When an image is flipped, how can I erase the previous image first?

How can I erase the previous figure Delphi/Windows SDK/API when I flip the image?
Http://www.delphi2007.net/DelphiMultimedia/html/delphi_20061026103637202.html
For example, I want to flip the image, but after turning it over, the original image is still in progress, and the original image is stacked with the new image, Code As follows:


For I: = 0 to image1.width do
Begin
With rect1 do
Begin
Left: = I;
Top: = 0;
Right: = I + 1;
Bottom: = image1.height;
End;
With rect2 do
Begin
Left: = (image1.width)-i-1;
Top: = 0;
Right: = (image1.width)-I;
Bottom: = image1.height;
End;
Image1.canvas. copyrect (rect2, image1.canvas, rect1 );
End;

Shouldn't this problem be too difficult ~~~ Top again

Procedure tform1.bmp _ rotate (srcbmp, destbmp: tbitmap; angle: Extended );
VaR
C1x, c1y, c2x, c2y: integer;
P1x, p1y, P2x, p2y: integer;
Radius, N: integer;
ALPHA: extended;
C0, C1, C2, C3: tcolor;
Begin
If srcbmp. width> srcbmp. Height then
Begin
Destbmp. Width: = srcbmp. width;
Destbmp. Height: = srcbmp. width;
End
Else
Destbmp. Width: = srcbmp. height;
Destbmp. Height: = srcbmp. height;
// Convert the angle to the PI value
Angle: = (angle/180) * PI;
// Calculate the center point. You can modify it.
C1x: = srcbmp. Width Div 2;
C1y: = srcbmp. Height Div 2;
C2x: = destbmp. Width Div 2;
C2y: = destbmp. Height Div 2;
// Step number
If c2x <c2y then
N: = c2y
Else
N: = c2x;
Dec (n, 1 );
// Start Rotation
For P2x: = 0 to n do
Begin
For p2y: = 0 to n do
Begin
If P2x = 0 then
ALPHA: = PI/2
Else
ALPHA: = arctan2 (p2y, P2x );
RADIUS: = round (SQRT (P2x * P2x) + (p2y * p2y )));
P1x: = round (radius * Cos (angle + alpha ));
P1y: = round (radius * sin (angle + alpha ));

C0: = srcbmp. Canvas. pixels [c1x + p1x, c1y + p1y];
C1: = srcbmp. Canvas. pixels [c1x-p1x, c1y-p1y];
C2: = srcbmp. Canvas. pixels [c1x + p1y, c1y-p1x];
C3: = srcbmp. Canvas. pixels [c1x-p1y, c1y + p1x];

Destbmp. Canvas. pixels [c2x + P2x, c2y + p2y]: = C0;
Destbmp. Canvas. pixels [c2x-P2x, c2y-p2y]: = C1;
Destbmp. Canvas. pixels [c2x + p2y, c2y-P2x]: = c2;
Destbmp. Canvas. pixels [c2x-p2y, c2y + P2x]: = C3;
End;
Application. processmessages
End;
End;


Procedure tform1.button1click (Sender: tobject );
VaR
Newbmp: tbitmap;
Bitmap: tbitmap;
Angle: integer;
Begin
Bitmap: = tbitmap. Create;
Newbmp: = tbitmap. Create;
Screen. cursor: = crhourglass;
Newbmp. Assign (image1.picture. Bitmap );

Angle: = strtoint (inputbox ('rotate bitmap ', 'Enter the rotation angular', '90 '));
BMP _rotate (newbmp, bitmap, angle );
Image1.picture. bitmap. Assign (Bitmap );
Image1.left: = (self. Width Div 2)-(bitmap. Width Div 2 );
Image1.top: = (self. Height Div 2)-(bitmap. Height Div 2 );
Screen. cursor: = crdefault;
Newbmp. Free;
Bitmap. Free;
End;