Smooth resizing in a borderless form/window in Delphi

Question

I am trying to resize a borderless form but when I increase the size using the right/bottom side, I get a gap between the border and the old client area that depends of the

Answer 1

Last time I attempted to manually make a top level window that resizes via WM_SYSCOMMAND and mouse drag, whether involving any nested panels or no, I found the problems were not limited only to flicker.

Even with a bare-TForm without a resizeable border, adding my own resizeable border and handling the mouse down and mouse move and mouse up messages directly proved too problematic. I gave up on the code-approach you are showing here, and instead I found two workable approaches:

1. use an approach where I take over the painting of the non-client areas. This is what Google Chrome and many other fully-custom windows do. You still have a nonclient area and it's up to you to paint it and handle the non-client and border paint. In other words, it's not truly borderless, but it could all be a single color, if you wanted it to be. Read this help about WM_NCPAINT messages, to get started.

2. Use a borderless resizeable window that still gets recognized (even without its nonclient area as a resizeable window. Think of a post-it-note-applet. Here is a question I asked a while ago, at the bottom of my question is a fully working demo that provides a smooth flicker free way to have a borderless resizeable window. The underlying technique for the answer was provided by David H.