Calculating text width including space / kerning between characters using Delphi

Question

I have troubles finding any resources that explain how to calculate the text width of a string with different kearning / space-between characters.

Textwidth can use the font size, font styles etc. but not space between characters? (Or kerning which I believe is very font specific, i.e. gives different pixel values depend on the font since characters since they can "overlap" more or less depending on the kerning/spacing value)

Answer 1

Edit: Recommended reading: Feng Yuan "Windows Graphics Programming"

Example of TextWidth (GetTextExtentPoint32) and more complex method:

var
  Len, w: Integer;
  s: string;
  GR: TGCPResults;
begin
  Canvas.Font.Size := 14;
  s := 'A simple test string';
  Canvas.TextOut(0, 0, s);
  w := Canvas.TextWidth(s);
  Canvas.MoveTo(w, 0);
  Canvas.LineTo(w, 30);

  SetTextCharacterExtra(Canvas.Handle, 5);
  Canvas.TextOut(0, 30, s);
  w := Canvas.TextWidth(s);
  Canvas.MoveTo(w, 30);
  Canvas.LineTo(w, 60);

  SetTextCharacterExtra(Canvas.Handle, 0);
  Len := Length(s);
  GR.lStructSize := sizeOf(GR);
  GetMem(GR.lpOutString, (Len + 1) * sizeOf(Char));
  GR.lpOrder := Nil;
  GetMem(GR.lpDx, (Len + 1) * sizeOf(Integer));
  GetMem(GR.lpCaretPos, (Len + 1) * sizeOf(Integer));
  GR.lpClass := Nil;
  GetMem(GR.lpGlyphs, (Len + 1) * sizeOf(UINT));
  GR.nGlyphs := Len;
  GR.nMaxFit := 0;

  w := GetCharacterPlacement(Canvas.Handle, PwideChar(s), Len, 0, GR,
    GCP_USEKERNING) and $FFFF;
  ExtTextOut(Canvas.Handle, 0, 60, ETO_GLYPH_INDEX, nil, PChar(GR.lpGlyphs),
    GR.nGlyphs, PINteger(GR.lpDx));
  Canvas.MoveTo(w, 60);
  Canvas.LineTo(w, 90);
  // free memory for GR members