[FFmpeg-soc] [PATCH] Add fade filter to libavfilter

[Brandon Mintern]

On Wed, Mar 31, 2010 at 5:19 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Wed, Mar 31, 2010 at 01:23:29AM -0400, Brandon Mintern wrote:
>> On Wed, Mar 31, 2010 at 12:43 AM, Brandon Mintern <bmintern at gmail.com> wrote:
>> > I am happy to present my first-ever open source code contribution, a
>> > "fade" filter for libavfilter!
>> [snip]
> [...]
>
>> +static void draw_slice(AVFilterLink *link, int y, int h, int slice_dir)
>> +{
>> +    FadeContext *fade = link->dst->priv;
>> +    AVFilterPicRef *in  = link->cur_pic;
>> +    AVFilterPicRef *out = link->dst->outputs[0]->outpic;
>> +    uint8_t *inrow, *outrow;
>> +    int i, j, plane;
>> +
>> +    /* luma plane */
>> +    inrow  = in-> data[0] + y * in-> linesize[0];
>> +    outrow = out->data[0] + y * out->linesize[0];
>> +    for(i = 0; i < h; i ++) {
>> +        for(j = 0; j < link->w; j ++)
>> +            outrow[j] = (uint8_t) ((float) inrow[j] * fade->fade_factor + 0.5);
>
> please avoid floats, it makes regression testing unneccesarily hard
> Its probably ok to use floats/doubles in init, but it feels wrong
> at the pixel level
>
> anyway, real review and approval left to vitor or bobby
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Thanks for the feedback. The line you indicated is actually just an
explicit cast that I can remove if you'd like. However, the
floating-point arithmetic is being used to calculate the new pixel
values and round them to the nearest uint8_t. I can instead stick to
integer arithmetic, but then the numbers will be truncated instead of
rounded. Do you have another suggestion? Is AVRational (I think that's
what it called) something I should be using instead?

Brandon