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

Creating Images
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Figure 22.1
The script draws a blue background and then adds a line and a
text label for the image.
Now let’s walk through the steps of creating this image one by one.
Creating a Canvas Image
To begin building or changing an image in PHP, you need to create an image identifier.
There are two basic ways to do this. One is to create a blank canvas, which you can do with
a call to the imagecreatetruecolor() function, as done in this script with the following:
$im = imagecreatetruecolor($width, $height);
You need to pass two parameters to ImageCreateTrueColor().The first is the width of
the new image, and the second is the height of the new image.The function will return
an identifier for the new image.These identifiers work a lot like file handles.
An alternative way is to read in an existing image file that you can then filter, resize, or
add to.You can do this with one of the functions imagecreatefrompng(), imagecreatefromjpeg(),
or imagecreatefromgif(), depending on the file format you are reading in.
Each of these functions takes the filename as a parameter, as in this example:
$im = imagecreatefrompng(‘baseimage.png’);
An example is shown later in this chapter using existing images to create buttons on
the fly.
Drawing or Printing Text on the Image
Drawing or printing text on the image really involves two stages. First, you must select
the colors in which you want to draw. As you probably already know, colors to be displayed
on a computer monitor are made up of different amounts of red, green, and blue
light. Image formats use a color palette that consists of a specified subset of all the possible
combinations of the three colors.To use a color to draw in an image, you need to