What are the meanings of itextpdf pdfcontentbyte addtemplate's parameters

Question

I am using itextpdf to merge some pdfs to a single one. What are the meanings of itextpdf pdfcontentbyte addtemplate's parameters,there is no docs to describe them.

Answer 1

public void addTemplate(PdfTemplate template,
    double a, double b, double c, double d, double e, double f)

The six values a, b, c, d, e, and f are elements of a matrix that has three rows and three columns.

You can use this matrix to express a transformation in a two-dimentional system.

Carrying out this multiplication results in this:

x' = a * x + c * y + e
y' = b * x + d * y + f

The third column in the matrix is fixed: you're working in two dimensions, so you don't need to calculate a new z coordinate.

When studying analytical geometry in high school, you've probably learned how to apply transformations to objects. In PDF, we use a slightly different approach: instead of transforming objects, we transform the coordinate system.

The e and the f value can be used for a translation. The a, b, c, and d value can be used for a rotation and/or scaling operation.

By default the Current Transformation Matrix (CTM) is:

With the addTemplate() method, you can add a Form XObject to a canvas and define a position using e, f, e.g:

canvas.addTemplate(template, 36, 36);

This will add template at coordinate x = 36; y = 36.

By introducing a, b, c, and d, you can also rotate and/or scale the template.

Update: as mentioned in the comments, you might want to use the overloaded methods that accept an AffineTransform parameter if you don't like the Algebra of the transformation matrix.