Use iplRotate the picture what I get is losing the part of left and right .why?

Question

the code is create CreateImageHeader for two :imageSo and imageDe, then value imagedata by scanline , then rotate by judge angle, then value scanline by imagedata,

I show the main code like what I said as behind,hope someone could give me the suggestion or thinking.

create:

imageSo = CreateImageHeader(bmp->PixelFormat, bmp->Width,bmp->Height);  
imageDe = CreateImageHeader(bmp->PixelFormat, bmp->Width,bmp->Height);  

shift:

bit1=(BYTE*) bmp->ScanLine[hSrc-1];  
bit2=imageSo->imageData;  
for(int i=0;i < hSrc;i++)    
{  
    memcpy(bit2,bit1,cpy);  
    bit1+=wBmp;  
    bit2+=wIpl;  
}  

rotate:

if(param.Angle){  

double xshift=0;  

double yshift=0;  

iiplGetRotateShift(bmp->Width/2,bmp->Height/2,BmpProperty.Angle,&xshift,&yshift);    

iiplRotate(imageSo,imageDe,BmpProperty.Angle,xshift,yshift,IPL_INTER_CUBIC|IPL_SMOOTH_EDGE);  
}  

shift2:

bit1=(BYTE*) bmp->ScanLine[hSrc-1];  
bit2=imageSo->imageData;  
for(int i=0;i < hSrc;i++)   
{  
    memcpy(bit1,bit2,cpy);  
    bit1+=wBmp;  
    bit2+=wIpl;  
}   

Answer 1

I know the reason now , because after rotated, the canvas was also rotating,so I set the canvas to be a square which was rectangle before.also understand the picture in canvas's position would also help.

here is the website which is introduce the details of canvas rotate. enter link description here