[fpc-pascal] How does TFPImageCanvas draw TextOut?
dle3ab at angelbase.com
Sun Mar 1 02:04:17 CET 2009
I've started with the fontdraw example at the bottom of
Somewhere in the middle, there's a call to ImgCanvas.TextOut, which
seems to work just fine -- the png file has the text, and if I create a
cracker class I can call TFPImageCanvasCracker.GetColor and find where
the text has been drawn, without the writer, memory stream, or file
stream. I don't understand how it works, though.
In the fontdraw program,
var ImgCanvas: TFPImageCanvas;
In unit fpimgcanv,
type TFPImageCanvas = class (TFPPixelCanvas)
but it doesn't have a TextOut method.
In unit fppixlcanv,
type TFPPixelCanvas = class (TFPCustomCanvas)
and it doesn't have a TextOut method, either.
and in unit fpcanvas,
type TFPCustomCanvas = class(TPersistent)
public procedure TextOut (x,y:integer;text:string);
Okay, so I see that in the fontdraw example program, ImgCanvas inherits
TextOut from TFPCustomCanvas; and it's not overridden in TFPPixelCanvas
TFPCustomCanvas.TextOut simply calls DoTextOut, however
TFPCustomCanvas.DoTextOut is virtual; abstract;
In TFPPixelCanvas, I see protected procedure DoTextOut
However, the procedure only makes a call to "NotImplemented;"
And TFPImageCanvas does not override DoTextOut, either.
So what on earth is going on here? I don't see any place where a
procedure is being called that actually draws the text.
I do see that in ftfont, a DrawText procedure exists -- and it seems
pretty clear that that's the procedure that's actually drawing the
text. But how is it being called?
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