How to draw a selected text in win32 using only gdi call ?

Question

I tried to draw a selected text using two TextOut call and TA_UPDATECP flag but when I move the selected area, the characters are moving a bit.

Does someone know the correct way to do that ?

Answer 1

According to the MSDN documentation, when you have set the TA_UPDATECP flag using SetTextAlign(), TextOut() ignores its position parameters in favor of the device context's current position. Without seeing your code, I suspect that your drawing algorithm calls TextOut() with a current position that differs slightly based on the selection.

As a debugging strategy, you can call GetCurrentPositionEx() just before you call TextOut() to obtain the current position and make sure it matches your expectation for where the text should be drawn.

Answer 2

I believe that antialiasing and ClearType can draw text at fractional pixel positions. If you draw a string of text, and then try to redraw a portion of the middle, there might not be a way for you to draw text starting at exactly the same position as those characters in the middle. The trick seems to be to redraw the entire string, but with a clipping region for the selected text.

This tutorial on writing a Win32 text editor goes into quite some detail on how to draw selected text.