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https://issues.apache.org/jira/browse/PDFBOX-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14090978#comment-14090978
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Tilman Hausherr commented on PDFBOX-1915:
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I did some tests without running other stuff on the pc and the result is:
- at 96dpi, trityp4, decahed and pattern is about the same
- at 300dpi, pattern is about the same, but trityp4 and decahed are slower
- ch14 p15 and p20 are about the same at 96dpi, and slightly faster at 300dpi.
trityp4 and decahed have large surfaces, so the hash map might perform poorly.
I've decided to commit your changes for two reasons: 1) it will allow more
common code, 2) there are some slight differences in the rendering of the ch14
file - your implementation has slightly less white artifacts than mine. Likely
because I didn't bother about lines. I did think about it, but dropped the idea
at that time because I thought that a line doesn't have a surface.
> 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, DECAHED.pdf, GWG060_Shading_x1a.pdf, GWG060_Shading_x1a_1.png,
> HSBWHEEL.pdf, Kommunikationsbedingungen-Einlagen_FIDOR-Bank.pdf,
> LATTICE1.pdf, LATTICE2.pdf, McAfee-ShadingType7.pdf,
> Shading2Function2LargeDomain.pdf, Shading2Function2LargeDomain.pdf-1-bad.png,
> Shading2Function2LargeDomain.pdf-1-good.png, Shading2Function2LargeDomain.ps,
> Shadingtype6week1.pdf, TENSOR.pdf, TRITYP4.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,
> axsh02.pdf, axsh02_1_withBBox.png, axsh02_1_withoutBBox.png, ch14.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_1-old.png, eci_1.png, 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, pattern-shading-2-4-idMatrix.pdf, 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,
> type45.pdf, 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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