Главная страница | назад





Article #17736: Drawing in scale without using Windows Mapping Modes?

 Question and Answer Database

FAQ2736D.txt   Drawing in scale without using Windows Mapping Modes?
Category   :Windows API
Platform    :All
Product    :All 32 bit  

Question:
How can I draw in scale without using Windows Mapping Modes?


Answer:
You will need to use the Windows API function GetDeviceCaps() to
retrieve the "logical" number of pixels per inch for the display in
both the X and y directions, and multiply your coordinates by the
returned values. Screen measurements are based on a concept of
"Logical Pixels" and may not always reflect a true measurement.
Printers should give satisfactory results when measurement are
compared against a ruler. When printing, delete the lines for GetDc()
and ReleaseDc() and simply pass Printer.Canvas.Handle to the
GetDeviceCaps() function.

Example:

procedure TForm1.Button1Click(Sender: TObject);
var
  dc : hdc;
  InchX : integer;
  InchY : integer;
begin
  dc := GetDc(0);
  InchX := GetDeviceCaps(dc, LOGPIXELSX);
  InchY := GetDeviceCaps(dc, LOGPIXELSY);
  ReleaseDC(0, dc);
  Form1.Canvas.Rectangle(Round(0 * InchX),
                         Round(0 * InchY),
                         Round(1.5 * InchX),
                         Round(1.5 * InchY));
end;


7/16/98 4:31:28 PM
 

Last Modified: 01-SEP-99