Why TextOut in Canvas connects Box-Drawing Characters with a gap when I print them not sequentially in one statement?

Question

I use the fonts "Consolas" and/or "Courier New" in a project to draw an MS-DOS-looking environment. In this project if I use TextOut (of the TCanvas) to print for Box Drawing characters sequentially in one statement, everything is fine, for example it prints "────────" but if I address each character to print them separately, there would be a gap between each character, something like this: "-----------". Here is an example for you to test it manually:

  ...

  Canvas.Font.Size := 12;

  w := Canvas.TextWidth('╬');
  h := Canvas.TextHeight('╬');

  Canvas.TextOut(100, 100, '╬╬');

  Canvas.TextOut(100, 100 + h, '╬');
  Canvas.TextOut(100 + w, 100 + h, '╬');

  Canvas.TextOut(100, 100 + h * 2, '╬');
  Canvas.TextOut(100 + w, 100 + h * 2, '╬');

The output is:

As you can see, vertically they are connected fine but horizontally there is a gap.

How can I fix it? Note that I draw what I want in an array, and then a procedure prints the array as follows:

  th := Canvas.TextHeight('A');
  tw := Canvas.TextWidth('A');
  for i := 0 to MaxWidth - 1 do
    for j := 0 to MaxHeight - 1 do
    begin
      Canvas.Brush.Color := fChars[i, j].BGColor;
      Canvas.Font.Color := fChars[i, j].FGColor;
      Canvas.TextOut(i * tw, j * th, fChars[i, j].Character);
    end;

Does this answer your question? [What are the implications of using Canvas.TextOut?](https://stackoverflow.com/questions/31968771/what-are-the-implications-of-using-canvas-textout) — whosrdaddy, Jul 13 '20 at 22:19

whosrdaddy · Accepted Answer · 2020-07-13T22:20:37.553

If you use DrawText() instead of Canvas.TextOut() it works. The reason is explained in this SO answer. It is related to character kerning applied by the different windows API's on certain fonts.

here is a full working example:

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls;

type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
        FFont: TFont;
  public
    { Public declarations }
  end;

type TMyChar = record
  BGColor : TColor;
  FGColor : TColor;
  Character : Char;
end;

const
  FWidth : Integer = 9;
  FHeight : Integer = 9;

var
  Form1: TForm1;
  Fchars : Array[0..9,0..9] of TMyChar;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);

var
 i,j : Integer;

begin
  Canvas.Font.Size := 12;
  Canvas.Font.Name := 'Courier New';
  for i := 0 to FWidth do
    for j := 0 to FHeight do
    begin
     FChars[i,j].Character:= '╬';
     FChars[i,j].BGColor := clBlue;
     FChars[i,j].FGColor := clYellow;
    end;

end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
 FFont.Free;
end;

procedure TForm1.FormPaint(Sender: TObject);
var w,h,i,j: Integer;
    FRect : TRect;
begin
  h := Canvas.TextHeight('A');
  w := Canvas.TextWidth('A');
  for i := 0 to FWidth do
    for j := 0 to FHeight do
    begin
      Canvas.Brush.Color := fChars[i, j].BGColor;
      Canvas.Font.Color := fChars[i, j].FGColor;
//      Canvas.TextOut(i * w, j * h, fChars[i, j].Character);
      FRect := Rect(i * w, j * h, i * w + w, j * h + h);
      DrawText(Canvas.Handle, (fChars[i, j].Character), 2, FRect, DT_LEFT);
    end;
  end;

end.

You don't need to abandon `TCanvas` if you don't want to: you can use its `TextRect` method. — Andreas Rejbrand, Jul 13 '20 at 23:13
Thanks. This works although it is much slower when the array is 150 x 50. — M Ahmadzadeh, Jul 15 '20 at 20:13

Why TextOut in Canvas connects Box-Drawing Characters with a gap when I print them not sequentially in one statement?

1 Answers1