Question and Answer Database
FAQ2774D.txt Non VCL Bitmap buffering
Category :Windows API
Platform :All
Product :All 32 bit
Question:
How do I create a non VCL memory display context and bitmap for
additional drawing performance?
Answer:
You will need to use low level Windows API functions.
Example:
procedure TForm1.Button1Click(Sender: TObject);
var
dc : hdc;
MemDc : hdc;
MemBitmap : hBitmap;
OldMemBitmap : hBitmap;
begin
{Get the handle to the screen's dc}
dc := GetDc(0);
{Create and retrieve a handle to a memory dc based on the screen}
MemDc := CreateCompatibleDc(dc);
{Create a bitmap that is compatible with the display.}
{Note: if you pass "MemDc" to CreateCompatibleBitmap()}
{instead of "dc", you will get a monochrome bitmap!}
MemBitmap := CreateCompatibleBitmap(dc, 100, 100);
{Release the screen dc}
ReleaseDc(0, dc);
{Select the bitmap surface into the MemDc}
{remembering the default bitmap}
OldMemBitmap := SelectObject(MemDc, MemBitmap);
{Draw on the MemoryDc}
PatBlt(MemDc, 0, 0, 100, 100, WHITENESS);
Ellipse(MemDc, 0, 0, 100, 100);
{Copy the MemDc to the Form Canvas}
BitBlt(Form1.Canvas.Handle,
100, 100,
100, 100,
MemDc,
0, 0,
SRCCOPY);
{Select the default bitmap back into the memory dc}
SelectObject(MemDc, OldMemBitmap);
{Note: You can now use the memory bitmap handle with}
{functions such as GetDiBits()}
{Delete the Memory Bitmap}
DeleteObject(MemBitmap);
{Delete the MemoryDc}
DeleteDc(MemDc);
end;
7/16/98 4:31:28 PM
Last Modified: 01-SEP-99