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

["Tilman Hausherr (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PDFBOX-1915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14082427#comment-14082427 ] 

Tilman Hausherr edited comment on PDFBOX-1915 at 8/1/14 6:10 PM:
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The change I just made deals with larger domains (see the attached Shading2Function2LargeDomain* files), I got a rendered image with stripes before the change. The cause was that the function was returning negative color values or color values larger than 1. Luckily the fix is not only straightforward, but also in the spec:
{quote}
If the value returned by the function for a given colour component is out of range, it shall be adjusted to the nearest valid value.
{quote}


was (Author: tilman):
The change I just made deals with larger domains (see the Shading2Function2LargeDomain* files), I got a rendered image with stripes before the change. The cause was that the function was returning negative color values or color values larger than 1. Luckily the fix is not only straightforward, but also in the spec:
{quote}
If the value returned by the function for a given colour component is out of range, it shall be adjusted to the nearest valid value.
{quote}

> 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_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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