making more testing on this
1. capture single line other than top most one, will get a normal line but differ to that position in fullshot.
2. font in fullshot looks smaller.
3. cannot use it for copying full or part of bitmap. i had tested with createcompitableDC and selectobject like C
4. tbitmap.canvas.draw(0,0,other bitmap) will not copy too.
5. set a timer to 30ms for drawing a captured shot in TImage, my 6 cores Intel CPU runs at 14% usage, almost 100% of 1 core, amazing.........
all above testing did just for my old delphi vcl code port to FPC, but now, look Difficult to do.
for delphi vcl code, item 1,2,3 can use bitblt with bitmap.canvas.lock to do.
item 5 just consume 1%