Drawing Circles with Alpha Blending

This PHP program demonstrates how to draw circles on an image with blending based on the alpha channel with the Graphics Draw, GD, library.

DrawingCirclesWithAlpha.php

<?php
  // Create a 400 by 400 pixel image
  $qImage = imagecreatetruecolor(400, 400);
  // Create a color for the image: (Image, Red, Green, Blue)
  $qWhite = imagecolorallocate($qImage, 255, 255, 255);

  // Use imagesx() and imagesy() to draw a rectangle over the entire image
  // Format: (Image, UpLeftX, UpLeftY, LowRightX, LowRightY, Color)
  imagefilledrectangle($qImage, 0, 0, imagesx($qImage), imagesy($qImage), $qWhite);

  for($i = 0; $i < 256; $i = $i + 20) {
    // Alpha value run from 0 to 127 with 127 being transparent
    $qAlphaColor = imagecolorallocatealpha($qImage, $i, 0, 0, 80 + ceil(rand(0,30)));
    // Format: (Image, CenterX, CenterY, Width, Height, Color)
    imagefilledellipse($qImage, $i, $i, $i, $i, $qAlphaColor);
  }

  header("content-type: image/png");
  imagepng($qImage);
  imagedestroy($qImage);
?>

Output