Here are some quick examples:

1

2

3

If we zoom in on example #1, which starts with black (#000000) and has deltas of 4, 1, 0.25, we see the following:

The diagram shows the first ten rows of the gradient. The delta values are accumulated with each row, and only the whole part of the resulting color value is used (aka I take the floor of each color bit). So in this example, using the fractional delta of 0.25 results in exactly one additional blue bit every four rows. Ahhh, perfect!

The Code

No need to use some fancy new language, I wrote a simple PHP program to handle commandline input and output a perfect PNG gradient. The interesting part is the function that generates and saves the gradient:

function build_image($filename, $w, $h, $color, $delta) {
  $img = imagecreatetruecolor($w, $h);
 
  $c = imagecolorallocate($img, $color[0], $color[1], $color[2]);
  $d = $delta;
 
  for ($y = 0; $y < $h; $y++) {
    imagefilledrectangle($img, 0, $y, $w - 1, $y + 1, $c);
 
    $c = imagecolorallocate($img,
      clamp(floor($color[0] + $d[0])),
      clamp(floor($color[1] + $d[1])),
      clamp(floor($color[2] + $d[2]))
    );
 
    $d = array($d[0] + $delta[0], $d[1] + $delta[1], $d[2] + $delta[2]);
  }
 
  imagepng($img, $filename);
  imagedestroy($img);
}

The code is straight forward. First, create the image via imagecreatetruecolor(). Then, starting with the starting color, draw a one pixel tall rectangle for each row of the image. The next row’s color is computed in each iteration by adding the accumulated delta to the starting color. Finally, output the image as a PNG via imagepng() and free the memory. The complete php source can be downloaded here.

Button Time

Once we have our perfect gradient engine in place, it’s time to make some perfect buttons. To achieve the standard glass button look-and-feel, I typically fuse two gradients together: light on the top, dark on the bottom.

Here are the two halves of a pretty red button, along with their starting color and deltas:

And the two commandline invocations of gradient.php to create the gradients:

php gradient.php 100x16 ff8080 -3,-3,-3 top.png
php gradient.php 100x16 d23c3c -3,-3,-3 bottom.png

If I want my buttons to be sexy, rounded corners are a must. My favorite photoshop trick to create multiple rounded buttons is to use a rounded alpha-transparent button with each gradient as a clipping mask. Using a clipping mask is a simple way to guarantee button geometry remains fixed while colors are changed.

Here is the layers pane showing the two gradients fused together and used as a clipping mask for the rounded alpha-transparent button:

The result is a horizontally stretchable gradient button, that doesn’t look half bad. See for yourself:

Custom UIButton

The final button asset can be used as desired, but here is a simple Objective-C example since I’ve been in iPhone world lately:

UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
[btn setFrame:CGRectMake(20, 20, 140, 32)];
[btn setBackgroundImage:[[UIImage imageNamed:@"btn-red.png"]
      stretchableImageWithLeftCapWidth:10.0
      topCapHeight:0.0] forState:UIControlStateNormal];
[btn setTitle:@"BUTTON" forState:UIControlStateNormal];
[btn setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
[btn.titleLabel setFont:[UIFont boldSystemFontOfSize:14]];

Create a new UIButton of type UIButtonTypeCustom and then set the button skin as the backgroundImage. The horizontal stretchability is due to the stretchableImageWithLeftCapWidth and topCapHeight.

Here is a screenshot from the iPhone simulator showing the button in action:

Files

• gradient.php – the perfect gradient engine
• gradient-button.psd – the photoshop source for the red button image, including the rounded alpha-transparent button and fused red gradients
• btn-red.png – the red button image