问如何在正确保持纵横比的情况下进行缩放

EN

unit ZImage;

interface

uses
  Windows, Messages, SysUtils,jpeg, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls;

type
  TZImage = class(TGraphicControl)
  private
    FBitmap        : Tbitmap;
    PicRect        : TRect;
    ShowRect       : TRect;
    FShowBorder    : boolean;
    FBorderWidth   : integer;
    FForceRepaint  : boolean;
    FMouse         : (mNone, mDrag, mZoom);
    FProportional  : boolean;
    FDblClkEnable  : boolean;
    FLeft        :integer;
    FRight        :integer;
    FTop             :integer;
    FBottom             :integer;
    startx, starty,
    oldx, oldy     : integer;
    procedure SetShowBorder(s:boolean);
    procedure SetBitmap(b:TBitmap);
    procedure SetBorderWidth(w:integer);
    procedure SetProportional(b:boolean);
  protected
    procedure Paint; override;
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState;
                        X, Y: Integer); override;
    procedure MouseMove(Shift: TShiftState; X, Y: Integer); override;
    procedure MouseUp(Button: TMouseButton; Shift: TShiftState;
              X, Y: Integer); override;
  public
    constructor Create(AOwner:TComponent); override;
    destructor Destroy; override;
    procedure DblClick; override;
  published
  procedure zoom(Endleft,EndRight,EndTop,EndBottom:integer);
    property ValueLeft    : integer read FLeft write FLeft;
    property ValueRight    : Integer read FRight write FRight;
    Property ValueTop         : Integer read FTop write FTop;
    Property ValueBottom         : Integer read FBottom write FBottom;
    property ShowBorder : boolean
                 read FShowBorder
                 write SetShowBorder default true;
    property KeepAspect : boolean
                 read FProportional
                 write SetProportional default true;
    property Bitmap : TBitmap
                 read FBitmap
                 write Setbitmap;
    property BorderWidth : integer
                 read FBorderWidth
                 write SetBorderWidth default 7;
    property ForceRepaint : boolean
                 read FForceRepaint
                 write FForceRepaint default true;
    property DblClkEnable : boolean
                 read FDblClkEnable
                 write FDblClkEnable default False;
    property Align;
    property Width;
    property Height;
    property Top;
    property Left;
    property Visible;
    property Hint;
    property ShowHint;
  end;

procedure Register;

implementation

 //This is the basic create options.
constructor TZImage.Create(AOwner:TComponent);
begin
   inherited;
   FShowBorder:=True;
   FBorderWidth:=7;
   FMouse:=mNone;
   FForceRepaint:=true;    //was true
   FDblClkEnable:=False;
   FProportional:=true;   //was true
   Width:=100; Height:=100;
   FBitmap:=Tbitmap.Create;
   FBitmap.Width:=width;
   FBitmap.height:=Height;
   ControlStyle:=ControlStyle+[csOpaque];
   autosize:= false;
   //Scaled:=false;
end;


//basic destroy frees the FBitmap
destructor TZImage.Destroy;
begin
   FBitmap.Free;
   inherited;
end;

//This was a custom zoom i was using to give the automated zoom effect
procedure TZimage.zoom(Endleft,EndRight,EndTop,EndBottom:integer);
begin

   while ((Endbottom <> picrect.bottom) or (Endtop <> picrect.top)) or ((endleft <> picrect.left) or (endright <> picrect.right)) do
     begin
       if picrect.left > endleft then
            picrect.left := picrect.left -1;
       if picrect.left < endleft  then  //starting
            picrect.left := picrect.left +1;

       if picrect.right > endright then   //starting
            picrect.right := picrect.right -1;
       if picrect.right < endright  then
            picrect.right := picrect.right +1;

       if picrect.top > endtop then
            picrect.top := picrect.top -1;
       if picrect.top < endtop then //starting
            picrect.top := picrect.top +1;

       if picrect.bottom > endbottom then  //starting
            picrect.bottom := picrect.bottom -1;
       if picrect.bottom < endbottom  then
           picrect.bottom := picrect.bottom +1;
       self.refresh;
     end;

end;

//this is the custom paint I know if i put
//Canvas.Draw(0,0,FBitmap);  as the methond it displays
//perfect but the zoom option is gone of course and
//i need the Zoom.
procedure TZImage.Paint;
var buf:TBitmap;
    coef,asps,aspp:Double;
    sz,a : integer;
begin

   buf:=TBitmap.Create;
   buf.Width:=Width;
   buf.Height:=Height;
   if not FShowBorder
     then ShowRect:=ClientRect
     else ShowRect:=Rect(ClientRect.Left,ClientRect.Top,
                         ClientRect.Right-FBorderWidth,
                         ClientRect.Bottom-FBorderWidth);
   ShowRect:=ClientRect;
   with PicRect do begin
    if Right=0 then Right:=FBitmap.Width;
    if Bottom=0 then Bottom:=FBitmap.Height;
   end;
   buf.Canvas.CopyMode:=cmSrcCopy;
   buf.Canvas.CopyRect(ShowRect,FBitmap.Canvas,PicRect);
   Canvas.CopyMode:=cmSrcCopy;
   Canvas.Draw(0,0,buf);
   buf.Free;
end;

procedure TZImage.MouseDown(Button: TMouseButton; Shift: TShiftState;
                            X, Y: Integer);
begin

//   if mbLeft<>Button then Exit;
   if not PtInRect(ShowRect,Point(X,Y)) and
      not PtInRect(Rect(ShowRect.Right,ShowRect.Bottom,
                        Width,Height),Point(X,Y)) then Exit;
   if PtInRect(Rect(ShowRect.Right,ShowRect.Bottom,
                    Width,Height),Point(X,Y)) then begin
      DblClick;
      Exit;
   end;
   //here click is in the picture area only
   startx:=x; oldx:=x;
   starty:=y; oldy:=y;
   if mbRight=Button then begin
      MouseCapture:=True;
      FMouse:=mZoom;
      Canvas.Pen.Mode:=pmNot;
   end else begin
      FMouse:=mDrag;
      Screen.Cursor:=crHandPoint;
   end;
end;



function Min(a,b:integer):integer;
begin
   if a<b then Result:=a else Result:=b;
end;
function Max(a,b:integer):integer;
begin
   if a<b then Result:=b else Result:=a;
end;



procedure TZImage.MouseMove(Shift: TShiftState; X, Y: Integer);
var d,s:integer;
    coef:Double;
begin
    if FMouse=mNone then Exit;
    if FMouse=mZoom then begin
       Canvas.DrawFocusRect(Rect(Min(startx,oldx),Min(starty,oldy),Max(startx,oldx),Max(starty,oldy)));
       oldx:=x; oldy:=y;
       Canvas.DrawFocusRect(Rect(Min(startx,oldx),Min(starty,oldy),Max(startx,oldx),Max(starty,oldy)));
    end;
    if FMouse=mDrag then begin
//horizontal movement
       coef:=(PicRect.Right-PicRect.Left)/(ShowRect.Right-ShowRect.Left);
       d:=Round(coef*(x-oldx));
       s:=PicRect.Right-PicRect.Left;
       if d>0 then begin
          if PicRect.Left>=d then begin
            PicRect.Left:=PicRect.Left-d;
            PicRect.Right:=PicRect.Right-d;
          end else begin
            PicRect.Left:=0;
            PicRect.Right:=PicRect.Left+s;
          end;
       end;
       if d<0 then begin
          if PicRect.Right<FBitmap.Width+d then begin
            PicRect.Left:=PicRect.Left-d;
            PicRect.Right:=PicRect.Right-d;
          end else begin
            PicRect.Right:=FBitmap.Width;
            PicRect.Left:=PicRect.Right-s;
          end;
       end;

//vertical movement
       coef:=(PicRect.Bottom-PicRect.Top)/(ShowRect.Bottom-ShowRect.Top);
       d:=Round(coef*(y-oldy));
       s:=PicRect.Bottom-PicRect.Top;
       if d>0 then begin
          if PicRect.Top>=d then begin
            PicRect.Top:=PicRect.Top-d;
            PicRect.Bottom:=PicRect.Bottom-d;
          end else begin
            PicRect.Top:=0;
            PicRect.Bottom:=PicRect.Top+s;
          end;
       end;

{There was a bug in the fragment below. Thanks to all, who reported this bug to me}
      if d<0 then begin
          if PicRect.Bottom<FBitmap.Height+d then begin
            PicRect.Top:=PicRect.Top-d;
            PicRect.Bottom:=PicRect.Bottom-d;
          end else begin
            PicRect.Bottom:=FBitmap.Height;
            PicRect.Top:=PicRect.Bottom-s;
          end;
       end;


       oldx:=x; oldy:=y;
       if FForceRepaint then Repaint
                        else Invalidate;
    end;
end;



procedure TZImage.MouseUp(Button: TMouseButton; Shift: TShiftState;
                          X, Y: Integer);
var coef:Double;
    t:integer;
    left,right,top,bottom : integer;
begin

   if FMouse=mNone then Exit;
   if x>ShowRect.Right then x:=ShowRect.Right;
   if y>ShowRect.Bottom then y:=ShowRect.Bottom;
   if FMouse=mZoom then begin  //calculate new PicRect
     t:=startx;
     startx:=Min(startx,x);
     x:=Max(t,x);
     t:=starty;
     starty:=Min(starty,y);
     y:=Max(t,y);
     FMouse:=mNone;
     MouseCapture:=False;
//enable the following if you want to zoom-out by dragging in the opposite direction}
{     if Startx>x then begin
        DblClick;
        Exit;
     end;}
     if Abs(x-startx)<5 then Exit;
     //showmessage('picrect Left='+inttostr(picrect.Left)+' right='+inttostr(picrect.Right)+' top='+inttostr(picrect.Top)+' bottom='+inttostr(picrect.Bottom));
     //startx and start y is teh starting x/y of the selected area
     //x and y is the ending x/y of the selected area
     if (x - startx < y - starty) then
     begin
       while (x - startx < y - starty) do
       begin
          x := x + 100;
          startx := startx - 100;
       end;
     end

     else if (x - startx > y - starty) then
     begin
        while (x - startx > y - starty) do
        begin
            y := y + 100;
            starty := starty - 100;
        end;
     end;

//picrect is the size of whole area
//PicRect.top and left are 0,0
//IFs were added in v.1.2 to avoid zero-divide
     if (PicRect.Right=PicRect.Left)
     then
        coef := 100000
     else
        coef:=ShowRect.Right/(PicRect.Right-PicRect.Left);    //if new screen coef= 1
     left:=Round(PicRect.Left+startx/coef);
     Right:=Left+Round((x-startx)/coef);

     if (PicRect.Bottom=PicRect.Top)
     then
        coef := 100000
     else
        coef:=ShowRect.Bottom/(PicRect.Bottom-PicRect.Top);
     Top:=Round(PicRect.Top+starty/coef);
     Bottom:=Top+Round((y-starty)/coef);
     //showmessage(inttostr(left)+' '+inttostr(Right)+' '+inttostr(top)+' '+inttostr(bottom));

     zoom(left,right,top,bottom);
     ValueLeft := left;
     ValueRight := Right;
     ValueTop := top;
     ValueBottom := bottom;
     end;
   if FMouse=mDrag then begin
     FMouse:=mNone;
     Canvas.Pen.Mode:=pmCopy;
     Screen.Cursor:=crDefault;
   end;

   Invalidate;
end;

procedure TZImage.DblClick;
begin
   zoom(0,FBitMap.Width,0,FBitMap.Height);
   ValueLeft := 0;
   ValueRight := FBitMap.Width;
   ValueTop := 0;
   ValueBottom := FBitMap.Height;
   //PicRect:=Rect(0,0,FBitmap.Width,FBitmap.Height);
   Invalidate;
end;

procedure TZImage.SetBitmap(b:TBitmap);
begin
   FBitmap.Assign(b);
   PicRect:=Rect(0,0,b.Width, b.Height);
   Invalidate;
end;

procedure TZImage.SetBorderWidth(w:integer);
begin
   FBorderWidth:=w;
   Invalidate;
end;

procedure TZImage.SetShowBorder(s:boolean);
begin
   FShowBorder:=s;
   Invalidate;
end;

procedure TZImage.SetProportional(b:boolean);
begin
   FProportional:=b;
   Invalidate;
end;

procedure Register;
begin
  RegisterComponents('Custom', [TZImage]);
end;

end.