Todd Anderson

I make things for the web, mobile, desktop and land.

i’m not gonna keep putting the name of the day on the end…

2005 September 21st by todd anderson

Following up on my past two posts.

The prior two experiments were done using a png with a transparent background. i made it, so i know what i wanted… but what if the spritesheet you’re using isn’t in a format without an alpha channel?
I ran a test using a png with a background color to see if i can strip out a specified color and still get the rendered staes i want.
Yes i can- by using the threshold method of the BitmapData class.

the picture above is a screenshot of my test movie that shows the image loaded in the upper-left corner.

To recap: i load an image into a mc, create a BitmapData instance and BitmapData.draw(mc) to capture the bitmap. Then i (aside from here) delete the mc, pass the BitmapData instance onto a “dissector” and render each state dependant on user action.
In order to remove the offending color (in this case all pixels with a value of 0×00333333), run the following before passing the BitmapData instance on:

// — where  

//              __bmp is my BitmapData instance,  

//              __threshold = 0×00333333,  

//              w and h are the dimesions of the loaded image  

// –  

private function applyThreshold(w:Number, h:height)  


    __bmp.threshold(__bmp, new Rectangle(0, 0, w, h), new Point(0, 0), “==”, __threshold, 0xffff00, 0xffffff, false);  


I kept the dropShadow in there to see if it still applied afterward, and lo and behold! excellent.
One thought… for some reason when i set the color and mask arguments both to white, it didn’t mask- don’t know why, but i didn’t investigate too hard.
Two thought… if my states held that same offending color (say in the eyes), it will remove it – i’ll have to work on that.

Posted in Flash, Flash8.