Home > CSS, iScroll, JavaScript, Object Pascal, OP4JS, Smart Mobile Studio > For those about to scroll, we salute you

For those about to scroll, we salute you

Came up with a better solution to the scrolling problem for Smart Mobile Studio. While I hate having to write code for Internet Explorer, it is nice to have a system that works everywhere. But that means more abstraction and “drivers” type classes.

The scrolling model

TW3Scrollbox and it’s variation(s) implement different types of scrolling. TW3Scrollbox has a very fast non-momentum scroll, making it perfect for displaying detailed information. But it would be nice if we could choose right?

The model I have come up with is super simple, especially in the upcoming RTL where we finally have non-visual components. I give you – TW3ScrollController


In the present model, TW3Scrollbox deals with scrolling directly. Actually the scrolling is implemented in the TW3ScrollContent control, mapping touch and mouse events directly. This turned out to be a remarkably fast way of moving things around. I really did not expect IE to keep up, but it’s perfectly pristine!

In the momentum-scroll example I posted, control of scrolling is handled by the container rather than content. This is very fast on webkit, and I also tried it on Microsoft mobile and Windows 10 mobile – and it’s very fast there. But for some reason the desktop Internet Explorer is slow and the content jitters a bit.

The culprit is not my code or approach, it’s actually something else. Internet Explorer and Edge are the only browsers that implements OnReSize() events. No other browser has this. In the SMS RTL we have to manually figure out when to call ReSize (based on the BeginUpdate, AddControlState, EndUpdate methods).

In the momentum scroller I use SetBounds() to keep the content within the horizontal bounds of the control. This causes an extra call to Resize every time the content moves even a pixel (even though it shouldnt, because the size doesnt change). So yeah, fixing that will make all the difference. I’m going to nail this thing once and for all, just like I did with font measurements way back.


But isolating the code that actually deals with scrolling in separate, non visual components that you can attach to the TW3ScrollBox makes sense. Rather than hardcoding everything into a huge, spaghetti monster unit — we can now isolate different scroll methods in their own units (keeping those bytes down).
Normal per-pixel scrolling, momentum scrolling, CSS3 animation based scrolling, tween based (cpu) scrolling. It gives us some options – and allows you to implement your own variations if you find mine lacking.

I’m also giving the browser driver a much deserved overhaul. Getting the browser type and version info should be easy (and humanly readable). And since you may want to pick different scroll methods depending on the browser type — being able to check if your running on Edge for the desktop, or IE on a mobile device… well, it should be there. End of story.


I really want iScroll to be the standard scroll library for Smart Mobile Studio, but since people feel it’s hard to use and adapt to — I may end up doing the unthinkable and re-write it in object pascal from scratch. But iScroll5 really is so much better. It has been developed and tested on a plethora of devices for six years now.

It even does things the built-in browser scrolling (for the browsers that allows this, yeah im looking at you Safari!) doesn’t deal with.

But I have enough on my plate right now, so iScroll porting will have to wait.

  1. June 11, 2016 at 4:05 pm

    I like this scrolling model, don’t forget to include mouse wheel handling (for desktop browsers).

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