How to load/draw out visible rectangle of webview?

My question is described below:

I am implementing an eReader's app, which sets pagination by css3-multi columns.

Suppose pageWidth is 680.

First, when uiwebView finishes loading, x of scrollview position is 0.

If con开发者_StackOverflow社区troller is running next page, x of scrollview position+=680.

Similarly, x of scrollview position-=680, when controller is running pervious page.

But it runs slow if there are any images on the pervious or next page.

It seems that images which "out visible rectangle of webview" didn't start to load until images will become to visible...

How to load/draw out visible rectangle of webview?

Would it be possible for me to change the size of visible rectangle of webview?

I'm looking forward to your further explanation, thank you in advance!

the width of the layout needs to be set to at least 2X the inner width of the window's width for the columns to render (the width will grow as needed to adapt to larget text)!!