4-nofunction_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, 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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