TPaintBox使用SetWorldTransform旋转图像

问题描述

我正在将图像加载到${myObject.render} 中，然后尝试按照SetWorldTransform中的建议使用this answer旋转图像：

图片可以通过TPaintBox很好地加载。
但是，当我单击测试按钮TPaintBox.Invalidate -> TPaintBox.OnPaint时， 我看到图像闪烁但没有旋转。

BtnRotateWorldTransform

使用

procedure TFrmRotateImage.FormCreate(Sender: TObject);
begin
  FWICImage := TWICImage.Create; 
end;

procedure TFrmRotateImage.BtnLoadPaintBoxClick(Sender: TObject);
begin
   if DlgOpen.Execute then  // PNG or JPG file
   begin
      try
         FWICImage.LoadFromFile(DlgOpen.FileName);
         FBoxLoaded := true;
         PaintBox.Invalidate;
      finally
      end;
   end;
end;

procedure TFrmRotateImage.PaintBoxPaint(Sender: TObject);  // OnPaint handler
begin
   if not FBoxLoaded then Exit;
   PaintBox.Canvas.Draw(0,FWICImage);
end;

procedure TFrmRotateImage.BtnRotateWorldTransformClick(Sender: TObject);  // Test button
var
   lRect: TRect;
begin
   lRect.Top    := PaintBox.Top;
   lRect.Left   := PaintBox.Left;
   lRect.Width  := PaintBox.Width;
   lRect.Height := PaintBox.Height;
   StretchDrawRotated(PaintBox.Canvas,lRect,90,lRect.CenterPoint,FWICImage);
   PaintBox.Invalidate;
end;

我忘记了什么？

解决方法

我写了一个完整的例子。在此示例中，我展示了如何旋转，平移，缩放图像并结合这些转换。

为此，我编写了3个函数来轻松准备旋转，缩放和平移。

在PaintBox1Paint事件处理程序中，我将固定值用于旋转，缩放和平移。当然，在正常的应用程序中，它来自其他地方（例如UI）。转换计算应在PaintBox1Paint过程之外，并在每次参数变化时进行。然后应调用Invalidate，以便使用新的计算出的转换对其进行重新绘制。

procedure TForm4.FormCreate(Sender: TObject);
begin
    FWICImage := TWICImage.Create;
end;

procedure TForm4.FormDestroy(Sender: TObject);
begin
    FreeAndNil(FWICImage);
end;

procedure TForm4.LoadImageButtonClick(Sender: TObject);
begin
    FWICImage.LoadFromFile('C:\Users\fpiette\Pictures\Delphi25 ICS.jpg');
    FBoxLoaded := TRUE;
    PaintBox1.Invalidate;
end;

function XForm_SetRotation(
    AAngle     : Single;
    ACenter    : TPoint) : TXForm;
var
    SinA,CosA: Extended;
begin
    SinCos(AAngle,SinA,CosA);
    Result.eM11 := CosA;
    Result.eM12 := SinA;
    Result.eM21 := -SinA;
    Result.eM22 := CosA;
    Result.eDx := (ACenter.X - (CosA * ACenter.X)) + ((SinA * ACenter.Y));
    Result.eDy := (ACenter.Y - (SinA * ACenter.X)) - ((CosA * ACenter.Y));
end;

function XForm_SetScale(
    const AZoomX : Single;
    const AZoomY : Single;
    const center: TPoint) : TXForm;
begin
    Result.eM11 := AZoomX;
    Result.eM12 := 0.0;
    Result.eM21 := 0.0;
    Result.eM22 := AZoomY;
    Result.eDx  := center.x - AZoomX * center.x;
    Result.eDy  := center.y - AZoomY * center.y;
end;

function XForm_SetTranslate(
    const ADistX : Integer;
    const ADistY : Integer) : TXForm;
begin
    Result.eM11 := 1.0;
    Result.eM12 := 0.0;
    Result.eM21 := 0.0;
    Result.eM22 := 1.0;
    Result.eDx  := ADistX;
    Result.eDy  := ADistY;
end;

procedure TForm4.PaintBox1Paint(Sender: TObject);
var
    XFormScale  : TXForm;
    XFormRot    : TXForm;
    XFormXLat   : TXForm;
    XForm       : TXForm;
    XFormOld    : TXForm;
    GMode       : Integer;
    AZoomFactor : Single;
    AAngle      : Single;
    ADistX      : Integer;
    ADistY      : Integer;
    ACanvas     : TCanvas;
begin
    if not FBoxLoaded then
        Exit;

    AZoomFactor := 0.25;
    AAngle      := 30.0;
    ADistX      := 100;
    ADistY      := 200;
    ACanvas     := PaintBox1.Canvas;

    GMode := SetGraphicsMode(ACanvas.Handle,GM_ADVANCED);
    try
        if GetWorldTransform(ACanvas.Handle,XFormOld) then begin
            try
                XFormRot   := XForm_SetRotation(
                                  AAngle,Point(FWICImage.Width div 2,FWICImage.Height div 2));
                XFormScale := XForm_SetScale(
                                  AZoomFactor,AZoomFactor,Point(0,0));
                XFormXLat  := XForm_SetTranslate(ADistX,ADistY);
                CombineTransform(XForm,XFormRot,XFormScale);
                CombineTransform(XForm,XForm,XFormXLat);
                SetWorldTransform(ACanvas.Handle,XForm);
                ACanvas.Draw(0,FWICImage);
            finally
                SetWorldTransform(ACanvas.Handle,XFormOld);
            end;
        end;
    finally
        SetGraphicsMode(ACanvas.Handle,GMode);
    end;
end;