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Possible Optimization

Started by aprentice Dec 31, 2004 at 8:42 PM 6 replies 600+ views

Original Post

Dec 31, 2004 at 8:42 PM

I have done some timing to see where I lose speed in my current pixel drawing routine and I have tracked it down to the following line where the function memcpy is used. int offset=((ly)+(x*main.pixelwidth)); memcpy(szSurface+offset,&bgpal[pixel],main.pixelwidth); bgpal is an array that holds the palette for the specified pixel. I was wondering if anyone has any optimization ideas. I'm using direct draw btw. Thanks in advance

Basiror

Dec 31, 2004 at 8:53 PM

why do you do it per pixel?

aprentice

Dec 31, 2004 at 9:06 PM

Quote:
Original post by Basiror
why do you do it per pixel?

I interpret data, sort of like bitmaps do, but not exactly the same.

JohnBolton

Dec 31, 2004 at 10:38 PM

Rather than using memcpy, write 4 different blitting functions -- one for each pixel size, and use normal assignment to set the pixel's value. There might be some clever optimizations that you can use, but try this first.

Your 32-bit per pixel blitting code might look something like this:

    unsigned __int32 bgpal[256];    ...    unsigned __int8 * srcrow = srcSurface + src_y * srcpitch + src_x;    unsigned __int8 * dstrow = dstSurface + dst_y * dstpitch + dst_x * 4;         for ( int y = 0; y < h; ++y )    {        unsigned __int8  * src = srcrow;        unsigned __int32 * dst = dstrow;            for ( int x = 0; x <= w; ++x )        {            dst[x] = bgpal[ src[x] ];        }        srcrow += srcpitch;        dstrow += dstpitch;    }

trevaaar

Dec 31, 2004 at 10:40 PM

try to just assign the values directly instead of using memcpy if you are going to do it pixel-by-pixel

aprentice

Jan 2, 2005 at 1:50 AM

I have tried the following code:

init:
unsigned int *lszSurface = ddsd.lpSurface;

draw_func:
int offset=((ly)+(x*main.pixelwidth));
lszSurface[offset] = bgpal[pixel];

The image isnt exactly comming out right, there space in between every pixel (approx. 4?), it may be 3am in the morning, but I don't see anything wrong...

Muhammad Haggag

Jan 2, 2005 at 5:01 AM

Quote:
Original post by aprentice
int offset=((ly)+(x*main.pixelwidth));
lszSurface[offset] = bgpal[pixel];

Assuming main.pixelwidth == pitch, it should be:
offset = ly * main.pixelwidth + x

aprentice

Jan 2, 2005 at 10:54 AM

thanks for your help guys, I've got it working now :)

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