Re: How do I rotate a bitmap fast with high quality?

On Nov 21, 9:32 pm, "[Jongware]" <so...@xxxxxxxxxxx> wrote:
hitxinyu wrote:
the following Demo method is know as this:
// method one is faster,but has a low quality.
// method two has a high quality, but It's too slow for me.
though,I could change double type to float type,
and change float to int using fixed point algorithm.
I want to know a new algorithm, with high quality and faster speed.

void CTestBmpRotateView::RotateAnyAngle(HDC dcSrc,int SrcWidth,int
SrcHeight,double angle,HDC hDC)

[snip heavy example, straight out of starters' manual]

Both methods use Windows functions, either BitBlt or GetPixel/PutPixel.
Using your own buffer is msot likely faster than anything Windows can do.

Method 1: using a BitBlt to copy *a single pixel* from one image to
another? Madness.

Method 2: this samples the pixels at the source image around the
transformed (rotated) point and recalculates the target in RGB. Not bad,
but using Windows' read/write methods, extremely slow. I did this in
plain C, in true color, in real time, a decade ago.

 >though,I could change double type to float type,
 >and change float to int using fixed point algorithm.

About that same time, I learned that everything I knew about converting
floats to fixed point was useless because the floating point
calculations were made vastly faster. Currently, the same goes for
converting doubles to floats -- the "native" format of FPUs is now
double, and converting to /floats/ may take time.

To improve on /this/ algorithm, you should not concentrate on making it
do its dumb stuff faster. Instead, re-write the routine to use
incremental updating of its variables.

[Jongware]

1. Get(Set) pixel;
Method 1: using a BitBlt to copy *a single pixel* from one image
to
another? Madness.
I have said that this just a demo to show bilinear interpolation.and I
also don't know the name of the method one
2.incremental? how to do it in detail?
3.this method may be using in a device with no hardware implement of
the floating point calculations
4.waite later, I will show another implement for bilinear
interpolation.
it will be complex for some reason.
.

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