Mega Code Archive
Drawing in scale without using windows mapping modes
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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;
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