static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s, AVFrame *p) { size_t x, y; uint8_t *buffer = av_malloc(s->image_linesize * s->height); if (!buffer) return AVERROR(ENOMEM); if (s->blend_op == APNG_BLEND_OP_OVER && avctx->pix_fmt != AV_PIX_FMT_RGBA && avctx->pix_fmt != AV_PIX_FMT_GRAY8A && avctx->pix_fmt != AV_PIX_FMT_PAL8) { avpriv_request_sample(avctx, "Blending with pixel format %s", av_get_pix_fmt_name(avctx->pix_fmt)); return AVERROR_PATCHWELCOME; } // Do the disposal operation specified by the last frame on the frame if (s->last_dispose_op != APNG_DISPOSE_OP_PREVIOUS) { ff_thread_await_progress(&s->last_picture, INT_MAX, 0); memcpy(buffer, s->last_picture.f->data[0], s->image_linesize * s->height); if (s->last_dispose_op == APNG_DISPOSE_OP_BACKGROUND) for (y = s->last_y_offset; y < s->last_y_offset + s->last_h; ++y) memset(buffer + s->image_linesize * y + s->bpp * s->last_x_offset, 0, s->bpp * s->last_w); memcpy(s->previous_picture.f->data[0], buffer, s->image_linesize * s->height); ff_thread_report_progress(&s->previous_picture, INT_MAX, 0); } else { ff_thread_await_progress(&s->previous_picture, INT_MAX, 0); memcpy(buffer, s->previous_picture.f->data[0], s->image_linesize * s->height); } // Perform blending if (s->blend_op == APNG_BLEND_OP_SOURCE) { for (y = s->y_offset; y < s->y_offset + s->cur_h; ++y) { size_t row_start = s->image_linesize * y + s->bpp * s->x_offset; memcpy(buffer + row_start, p->data[0] + row_start, s->bpp * s->cur_w); } } else { // APNG_BLEND_OP_OVER for (y = s->y_offset; y < s->y_offset + s->cur_h; ++y) { uint8_t *foreground = p->data[0] + s->image_linesize * y + s->bpp * s->x_offset; uint8_t *background = buffer + s->image_linesize * y + s->bpp * s->x_offset; for (x = s->x_offset; x < s->x_offset + s->cur_w; ++x, foreground += s->bpp, background += s->bpp) { size_t b; uint8_t foreground_alpha, background_alpha, output_alpha; uint8_t output[4]; // Since we might be blending alpha onto alpha, we use the following equations: // output_alpha = foreground_alpha + (1 - foreground_alpha) * background_alpha // output = (foreground_alpha * foreground + (1 - foreground_alpha) * background_alpha * background) / output_alpha switch (avctx->pix_fmt) { case AV_PIX_FMT_RGBA: foreground_alpha = foreground[3]; background_alpha = background[3]; break; case AV_PIX_FMT_GRAY8A: foreground_alpha = foreground[1]; background_alpha = background[1]; break; case AV_PIX_FMT_PAL8: foreground_alpha = s->palette[foreground[0]] >> 24; background_alpha = s->palette[background[0]] >> 24; break; } if (foreground_alpha == 0) continue; if (foreground_alpha == 255) { memcpy(background, foreground, s->bpp); continue; } if (avctx->pix_fmt == AV_PIX_FMT_PAL8) { // TODO: Alpha blending with PAL8 will likely need the entire image converted over to RGBA first avpriv_request_sample(avctx, "Alpha blending palette samples"); background[0] = foreground[0]; continue; } output_alpha = foreground_alpha + FAST_DIV255((255 - foreground_alpha) * background_alpha); for (b = 0; b < s->bpp - 1; ++b) { if (output_alpha == 0) { output[b] = 0; } else if (background_alpha == 255) { output[b] = FAST_DIV255(foreground_alpha * foreground[b] + (255 - foreground_alpha) * background[b]); } else { output[b] = (255 * foreground_alpha * foreground[b] + (255 - foreground_alpha) * background_alpha * background[b]) / (255 * output_alpha); } } output[b] = output_alpha; memcpy(background, output, s->bpp); } } } // Copy blended buffer into the frame and free memcpy(p->data[0], buffer, s->image_linesize * s->height); av_free(buffer); return 0; }