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