如何将Skia4Delphi中TSkPaintBox的画布保存到文件并转为TBitmap？

核心前提 #

要导出签名，你需要先维护一个ISKPath对象记录用户的绘制路径（因为TSkPaintBox的画布是临时的，每次重绘都会刷新，无法直接从其Canvas提取内容）。先在窗体类中声明相关变量：

private
  FSignaturePath: ISKPath;
  FIsDrawing: Boolean;

然后在TSkPaintBox的鼠标事件中记录路径，在OnPaint事件中绘制：

procedure TForm1.SkPaintBox1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Button = mbLeft then
  begin
    FIsDrawing := True;
    FSignaturePath := TSKPath.Create;
    FSignaturePath.MoveTo(X, Y);
  end;
end;

procedure TForm1.SkPaintBox1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if FIsDrawing then
    FSignaturePath.LineTo(X, Y);
  SkPaintBox1.Repaint;
end;

procedure TForm1.SkPaintBox1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Button = mbLeft then
    FIsDrawing := False;
end;

procedure TForm1.SkPaintBox1Paint(Sender: TObject; const ACanvas: ISKCanvas);
var
  LPaint: ISKPaint;
begin
  LPaint := TSKPaint.Create;
  LPaint.Style := TSKPaintStyle.Stroke;
  LPaint.Color := TSKColors.Black;
  LPaint.StrokeWidth := 2;
  ACanvas.DrawPath(FSignaturePath, LPaint);
end;

导出为TBitmap #

通过创建与TSkPaintBox尺寸一致的SKBitmap，将保存的签名路径绘制到该Bitmap，再转换为VCL的TBitmap：

function TForm1.SignatureToBitmap: TBitmap;
var
  LSKBitmap: ISKBitmap;
  LSKCanvas: ISKCanvas;
  LPaint: ISKPaint;
begin
  Result := TBitmap.Create;
  try
    // 创建对应尺寸的SKBitmap，背景设为白色
    LSKBitmap := TSKBitmap.Create(SkPaintBox1.Width, SkPaintBox1.Height, TSKColorType.RGBA8888);
    LSKBitmap.Erase(TSKColors.White);

    // 绘制签名路径
    LSKCanvas := TSKCanvas.Create(LSKBitmap);
    LPaint := TSKPaint.Create;
    LPaint.Style := TSKPaintStyle.Stroke;
    LPaint.Color := TSKColors.Black;
    LPaint.StrokeWidth := 2;
    LSKCanvas.DrawPath(FSignaturePath, LPaint);

    // 转换为VCL TBitmap
    LSKBitmap.ToBitmap(Result);
  except
    Result.Free;
    raise;
  end;
end;

调用示例：

var
  LBitmap: TBitmap;
begin
  LBitmap := SignatureToBitmap;
  try
    // 使用LBitmap，比如赋值给Image控件
    Image1.Picture.Assign(LBitmap);
  finally
    LBitmap.Free;
  end;
end;

保存到文件 #

直接利用SKBitmap的EncodeToFile方法，将签名保存为PNG/JPG等格式：

procedure TForm1.SaveSignatureToFile(const AFileName: string);
var
  LSKBitmap: ISKBitmap;
  LSKCanvas: ISKCanvas;
  LPaint: ISKPaint;
begin
  LSKBitmap := TSKBitmap.Create(SkPaintBox1.Width, SkPaintBox1.Height, TSKColorType.RGBA8888);
  LSKBitmap.Erase(TSKColors.White);

  LSKCanvas := TSKCanvas.Create(LSKBitmap);
  LPaint := TSKPaint.Create;
  LPaint.Style := TSKPaintStyle.Stroke;
  LPaint.Color := TSKColors.Black;
  LPaint.StrokeWidth := 2;
  LSKCanvas.DrawPath(FSignaturePath, LPaint);

  // 保存为PNG，可替换为TSKEncodedImageFormat.Jpeg等格式
  LSKBitmap.EncodeToFile(AFileName, TSKEncodedImageFormat.Png);
end;

调用示例：

SaveSignatureToFile('C:\temp\signature.png');

内容的提问来源于stack exchange，提问作者Richard Shuck