Graphics - Working with TCanvas
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Revision as of 16:51, 26 May 2018 by Mathias (talk | contribs) (→Drawing text with sharp edges (non antialiased))
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Using the default GUI font
This can be done with the following simple code:
SelectObject(Canvas.Handle, GetStockObject(DEFAULT_GUI_FONT));
Drawing a text limited on the width
Use the DrawText routine, first with DT_CALCRECT and then without it.
// First calculate the text size then draw it
TextBox := Rect(0, currentPos.Y, Width, High(Integer));
DrawText(ACanvas.Handle, PChar(Text), Length(Text),
TextBox, DT_WORDBREAK or DT_INTERNAL or DT_CALCRECT);
DrawText(ACanvas.Handle, PChar(Text), Length(Text),
TextBox, DT_WORDBREAK or DT_INTERNAL);
Drawing text with sharp edges (non antialiased)
Some widgetsets support this via
Canvas.Font.Quality := fqNonAntialiased;
Some widgetsets like the gtk2 do not support this and always paint antialiased. Here is a simple procedure to draw text with sharp edges under gtk2. It does not consider all cases, but it should give an idea:
procedure PaintAliased(Canvas: TCanvas; x, y: integer; const TheText: string);
var
w, h, dx, dy: Integer;
IntfImg: TLazIntfImage;
Img: TBitmap;
col: TFPColor;
FontColor, c: TColor;
begin
w := 0;
h := 0;
Canvas.GetTextSize(TheText, w, h);
if (w <= 0) or (h <= 0) then exit;
Img := TBitmap.Create;
IntfImg := nil;
try
// paint text to a bitmap
Img.Masked := true;
Img.SetSize(w,h);
Img.Canvas.Brush.Style := bsSolid;
Img.Canvas.Brush.Color := clWhite;
Img.Canvas.FillRect(0, 0, w, h);
Img.Canvas.Font := Canvas.Font;
Img.Canvas.TextOut(0, 0, TheText);
// get memory image
IntfImg := Img.CreateIntfImage;
// replace gray pixels
FontColor := ColorToRGB(Canvas.Font.Color);
for dy := 0 to h - 1 do begin
for dx := 0 to w - 1 do begin
col := IntfImg.Colors[dx, dy];
c := FPColorToTColor(col);
if c <> FontColor then
IntfImg.Colors[dx, dy] := colTransparent;
end;
end;
// create bitmap
Img.LoadFromIntfImage(IntfImg);
// paint
Canvas.Draw(x, y, Img);
finally
IntfImg.Free;
Img.Free;
end;
end;