Question

I have a carbon application with a list view data browser and vertical scrolling. When the list is long (hundreds of items), rapid scrolling through the window produces blurred, sometimes “smeared” text:

Other artifacts can also occur, such as clipped or overlapping lines. Sometimes the entire contents are nothing but a vortex-like smear. Clicking any item causes a normal repaint of the ListView contents. Here is how Interface Builder sees the ListView:

I am building against MacOSX10.5.sdk using Xcode 3.2.6. Building and testing is under 10.6. I am not doing any special handling of scroll events. I have only defined DataBrowserCallbacks for itemDataCallback, itemNotificationCallback, and itemCompareCallback.

My question is: what could possibly cause this?

Answer 1

I figured it out, so here is the answer for posterity:

It turns out that the problem always and only occurs when the list view data browser is positioned at a non-integer horizontal offset.

HIViewSetFrame() takes an HIRect argument which uses float types for origin and size. When the parent frame is resized such that the origin of the browser falls on a non-integer origin.x, the graphics errors are triggered. It does not matter whether or not the vertical offset or either size dimension is non-integral.

The solution is to ensure that browsers which are moved when the window resizes have their x value rounded off:

frame.origin.x = roundf(frame.origin.x);

It does not appear that any other controls have any problems with non-integer origins.