[FFmpeg-devel] [PATCH] memcpy-less expand

[Vitor Sessak]

Michael Tison wrote:
> Here's an attempt at the memcpy-less expand. I implemented a
> get_video_buffer for the input pad that'll hand a correctly sized
> buffer to the previous filter.

Thanks for the patch, but I think there is a little misunderstanding 
about memcpy-less expand. When we refer to it, we are actually talking 
about a O(1) expand. In your code, there is this loop:

> +static void draw_expanded_pic(AVFilterPicRef *pic, ExpContext *exp) {
> +    uint8_t *row;
> +    int i, j, plane, vsub, hsub, max_h, max_w, c;
> +    int xoff, yoff;   //< (x,y)offset
> +   
> +    xoff = exp->x;
> +    yoff = exp->y;    
> +
> +    for(i=0; i<4; i++) 
> +        pic->data[i] = pic->pic->data[i];
> +    for(i=0; i<4; i++)
> +        pic->linesize[i] = pic->pic->linesize[i];
> +
> +    for(plane = 0; plane < 3; plane++) {
> +        c    = (plane == 0) ? 0 : 128;
> +        hsub = (plane == 0) ? 0 : exp->hsub;
> +        vsub = (plane == 0) ? 0 : exp->vsub;
> +        max_h = exp->h0 + exp->dh - 1;
> +        max_w = exp->w0 + exp->dw;
> +
> +        row = pic->data[plane] + (max_h >> vsub)*pic->linesize[plane]; 
> +        for(j = max_h >> vsub; j >= 0; j--) {
> +            for(i = max_w >> hsub; i >= 0; i--) {
> +                if(in_region(i<<hsub, j<<vsub, hsub, vsub, exp)) 
> +                    row[i] = *(pic->data[plane] + i + j*pic->linesize[plane] 
> +                               - (xoff >> hsub) - (yoff >> vsub)*pic->linesize[plane]);
> +                else 
> +                    row[i] = c;
> +            }

Where one could replace the inner loop by a memcpy and two memset if 
they inlined the in_region() function. What we would want is a expand 
filter that would just change the pic->data[] pointers and not touch the 
data inside it, but it would need the data[] buffer to be already 
alloc'ed with the right size someway, that's the tricky part.

-Vitor