Text zooming similar to 'The Economist' or 'Apple iBooks'

Can anyone tell me how could I get the similar zooming like 'The Economist' or 'Apple iBooks'. What may be the technique used to get that performance and look and feel.

I have tried usin开发者_C百科g the html+webview, javascript to get the zooming effect but it is not perfect. :(

Do any one tell me how could we get the same appearance?