在Delphi中缩放画布区域

Question

我在Delphi中制作看起来像Paint的东西。我找到了如何制作缩放功能：

procedure SetCanvasZoomFactor(Canvas: TCanvas; AZoomFactor: Integer);
var
  i: Integer;
begin
  if AZoomFactor = 100 then
    SetMapMode(Canvas.Handle, MM_TEXT)
  else
  begin
    SetMapMode(Canvas.Handle, MM_ISOTROPIC);
    SetWindowExtEx(Canvas.Handle, AZoomFactor, AZoomFactor, nil);
    SetViewportExtEx(Canvas.Handle, 100, 100, nil);
  end;
end;



procedure TMainForm.btnZoomPlusClick(Sender: TObject);
var
  bitmap: TBitmap;
begin 

  bitmap := TBitmap.Create;
  if(zoomVal < 1000) then
      zoomVal:=zoomVal+zoomConst; //zoomVal = 100 by default; zoomConst = 150;
  try
    bitmap.Assign(MainForm.imgMain.Picture.Bitmap);
    SetCanvasZoomFactor(bitmap.Canvas, zoomVal);
    Canvas.Draw(MainForm.imgMain.Left,MainForm.imgMain.Top, bitmap); 
  finally
    bitmap.Free
  end;
end;

但问题是 - 它只放大图像的左上区域。

实施例 缩放前： 放大后：

我希望能够在缩放后移动所有图片区域。我该怎么做？

Answer 1

您可以为每个DC使用SetWorldTransform。 示例实现可能如下所示：

Procedure SetCanvasZoomAndRotation(ACanvas: TCanvas; Zoom: Double;
  Angle: Double; CenterpointX, CenterpointY: Double);
var
  form: tagXFORM;
  rAngle: Double;
begin
  rAngle := DegToRad(Angle);
  SetGraphicsMode(ACanvas.Handle, GM_ADVANCED);
  SetMapMode(ACanvas.Handle, MM_ANISOTROPIC);
  form.eM11 := Zoom * Cos(rAngle);
  form.eM12 := Zoom * Sin(rAngle);
  form.eM21 := Zoom * (-Sin(rAngle));
  form.eM22 := Zoom * Cos(rAngle);
  form.eDx := CenterpointX;
  form.eDy := CenterpointY;
  SetWorldTransform(ACanvas.Handle, form);
end;

Procedure ResetCanvas(ACanvas: TCanvas);
begin
  SetCanvasZoomAndRotation(ACanvas, 1, 0, 0, 0);
end;

您可以在绘画前为所需的画布定义“缩放”，“X Y Offest”和“旋转”。 在您的情况下，您将选择“缩放”，“绘制到画布”以及滚动/减小X和/或Y的值，并再次使用相同的缩放调用该过程并绘制图形。

修改 显示如何使用该过程。这段代码

procedure TForm2.PaintBox1Paint(Sender: TObject);
var
  i, w, h: Integer;
  C: TCanvas;
begin
  C := TPaintBox(Sender).Canvas;
  w := TPaintBox(Sender).Width;
  h := TPaintBox(Sender).Height;
  for i := 0 to 9 do
  begin
    SetCanvasZoomAndRotation(C, 1 + i / 5, i * 36, w div 2, h div 2);
    C.Draw(0, 0, Image1.Picture.Graphic);
    C.Brush.Style := bsClear;
    C.TextOut(50, 0, Format('Hi this is an example %d', [i]));
  end;
end;

用于显示以下结果：

作为对评论的回应，如何将其与轨道栏一起使用，您实现了类似

的内容

procedure TForm2.FormCreate(Sender: TObject);
begin
  DoubleBuffered := true;
end;

procedure TForm2.PaintBox1Paint(Sender: TObject);
var             // a Paintbox aligned alClient
  C:TCanvas;
begin
  TrackBarHorz.Max := Round(Image1.Picture.Graphic.Width * SpinEditZoomInPercent.Value / 100 - TPaintBox(Sender).Width);
  TrackBarVert.Max := Round(Image1.Picture.Graphic.Height * SpinEditZoomInPercent.Value / 100 - TPaintBox(Sender).Height);
  C := TPaintBox(Sender).Canvas;
  SetCanvasZoomAndRotation(c , SpinEditZoomInPercent.Value / 100, 0
                           , - TrackBarHorz.Position
                           , - TrackBarVert.Position);
  C.Draw(0,0,Image1.Picture.Graphic);
end;

procedure TForm2.SpinEditZoomInPercentChange(Sender: TObject);
begin
   PaintBox1.Invalidate;
end;

procedure TForm2.BothTrackbarsEvent(Sender: TObject);
begin
   PaintBox1.Invalidate;
end;