Image shaking when StretchDIBits partially.

Question

I am using C++ GDI, StretchDIBits to draw images on DC.

Because the original Image is large, and high quality is needed. I use HAFTONE mode, to draw whole image on DC(zoom the image) seems time comsuming.

So I decide to draw partially using StretchDIBits. But there is a serious problem about StretchDIBits.

I can only draw rect in integers to a region in integers(the width and height ,and top left point of x, y are all integers)

 ::SetStretchBltMode(hdc, HALFTONE);
 ::StretchDIBits(hdc,
  realDrawRect.left, 
  realDrawRect.top, 
  realDrawRect.right - realDrawRect.left, 
  realDrawRect.bottom - realDrawRect.top,
  left, 
  top, 
  width, 
  height,
  pImageDIB,
  pImageHead, 
  DIB_RGB_COLORS, SRCCOPY);

if, the Image is 21 * 21 . I now is drawing (5, 5, 7, 7) to DC, at (20, 20, 60,60), the next time I wann to draw at (21, 20, 61, 60). there is not corresponding location at original image. So I can only draw an approximation rect to the DC. Now the problem happening, the image is shaking!!

I am annoyed about that problem. How can I avoid shaking?

Answer 1

If the shaking comes from rounding the integer try rounding it down to nearest integer. See this.

Otherwise I would recommend that you switch to GDI+ which is much easier to work with. With GDI+ you can draw a bitmap with floating point precision. See documentation Graphics::DrawImage.

I've switched from GDI to GDI+ in a couple of MFC Active-X projects and it's not hard at all.