No displaying a bitmap using WinApi/GDI
lazarus / 39-Graphics

----------------------------------------------------------------------
ADMGNS · 2024-08-13 22:43

Hello

I am traying to display a bitmap using WinApi/GDI, but no displaying..
C and Pascal source codes are identical (see attachments).. C one
works, but pascal one doesn't..

What is the wrong thing?? Thanks

----------------------------------------------------------------------
440bx · 2024-08-14 00:29

The C version declares some of the variables as "static" which means,
the variables retain their value in subsequent calls to the window
procedure.  In your Pascal code, the same variables are NOT static,
just plain local variables, this causes them to lose their value.

Specifically, the value of the bitmap handle obtained in the WM_CREATE
is lost when WM_CREATE ends, therefore the WM_PAINT is using some
garbage that is occupying the bitmap handle when the WM_PAINT is
processed.

Solution: ensure the variables declared as "static" in the C code are
either global variables in your code or writable type constants (which
is what "static" is in FPC.)

HTH.

----------------------------------------------------------------------
440bx · 2024-08-14 00:36

Also, if you're interested in programming directly to the Windows API,
the following examples may be useful to you:

https://forum.lazarus.freepascal.org/index.php/topic,53791.0.html

Among others, there is an example that loads a bitmap and displays it
in the window.

HTH.

----------------------------------------------------------------------
ADMGNS · 2024-08-14 02:59

thanks for your replies.. SOLVED.