2 Module Reference🔗ℹ

This module is automatically provided by #lang bookcover. The only difference between the require form and #lang bookcover is that with the former, finish-cover is not automatically called at the end of your program. You might prefer to use the require form when doing something fancier than creating just a single static cover; for example, when defining your own functions that create multiple book covers of the same style for different titles.

The cover dimensions are calculated as follows:

1. The width and height of the first page in interior-pdf are used as the size of the front and back covers.

2. The page count of interior-pdf is passed to spinewidth-calc to determine the width of the spine. (See spine width calculators.)

3. A width equal to bleed-pts is added to all four edges of the cover.

Examples:

; The minimum viable setup call

(setup #:interior-pdf "my-book-contents.pdf"

#:cover-pdf "cover.pdf")

; Using more options:

(setup #:interior-pdf "my-book-contents.pdf"

#:cover-pdf "cover.pdf"

#:spinewidth-calc (using-ppi 339) ; Calculate spine width using 339 PPI

#:bleed-pts (inches->pts 0.25))   ; Use 1/4" bleed

If setup has not yet been called since the start of the program, or if it hasn’t been called since the last time finish-cover was called, then there is no active cover, and current-cover-dc will return null.

If current-cover-dc is already null, calling this function has no effect.

This function is automatically called at the very end of your program when using #lang bookcover.

It is also called automatically on successive calls to setup whenever current-cover-dc is not equal to null.

2.1 Spine width calculators🔗ℹ

In order to properly calculate the overall width of the book cover, the module needs (among other things) a way to calculate the thickness of your book’s spine.

This spine width calculator is any function that takes a page count (a positive integer) and returns a value in points.

You may pass any such function to the #:spine-calculator argument of setup; if you choose not to, setup will default to the function returned by (createspace-spine 'white-bw) — that is, it will assume you are having your book printed by Createspace, on their white paper, in black and white.

Different printers specify different ways of calculating the spine width of your book. As a convenience, this module provides some functions which return ready-made spine width calculators that cover the most common cases, but you can also supply your own.

Use this if your printing service instructs you to calculate spine width using a PPI value for a particular paper type.

2.2 Drawing functions🔗ℹ

; These two lines do exactly the same thing:

(cover-draw pic 0 0)

(backcover-draw pic)

; These two lines also do exactly the same thing:

(cover-draw pic (spinerightedge) 0)

(frontcover-draw pic)

The 0 coordinates for either function’s #:top argument (as well as the #:left argument of backcover) start at the very outside edge of the bleed.

When hcenter is #t, left is ignored; likewise when vcenter is #t, top is ignored.

By design, this function does not check or care if pic will fit inside spinewidth.

; Draw some text on the spine

(define spine-title

(text "My Book Title" "Helvetica" 10 (degrees->radians 270)))

(spine-draw spine-title (centering-offset spine-title page-height pict-height))

; Draw a blue rectangle that wraps around the spine equally on front and back

(define spine-rectangle

(filled-rectangle (* (spinewidth) 4)

(pageheight)

#:color "lightblue"

#:draw-border #f))

(spine-draw spine-rectangle)

2.3 Measurement functions🔗ℹ

When setting up your cover, everything is specified in points. But when you ask Racket for the dimensions of the PDF object you’ve just created, you’ll get a different value than the point value you specified. This is because PDF objects in Racket also have a scaling factor (0.8 by default) that is applied to each dimension when the object is created. So if you specify that your cover should have a bleed of 9 points (1/8 inch), the “actual” width — the one returned by the bleed function — will be generally be 11.25. These scaled values are the ones you must use when drawing on the cover.

The pagewidth, pageheight and coverwidth functions each include the width of the bleed on all applicable sides:

• The (pagewidth) includes the width of the bleed along one edge (i.e. the right edge for the front cover, the left edge for the back cover).

• The (coverwidth) and (pageheight) include the width of the bleed along two edges (top and bottom for height, left and right for width).

If centering vertically, use pict-height as the last argument.

2.4 Testing🔗ℹ

This PDF can be useful for mocking up a cover if you don’t yet have a PDF of your book’s interior to pass to the setup function, or for rapidly experimenting with different paper sizes. See the documentation for check-cover for an example.

2.5 Unit conversion functions🔗ℹ