Creating PNG Images with Rounded Corners

I have been working with the image functions in ColdFusion 8 and trying to figure out how to create rounded corners using an existing image.

First let me point out there are some impressive professional products available that can perform this feat, such as Image Effects by Foundeo Inc. Obviously it is more robust and better suited to handling high resolution, high quality images, than the technique described here ;) As my image needs were more basic, I decided to investigate if this were possible using only ColdFusion's built in image functions.

Searching the documentation I found the ImageDrawRoundRect function. It looked promising but it appears to work only for drawing new shapes. What I needed was a way to clip the drawing area of an existing shape. Not having found a suitable combination of CF image functions yet, I decided to try my hand at creating a function that used java directly.

Clipping

My first inclination was to try clipping. Using the same dimensions as the original image, I created a BufferedImage that supports transparency.

<cfscript>
Local.BufferedImage = createObject("java", "java.awt.image.BufferedImage");
Local.destImage = Local.BufferedImage.init(
javacast("int", Local.width),
javacast("int", Local.height),
Local.BufferedImage.TYPE_INT_ARGB
);
</cfscript>

I then used a rounded rectangle to define the clipping area, so anything outside the bounds of the rectangle would appear transparent.

<cfscript>
Local.graphics = Local.destImage.createGraphics();
Local.RoundRectangle2D = createObject("java", "java.awt.geom.RoundRectangle2D$Double");
Local.rounded = Local.RoundRectangle2D.init( javacast("double", 0),
javacast("double", 0),
javacast("double", Local.width),
javacast("double", Local.height),
javacast("double", arguments.arcWidth),
javacast("double", arguments.arcHeight)
);
Local.graphics.setClip( Local.rounded );
</cfscript>

Finally I drew the original image onto the new BufferedImage. Then passed the BufferedImage into the ImageNew() function to return a CF compatible image object.

<cfscript>
Local.graphics.drawImage( Local.sourceImage,
javacast("int", 0),
javacast("int", 0),
javacast("null", "")
);
Local.graphics.dispose();
</cfscript>

<cfreturn ImageNew( Local.destImage )>

As you can see it did work. But if you look closely at the image on the right, the rounded edges appear ragged. At least on the windows o/s.

Images © Nicolas Raymond

If at first you don't succeed

Next I tried a tip from the sun.com forums. It suggested using a mask to do the equivalent of clipping, but with better blending of the edges. So this time I used anti-aliasing to draw the rounded rectangle shape first.

Update: This article gives a good explanation of why the mask technique works, as it involves more than just using the anti-aliasing hint.
http://weblogs.java.net/blog/campbell/archive/2006/07/java_2d_tricker.html

<cfscript>
// cfSearching: use anti-aliasing for smoother edges
Local.RenderingHints = createObject("java", "java.awt.RenderingHints");
Local.graphics.setRenderingHint( Local.RenderingHints.KEY_ANTIALIASING,
Local.RenderingHints.VALUE_ANTIALIAS_ON
);
// cfSearching: create a rounded rectangle mask
Local.graphics.setColor( Local.Color.WHITE );
Local.graphics.fillRoundRect(javacast("double", 0),
javacast("double", 0),
javacast("double", Local.width),
javacast("double", Local.height),
javacast("double", arguments.arcWidth),
javacast("double", arguments.arcHeight)
);
</cfscript>

Then used a Source-in AlphaComposite to draw the original image over the rectangle mask. Again the end result being everything outside the rectangle area appears transparent. If you are not familiar with compositing rules, take a peek at one of the sun.com tutorials. The image examples clearly demonstrate the effect of the different AlphaComposite rules.

<cfscript>
// cfSeaching: draw the source image onto the mask
Local.graphics.setComposite( Local.AlphaComposite.SrcIn );
Local.graphics.drawImage( Local.sourceImage,
javacast("int", 0),
javacast("int", 0),
javacast("null", "")
);
Local.graphics.dispose();
</cfscript>

As you can see the resulting corners are much smoother this time.

Images © Nicolas Raymond

Conclusion

Now there is obviously much more to handling graphics than I covered here. But hopefully this simple technique demonstrates a few of the things you can do with BufferedImages. As always, comments/corrections/suggestions are welcome. Enjoy!


Clipping Example (Ragged Edges)

<h1>Rounded Corners (Clip) Example</h1>

<cfset fullPathToSourceImage = ExpandPath("testImage3.jpg")>
<!--- display original image --->
<cfoutput>
<img src="#GetFileFromPath(fullPathToSourceImage)#"><br><br>
</cfoutput>

<!--- display new image with rounded corners (arc 50 x 50) --->
<cfset roundedImage = roundedCornersClip( fullPathToSourceImage, 50, 50 )>
<cfimage source="#roundedImage#" action="WriteToBrowser" format="png">


<cffunction name="roundedCornersClip" returntype="any" access="public" output="false">
<cfargument name="source" type="string" required="true" hint="full path to source image">
<cfargument name="arcWidth" type="numeric" required="true" hint="horizontal diameter of arc">
<cfargument name="arcHeight" type="numeric" required="true" hint="vertical diameter of arc">
<cfset var Local = structNew()>

<cfscript>
Local.sourceImage = ImageGetBufferedImage(ImageNew(arguments.source));
Local.width  = Local.sourceImage.getWidth();
Local.height = Local.sourceImage.getHeight();

Local.BufferedImage = createObject("java", "java.awt.image.BufferedImage");
Local.destImage = Local.BufferedImage.init(
javacast("int", Local.width),
javacast("int", Local.height),
Local.BufferedImage.TYPE_INT_ARGB
);

Local.graphics = Local.destImage.createGraphics();
Local.RoundRectangle2D = createObject("java", "java.awt.geom.RoundRectangle2D$Double");
Local.rounded = Local.RoundRectangle2D.init( javacast("double", 0),
javacast("double", 0),
javacast("double", Local.width),
javacast("double", Local.height),
javacast("double", arguments.arcWidth),
javacast("double", arguments.arcHeight)
);

Local.graphics.setClip( Local.rounded );  
Local.graphics.drawImage( Local.sourceImage,
javacast("int", 0),
javacast("int", 0),
javacast("null", "")
);
Local.graphics.dispose();
</cfscript>

<cfreturn ImageNew( Local.destImage )>
</cffunction>

Mask Example (Smoother Edges)

<h1>Rounded Corners (Mask) Example</h1>

<cfset fullPathToSourceImage = ExpandPath("testImage3.jpg")>

<!--- display original image --->
<cfoutput>
<img src="#GetFileFromPath(fullPathToSourceImage)#"><br><br>
</cfoutput>

<!--- display new image with rounded corners (arc 50 x 50) --->
<cfset roundedImage = roundedCornersMask( fullPathToSourceImage, 50, 50 )>
<cfimage source="#roundedImage#" action="WriteToBrowser" format="png">

<cffunction name="roundedCornersMask" returntype="any" access="public" output="false">
<cfargument name="source" type="string" required="true" hint="full path to source image">
<cfargument name="arcWidth" type="numeric" required="true" hint="horizontal diameter of the rounded corners">
<cfargument name="arcHeight" type="numeric" required="true" hint="vertical diameter of the rounded corners">

<cfscript>
var Local = structNew();

// cfSearching: create required java objects
Local.Color = createObject("java", "java.awt.Color");
Local.AlphaComposite = createObject("java", "java.awt.AlphaComposite");

Local.sourceImage = ImageGetBufferedImage(ImageNew(arguments.source));
Local.width  = Local.sourceImage.getWidth();
Local.height = Local.sourceImage.getHeight();

// cfSearching: create a bufferedImage to hold the mask
Local.BufferedImage = createObject("java", "java.awt.image.BufferedImage");
Local.Mask = Local.BufferedImage.init( javacast("int", Local.width),
javacast("int", Local.height),
Local.BufferedImage.TYPE_INT_ARGB
);
Local.graphics = Local.Mask.createGraphics();

// cfSearching: use anti-aliasing for smoother edges
Local.RenderingHints = createObject("java", "java.awt.RenderingHints");
Local.graphics.setRenderingHint( Local.RenderingHints.KEY_ANTIALIASING,
Local.RenderingHints.VALUE_ANTIALIAS_ON
);
// cfSearching: create a rounded rectangle mask
Local.graphics.setColor( Local.Color.WHITE );
Local.graphics.fillRoundRect(javacast("double", 0),
javacast("double", 0),
javacast("double", Local.width),
javacast("double", Local.height),
javacast("double", arguments.arcWidth),
javacast("double", arguments.arcHeight)
);

// cfSeaching: draw the source image onto the mask
Local.graphics.setComposite( Local.AlphaComposite.SrcIn );
Local.graphics.drawImage( Local.sourceImage,
javacast("int", 0),
javacast("int", 0),
javacast("null", "")
);
Local.graphics.dispose();
</cfscript>

<cfreturn ImageNew(Local.Mask)>
</cffunction>