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How to optimize a software blitter?

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Vanukoff    122
For reasons that I won''t go into, I''m writing a 256 color software blitter. Here is what I have so far: I have a blitter structure that I use to hold blitter stuff:

struct Blitter
    UCHAR* dest_bfr;  // pointer to destination buffer

    int dest_pitch;    // byte width of destination buffer

    int dest_x;
    int dest_y;

    UCHAR* source_bfr;  // pointer to source buffer

    int source_pitch;    // byte width of source buffer

    int source_x;
    int source_y;

    int width;
    int height;
} blitter;

I figured I could do that, to avoid sending 10 parameters to my blitting function. Is this a good idea? Here is the blitter function (it is a straight blitter, no clipping, no transparency):

void BlitNoClip(void)
    int d_off = dest_pitch * dest_y + dest_x; // initial destination buffer offset

    int s_off = source_pitch * source_y + source_x; // initial source buffer offset

    for(int y=0; y<height; y++)
        for(x=0; x<width; x++)
            dest_bfr[d_off+x] = source_bfr[s_off+x];
        d_off += d_pitch;
        s_off += s_pitch;

One optimization I see is to replace the inner loop assignment with a memcpy. What other optimizations can I make? Currently it runs OK, but not nearly as fast as I''d like. Thanks.

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theprogrammer    122
Hello Vanukoff!

I can give you some tips on optimization. So, let''s go:

- Your memcpy idea is a good start. Memcpy on most compilers is quite fast because it uses CPU fast memory instructions like MOVSD ;

- Avoid mul''s. If memory is not an issue, you should use lookup tables;

- There are too fields in your struct. I took it off dest_x, dest_y and dest_pitch. They could change a lot, and you''ll have to access the struct all the time. This is a waste of time. This information can be passed using parameters. Here you need 3 parameters : dest_x, dest_y and dest_surf. I don''t know if you are using DirectDraw or Allegro. However if you got DirectDraw you can pass as paramaters : dest_x,dest_y and dest_surfd (The destination surface''s DDSURFACEDESC2);

- There are two ways to improve blitting, but things will start getting difficult : Assembly language and Direct3D (or OpenGL). The latter is not recommended for dynamic surfaces, like fire;

Good luck!


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