A Close Look at the GD Library in PHP - An alternative way to create image streams from scratch

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In accordance with the concepts that I expressed in the earlier section, the GD extension offers yet another function that is very useful for creating image streams from scratch. I'm talking about the "imagecreatetruecolor()" function, which can be used in the following way:

// example of 'imagecreatetruecolor()', 'imagecolorallocate()',
'imagestring()' functions
try{
   if(!$image=imagecreatetruecolor(300,200)){
     throw new Exception('Error creating blank image');
   }
   // create text color for image
   if(!$textColor=imagecolorallocate($image,255,255,255)){
     throw new Exception('Error creating text color');
   }
   // include text string into image stream
   if(!$text=imagestring($image,5,10,90,'This is a sample text
string.',$textColor)){
     throw new Exception('Error creating image text');
   }
   header("Content-type:image/png");
   // display image
   imagepng($image);
   // free up memory
   imagedestroy($image);
}
catch(Exception $e){
   echo $e->getMessage();
   exit();
}

As illustrated previously, the "imagecreatetruecolor()" functions behaves very similar to its cousin "imagecreate()" covered in the prior section. However, in this case, the function in question creates a true color image stream, which can be slightly more useful if you want to generate obviously true-color graphics. Other than that, the function takes up the same input parameters, and returns an image identifier if the stream has been successfully created.

That being explained, the image outputted to the browser by the previous example is depicted below:

In addition, the source code of the previous example could be easily wrapped into a custom function, in the following manner:

// example of 'imagecreatetruecolor()', 'imagecolorallocate()',
'imagestring()' functions
try{
   function displayTextOnImage($text='This is a sample text
string'){
     if(!$text){
       throw new Exception('Invalid text string'); 
     }
     if(!$image=imagecreatetruecolor(300,200)){
       throw new Exception('Error creating blank image');
     }
     // create text color
     if(!$textColor=imagecolorallocate($image,255,255,255)){
       throw new Exception('Error creating text color');
     }
     // include text string into image stream
     if(!imagestring($image,5,10,90,$text,$textColor)){
       throw new Exception('Error creating image text');
     }
     header("Content-type:image/png");
     // display image
     imagepng($image);
     // free up memory
     imagedestroy($image); 
   }
   displayTextOnImage('This text was created with GD.');
}
catch(Exception $e){
   echo $e->getMessage();
   exit();
}

All right, at this point, after studying all of the code samples, you'll have to agree with me that building dynamic graphics from scratch by using the GD extension is actually a very intuitive process that can be performed with minor hassles.

Therefore, provided that you have already grasped the programming logic required to create basic images with this powerful graphical extension, in the following section I'll show you some additional hands-on examples aimed at demonstrating how to build dynamic graphics from an existing GIF image, using practically the same GD functions that you learned previously. Sounds really interesting, right?

To learn more on how to create image streams from an existing GIF image using the functionality provided by the GD extension, jump ahead and read the next few lines. I'll be there, waiting for you.

Next: Generating dynamic streams from existing GIF images with the GD library >>
 

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