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The PDF::Writer#text method takes care of all text
wrapping for you, the writer. That means that if your text will not fit
on a single line, then it will be wrapped. If your text will not fit on
a single page, then a new page will automatically be created. The layout
engine in PDF::Writer is extensive and somewhat extensible. By no means
is it capable of replacing a professional layout program (or even a
simple word processor), but it is very good at what it does. Sometimes,
however, it is necessary for the author of a document generation program
to indicate precisely where text should go.
This is when PDF::Writer#add_text and
PDF::Writer#add_text_wrap are useful. The former will take a
string and place it starting at specific (x, y) coordinates. If
the text exceeds the size of the page, it will not stop. The
latter also accepts a text width and writes only as much text from the
original string as will fit in the specified width. The portion of the text
that does not fit will be returned. Both of these methods also accept a
font size (by default, the current PDF::Writer#font_size
will be used) and a text angle. The following code puts our “Hello,
Ruby” text in a different location on the page and at an angle.
require "pdf/writer"
pdf = PDF::Writer.new
pdf.select_font "Times-Roman"
x = pdf.absolute_left_margin
y = pdf.absolute_bottom_margin
pdf.add_text(x, y, "Hello, Ruby.", 72, 45)
pdf.save_as("hello-angle.pdf")
Measurements in PDF documents are by default in points (about 1/72”, or 1/3mm). The coordinate space can be rotated, scaled, and translated, so all measurements are in “userspace units”. The origin coordinate, (0, 0) in PDF is not at the upper left-hand corner, but instead is in the lower left-hand corner of the page. The PDF::Writer text layout engine assumes the default coordinate space size and orientation.
All angular measurements in PDF::Writer (for both text and graphics) are counter-clockwise. The following table shows the approximate degree measurement of hours on a twelve-hour clock face.
| Hour | Angle |
|---|---|
| 1 | 60° |
| 2 | 30° |
| 3 | 0° |
| 4 | 330° |
| 5 | 300° |
| 6 | 270° |
| 7 | 240° |
| 8 | 210° |
| 9 | 180° |
| 10 | 150° |
| 11 | 120° |
| 12 | 90° |
Text documents are useful, but sometimes, as the cliché says, “a picture is worth a thousand words.” PDF fundamentally supports both “sampled” (that is, bitmapped) and drawn vector graphics. PDF::Writer exposes this functionality to the Ruby developer.
PDF::Writer only supports the insertion of JPEG and PNG format images,
and there is limited support for some of the PNG format’s features.
Other formats can be supported by conversion, possibly through
RMagick[11] Images may either be placed at specific points on
the page canvas (with PDF::Writer::Graphics#add_image and
PDF::Writer::Graphics#add_image_from_file) or flowed onto
the page relative to the vertical text writing pointer with
PDF::Writer::Graphics#image.
Images are inserted using one pixel per PDF unit. This means that
images are generally inserted with 72 DPI (dots per inch)[12]
and must be scaled for higher quality printing images. With
#add_image and #add_image_from_file this means
specifying an image display size; #image allows for
relative scaling. The following table shows what an image of 320×240
pixels would need to be at various DPI resolutions and the corresponding
approximate physical image size. Most computer displays are 72 or 96
DPI; “photo-quality” printed images are usually 300 DPI or better.
| DPI | Scale | Pixel Size | Physical Size |
|---|---|---|---|
| 72 | 100% (1.0) | 320×240 | 41/2”×31/4” (113mm × 85mm) |
| 96 | 75% (0.75) | 240×180 | 31/3”×21/2” (85mm × 631/2mm) |
| 300 | 24% (0.24) | 77×58 | 1”×0.8” (27mm × 201/2mm) |
This demo uses the automatic positioning of #image to
insert similar images. Notice that all three image methods return the
image object that was added to the document so that it can be reused (as
it is in the third case). In all three inserts, the images will be
scaled to 75% of their native size, treating them as 96 DPI.
# This code is demo/chunkybacon.rb
require "pdf/writer"
pdf = PDF::Writer.new
pdf.select_font "Times-Roman"
pdf.text "Chunky Bacon!!", :font_size => 72, :justification => :center
# PDF::Writer#image returns the image object that was added.
i0 = pdf.image "../images/chunkybacon.jpg", :resize => 0.75
pdf.image "../images/chunkybacon.png", :justification => :center, :resize => 0.75
# It can reinsert an image if wanted.
pdf.image i0, :justification => :right, :resize => 0.75
pdf.text "Chunky Bacon!!", :font_size => 72, :justification => :center
pdf.save_as("chunkybacon.pdf")
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