PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Using Text and Fonts to Create Images
497
Figure 22.6 Coordinates of the bounding box are given relative to the
baseline.The origin of the coordinates is shown here as (0,0).
To get the dimensions of the box, you call
$bbox=imagettfbbox ($font_size, 0, $fontname, $button_text);
This call says,“For given font size $font_size, with text slanted on an angle of zero
degrees, using the TrueType font Arial, tell me the dimensions of the text in
$button_text.”
Note that you actually need to pass the path to the file containing the font into the
function. In this case, it’s in the same directory as the script (the default), so we didn’t
specify a longer path.
The function returns an array containing the coordinates of the corners of the
bounding box.The contents of the array are shown in Table 22.1.
Table 22.1 Contents of the Bounding Box Array
Array Index Contents
0 x coordinate, lower-left corner
1 y coordinate, lower-left corner
2 x coordinate, lower-right corner
3 y coordinate, lower-right corner
4 x coordinate, upper-right corner
5 y coordinate, upper-right corner
6 x coordinate, upper-left corner
7 y coordinate, upper-left corner
To remember what the contents of the array are, just remember that the numbering
starts at the bottom-left corner of the bounding box and works its way around counterclockwise.
There is one tricky thing about the values returned from the imagettfbbox() function.They
are coordinate values, specified from an origin. However, unlike coordinates
for images, which are specified relative to the top-left corner, they are specified relative
to a baseline.
Look at Figure 22.6 again.You will see that we have drawn a line along the bottom
of most of the text.This is known as the baseline. Some letters hang below the baseline,
such as y in this example.These parts of the letters are called descenders.