Hello,
in the
VCL somewhere there is sort of a message processing loop.
It calls GetMessage from Windows
API.
If you use a control which internally directly uses a Windows own
control that will fire its events on receiving the apropriate messages.
If you block the main thread it cannot process this message loop pointed above
and thus the
GUI looks non responsive, as messages like WM_PAINT are not handled.
That's the base. More details can be found in Petzold's "Programming Windows"
book. At least in the old versions.
Cheers
TurboMagic