[FFmpeg-devel] [PATCH v9 3/6] libavcodec/webp: add support for animated WebP

[Tomas Härdin]

> +    for (int y = 0; y < height; y++) {
> +        const uint8_t *src1 = src1_data[0] + y * src1_linesize[0];
> +        const uint8_t *src2 = src2_data[0] + (y + pos_y) *
> src2_linesize[0] + pos_x * src2_step[0];
> +        uint8_t       *dest = dest_data[0] + (y + pos_y) *
> dest_linesize[0] + pos_x * sizeof(uint32_t);
> +        for (int x = 0; x < width; x++) {
> +            int src1_alpha = src1[0];
> +            int src2_alpha = src2[0];
> +
> +            if (src1_alpha == 255) {
> +                memcpy(dest, src1, sizeof(uint32_t));
> +            } else if (src1_alpha + src2_alpha == 0) {
> +                memset(dest, 0, sizeof(uint32_t));
> +            } else {
> +                int tmp_alpha = src2_alpha - ROUNDED_DIV(src1_alpha
> * src2_alpha, 255);
> +                int blend_alpha = src1_alpha + tmp_alpha;
> +
> +                dest[0] = blend_alpha;
> +                dest[1] = ROUNDED_DIV(src1[1] * src1_alpha + src2[1]
> * tmp_alpha, blend_alpha);
> +                dest[2] = ROUNDED_DIV(src1[2] * src1_alpha + src2[2]
> * tmp_alpha, blend_alpha);
> +                dest[3] = ROUNDED_DIV(src1[3] * src1_alpha + src2[3]
> * tmp_alpha, blend_alpha);
> +            }

Is branching and a bunch of function calls (which I hope get optimized
out) really faster than just always doing the blending?

It mgiht also be worthwhile to check 8 bytes at a time against
UINT64_MAX and 0. That doesn't need to hold up this patch though. Same
with the YUVA version.

> +static int blend_frame_into_canvas(WebPContext *s)
> +{
> +    AVFrame *canvas = s->canvas_frame.f;
> +    AVFrame *frame  = s->frame;
> +    int width, height;
> +    int pos_x, pos_y;
> +
> +    if ((s->anmf_flags & ANMF_BLENDING_METHOD) ==
> ANMF_BLENDING_METHOD_OVERWRITE
> +        || frame->format == AV_PIX_FMT_YUV420P) {
> +        // do not blend, overwrite
> +
> +        if (canvas->format == AV_PIX_FMT_ARGB) {
> +            width  = s->width;
> +            height = s->height;
> +            pos_x  = s->pos_x;
> +            pos_y  = s->pos_y;
> +
> +            for (int y = 0; y < height; y++) {
> +                const uint32_t *src = (uint32_t *) (frame->data[0] +
> y * frame->linesize[0]);
> +                uint32_t *dst = (uint32_t *) (canvas->data[0] + (y +
> pos_y) * canvas->linesize[0]) + pos_x;
> +                memcpy(dst, src, width * sizeof(uint32_t));
> +            }

This could be reduced to a single memcpy() when linesizes are equal.
Same for the other memcpy()s

> +static int dispose_prev_frame_in_canvas(WebPContext *s)
> +{
> +    AVFrame *canvas = s->canvas_frame.f;
> +    int width, height;
> +    int pos_x, pos_y;
> +
> +    if ((s->prev_anmf_flags & ANMF_DISPOSAL_METHOD) ==
> ANMF_DISPOSAL_METHOD_BACKGROUND) {
> +        // dispose to background
> +
> +        if (canvas->format == AV_PIX_FMT_ARGB) {
> +            width  = s->prev_width;
> +            height = s->prev_height;
> +            pos_x  = s->prev_pos_x;
> +            pos_y  = s->prev_pos_y;
> +
> +            for (int y = 0; y < height; y++) {
> +                uint32_t *dst = (uint32_t *) (canvas->data[0] + (y +
> pos_y) * canvas->linesize[0]) + pos_x;
> +                memset(dst, 0, width * sizeof(uint32_t));
> +            }

This can be turned into a single memset(), and similarly below

/Tomas