Calculating size of text before drawing to a canvas

问题

I'm using Delphi 7. I'm more than familiar with using a canvas and drawing text to a canvas, and also using TCanvas.TextHeight etc. The problem arises when I want to implement Word Wrap. Not only do I need the best way to draw text to a canvas and have it automatically wrap to a given width constraint, but I also need to know how high (or how many lines) it will be after it's wrapped. I need to prepare another image before I draw the text, an image which needs to be just big enough to place the wrapped text. This is an attempt to replicate how an iPhone displays SMS messages, with a baloon on either side of the screen in a variable height scrolling box (TScrollingWinControl is my base).

回答1:

Use the (almost) omnipotent DrawText function using an initial rectangle, and the flags DT_WORDBREAK (meaning that the string should be word-wrapped) and DT_CALCRECT:

procedure TForm1.FormPaint(Sender: TObject); const   S = 'This is a sample text, I think, is it not?'; var   r: TRect; begin   r := Rect(10, 10, 60, 60);   DrawText(Canvas.Handle,     PChar(S),     Length(S),     r,     DT_LEFT or DT_WORDBREAK or DT_CALCRECT);    DrawText(Canvas.Handle,     PChar(S),     Length(S),     r,     DT_LEFT or DT_WORDBREAK); end; 

Due to the flag DT_CALCRECT, the first DrawText will not draw anything, but only alter the height of r so that it can contain the entire string S (or reduce the width of r if S happens to fit on a single line; in addition, if S contains a word that does not fit on a single line, the width of r will be increased). Then you can do whatever you wish with r, and then you can draw the string for real.

Try this, for example:

procedure TForm1.FormPaint(Sender: TObject); const   S: array[0..3] of string = ('Hi! How are you?',     'I am fine, thanks. How are you? How are your kids?',     'Fine!',     'Glad to hear that!');   Colors: array[boolean] of TColor = (clMoneyGreen, clSkyBlue);   Aligns: array[boolean] of integer = (DT_RIGHT, DT_LEFT); var   i, y, MaxWidth, RectWidth: integer;   r, r2: TRect; begin    y := 10;   MaxWidth := ClientWidth div 2;    for i := low(S) to high(S) do   begin      Canvas.Brush.Color := Colors[Odd(i)];      r := Rect(10, y, MaxWidth, 16);     DrawText(Canvas.Handle,       PChar(S[i]),       Length(S[i]),       r,       Aligns[Odd(i)] or DT_WORDBREAK or DT_CALCRECT);      if not Odd(i) then     begin       RectWidth := r.Right - r.Left;       r.Right := ClientWidth - 10;       r.Left := r.Right - RectWidth;     end;      r2 := Rect(r.Left - 4, r.Top - 4, r.Right + 4, r.Bottom + 4);     Canvas.RoundRect(r2, 5, 5);      DrawText(Canvas.Handle,       PChar(S[i]),       Length(S[i]),       r,       Aligns[Odd(i)] or DT_WORDBREAK);      y := r.Bottom + 10;    end;  end;  procedure TForm1.FormResize(Sender: TObject); begin   Invalidate; end; 

来源：https://stackoverflow.com/questions/7719025/calculating-size-of-text-before-drawing-to-a-canvas