Graphics32:使用鼠标拖动平移，使用鼠标滚轮缩放到鼠标光标

Question

我需要在单击并拖动鼠标时实现平移，并向/远离使用鼠标滚轮的鼠标光标进行缩放/取消缩放。(在Delphi 2010中，图像锚定在窗体的左、右、上、下。)

我刚刚安装了Graphics32，并且看到了它的内置滚动条和.Scale是如何实现这一点的。至少能做到这一点是非常容易的。

问题：

对于这类事情，Graphics32是一个好工具吗？还有没有其他的(也许更简单？)可以让我查一下的工具吗？

有没有人有任何关于如何实现上述内容的指导或示例代码？

谢谢。

Answer 1

Graphics32提供了一个名为TImgView32的组件，该组件可以通过设置Scale属性进行缩放。适当的方法是使用OnMouseWheelUp和-Down事件。将触发这些事件的TabStop设置为True，并将Centered设置为False。但是，以这种方式缩放并不符合您希望将缩放操作放在鼠标光标的中心位置的愿望。因此，围绕这一点重新定位和调整大小是一个更好的解决方案。此外，据我所知，图像总是在组件的左上角对齐，因此平移也必须通过重新定位组件来完成。

uses
  Windows, Classes, Controls, Forms, GR32_Image, GR32_Layers, Jpeg;

type
  TForm1 = class(TForm)
    ImgView: TImgView32;
    procedure FormCreate(Sender: TObject);
    procedure ImgViewMouseWheel(Sender: TObject; Shift: TShiftState;
      WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
    procedure ImgViewMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer; Layer: TCustomLayer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  private
    FDragging: Boolean;
    FFrom: TPoint;
  end;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  ImgView.Bitmap.LoadFromFile('D:\Pictures\Mona_Lisa.jpg');
  ImgView.TabStop := True;
  ImgView.ScrollBars.Visibility := svHidden;
  ImgView.ScaleMode := smResize;
end;

procedure TForm1.ImgViewMouseWheel(Sender: TObject; Shift: TShiftState;
  WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
const
  ZoomFactor: array[Boolean] of Single = (0.9, 1.1);
var
  R: TRect;
begin
  MousePos := ImgView.ScreenToClient(MousePos);
  with ImgView, MousePos do
    if PtInRect(ClientRect, MousePos) then
    begin
      R := BoundsRect;
      R.Left := Left + X - Round(ZoomFactor[WheelDelta > 0] * X);
      R.Top := Top + Y - Round(ZoomFactor[WheelDelta > 0] * Y);
      R.Right := R.Left + Round(ZoomFactor[WheelDelta > 0] * Width);
      R.Bottom := R.Top + Round(ZoomFactor[WheelDelta > 0] * Height);
      BoundsRect := R;
      Handled := True;
    end;
end;

procedure TForm1.ImgViewMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer; Layer: TCustomLayer);
begin
  FDragging := True;
  ImgView.Enabled := False; { Temporarily, to get MouseMove to the parent }
  FFrom := Point(X, Y);
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if FDragging then
    ImgView.SetBounds(X - FFrom.X, Y - FFrom.Y, ImgView.Width, ImgView.Height);
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  FDragging := False;
  ImgView.Enabled := True;
  ImgView.SetFocus;
end;

编辑:使用替代TImage而不是TImgView32：

uses
  Windows, Classes, Controls, Forms, Jpeg, ExtCtrls;

type
  TForm1 = class(TForm)
    Image: TImage;
    procedure FormCreate(Sender: TObject);
    procedure FormMouseWheel(Sender: TObject; Shift: TShiftState;
      WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure ImageDblClick(Sender: TObject);
    procedure ImageMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  private
    FDragging: Boolean;
    FFrom: TPoint;
    FOrgImgBounds: TRect;
  end;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  DoubleBuffered := True;
  Image.Picture.LoadFromFile('D:\Pictures\Mona_Lisa.jpg');
  Image.Stretch := True;
  Image.Height := Round(Image.Width * Image.Picture.Height / Image.Picture.Width);
  FOrgImgBounds := Image.BoundsRect;
end;

procedure TForm1.FormMouseWheel(Sender: TObject; Shift: TShiftState;
  WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
const
  ZoomFactor: array[Boolean] of Single = (0.9, 1.1);
var
  R: TRect;
begin
  MousePos := Image.ScreenToClient(MousePos);
  with Image, MousePos do
    if PtInRect(ClientRect, MousePos) and ((WheelDelta > 0) and
      (Height < Self.ClientHeight) and (Width < Self.ClientWidth)) or
      ((WheelDelta < 0) and (Height > 20) and (Width > 20)) then
    begin
      R := BoundsRect;
      R.Left := Left + X - Round(ZoomFactor[WheelDelta > 0] * X);
      R.Top := Top + Y - Round(ZoomFactor[WheelDelta > 0] * Y);
      R.Right := R.Left + Round(ZoomFactor[WheelDelta > 0] * Width);
      R.Bottom := R.Top + Round(ZoomFactor[WheelDelta > 0] * Height);
      BoundsRect := R;
      Handled := True;
    end;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if FDragging then
    Image.SetBounds(X - FFrom.X, Y - FFrom.Y, Image.Width, Image.Height);
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  Image.Enabled := True;
  FDragging := False;
end;

procedure TForm1.ImageDblClick(Sender: TObject);
begin
  Image.BoundsRect := FOrgImgBounds;
end;

procedure TForm1.ImageMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if not (ssDouble in Shift) then
  begin
    FDragging := True;
    Image.Enabled := False;
    FFrom := Point(X, Y);
    MouseCapture := True;
  end;
end;