[圖形] 如何做到刮刮樂的效果

http://stackoverflow.com/questions/5848722/android-scratch-card-app

https://market.android.com/details?id=com.wxj.fingerpaint4kid&hl=zh_TW

Market上已經有的ap
https://market.android.com/details?id=ginlemon.scratchdemo&feature=search_result

Jquery網頁版本:
http://www.senamion.com/blog/jScratchcard.html

相關討論
http://stackoverflow.com/questions/3007750/create-masking-effect-over-a-view