Tilman Hausherr created PDFBOX-1915:
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Summary: 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
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 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.
You are not starting from scratch. The implementation of type 4 and 5 shows you
how to do the basics (read the parameters from the PDF, set the graphics),
except for the math. 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.
Testing:
I will attach 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
Mentor: Tilman Hausherr (European timezone, languages: german, english, french)
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