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Canvas.TextWidth is not correct!

Problems with exactly scaling a Font:

I tried to fit a text into an Image, so that it starts on the left side and ends on the right side of the Image (as excactly as possible; I know, that
Font.Size is not available for all integer values!).

I used the following simple code:

cvs:=Image.Canvas;
tw:=cvs.TextWidth(ed_Text.Text);
cvs.Font.Size:=30;
while ((tw>=Image.Width) and (cvs.Font.Size>3)) do begin
cvs.Font.Size:=cvs.Font.Size-1;
tw:=cvs.TextWidth(ed_Text.Text);
end; // while ...
cvs.Textout(0,0,s);

(Hereby I will assume, that the Image is high enough to contain
the text, so I do not have to check this here).

The result: the text starts on the left, but does only fill about 80%
of the window leaving blanks on the right side. So it seems to me, that cvs.TextWidth returns a value,
which is too small (I can always find an existing Font.Size, which has a better fit!).

I could solve the problem this way:
tw:=round(1.2 * cvs.TextWidth(ed_Text.Text);
but I think, there must be a more exact way to get the correct
size of the Font on the canvas to ensure exact scaling.

100 Points for a different approach to solve the problem of fitting
the text in width (or also in height), which results in a more exact
fit.

Thanks for any help

Gamba

Igor UL7AAjr

Hi Gamba,

try this sample
-----------
var tw,fs : integer;
S : string;
cnv : TCanvas;
begin
cnv:=Image1.Canvas;
cnv.Font.Size:=6;
S:='sample';
repeat
cnv.Font.Size:=cnv.Font.Size+1;
tw:=cnv.TextWidth(S);
until Image1.Width < tw;
cnv.Font.Size:=cnv.Font.Size-1; // you miss it in your sample
cnv.TextOut(0,0,S);
end;
-----

Igor.

shenqw

s=what?

I think you forgot s:=ed_Text.Text

Igor UL7AAjr

S:='sample';) It's working sample, I check it before public.
----
Igor.

Gamba

ASKER

Thanks, ITugay,
this works o.k., I added the
Height-Part and changed the line
with Font.Size:=Font.Size-1 (see comment). I did not expect it to be
a problem of the missed line!

Do you think, finding the correct Font.Size has to be done iterative
or can it be calculated somehow??

(please add a answer statement and
you will receive the points in any case).

procedure Draw;
var tw,th: integer;
s : string;
cnv : TCanvas;
prevsize : word;
prevw,prevh : integer;
begin
cnv:=Image.Canvas;
cnv.Rectangle(0,0,Image.Width,Image.Height);
cnv.Font.Size:=5;
prevw:=cnv.TextWidth(s);
prevh:=cnv.TextHeight(s);
tw:=prevw;
th:=prevh;
s:=ed_Text.Text;
repeat
if ((tw<>prevw) or (th<>prevh)) and ((Image.Width >= tw) or (Image.Height >= th))
then begin
prevsize:=cnv.Font.Size;
prevw:=tw;
prevh:=th;
end; // if (tw<>prevw) or (th<>prevh)
cnv.Font.Size:=cnv.Font.Size+1;
tw:=cnv.TextWidth(s);
th:=cnv.TextHeight(s);
until ((Image.Width < tw) or (Image.Height < th));
cnv.Font.Size:=prevsize;
(* instead of cnv.Font.Size:=cnv.Font.Size-1, cause cnv.Font.Size-1 has not necessary other
tw and th *)
cnv.TextOut(0,0,S);
end;

Gamba

Igor UL7AAjr

Ok, just a moment...

mullet_attack

If you want an exact fit, use a truetype font. Using the default windows font cause Windows to perform a best-fit calculation of a scaled up/down font.

TextWidth returns the correct width in pixels only for truetype fonts and the pre-defined sizes of system fonts.

ITugay's sample doesn't work properly without a true-type font.

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Igor UL7AAjr

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Gamba

ASKER

Thanks

Gamba