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

498 Chapter 22 Generating Images
The left side of the baseline is specified as the origin of measurements—that is, x
coordinate 0 and y coordinate 0. Coordinates above the baseline have a positive x coordinate,
and coordinates below the baseline have a negative x coordinate.
In addition, text might actually have coordinate values that sit outside the bounding
box. For example, the text might actually start at an x coordinate of –1.
What this all adds up to is the fact that care is required when you’re performing calculations
with these numbers.
You work out the width and height of the text as follows:
$right_text = $bbox[2]; // right co-ordinate
$left_text = $bbox[0]; // left co-ordinate
$width_text = $right_text - $left_text; // how wide is it?
$height_text = abs($bbox[7] - $bbox[1]); // how tall is it?
After you have this information, you test the loop condition:
} while ( $font_size>8 &&
( $height_text>$height_image_wo_margins ||
$width_text>$width_image_wo_margins )
);
You test two sets of conditions here.The first is that the font is still readable; there’s
no point in making it much smaller than 8-point type because the button becomes too
difficult to read.The second set of conditions tests whether the text will fit inside the
drawing space you have available for it.
Next, you check to see whether the iterative calculations found an acceptable font
size and report an error if not:
if ( $height_text>$height_image_wo_margins ||
$width_text>$width_image_wo_margins )
{
// no readable font size will fit on button
echo ‘Text given will not fit on button.’;
}
Positioning the Text
If all was okay, you next work out a base position for the start of the text.This is the
midpoint of the available space.
$text_x = $width_image/2.0 - $width_text/2.0;
$text_y = $height_image/2.0 - $height_text/2.0 ;
Because of the complications with the baseline relative coordinate system, you need to
add some correction factors:
if ($left_text < 0)
$text_x += abs($left_text);
// add factor for left overhang