From acd87d41f29bce3283798c10dccf6b00090b0d2d Mon Sep 17 00:00:00 2001
From: Paul B Mahol <onemda@gmail.com>
Date: Thu, 19 Jan 2023 00:25:36 +0100
Subject: [PATCH] avfilter/vf_exposure: reduce copy operations

---
 libavfilter/vf_exposure.c | 60 +++++++++++++++++++++++++++++++--------
 1 file changed, 48 insertions(+), 12 deletions(-)

diff --git a/libavfilter/vf_exposure.c b/libavfilter/vf_exposure.c
index bbe951967b..ff2f156534 100644
--- a/libavfilter/vf_exposure.c
+++ b/libavfilter/vf_exposure.c
@@ -38,43 +38,80 @@ typedef struct ExposureContext {
                     int jobnr, int nb_jobs);
 } ExposureContext;
 
+typedef struct ThreadData {
+    AVFrame *out, *in;
+} ThreadData;
+
 static int exposure_slice(AVFilterContext *ctx, void *arg, int jobnr, int nb_jobs)
 {
     ExposureContext *s = ctx->priv;
-    AVFrame *frame = arg;
-    const int width = frame->width;
-    const int height = frame->height;
+    ThreadData *td = arg;
+    const int width = td->out->width;
+    const int height = td->out->height;
     const int slice_start = (height * jobnr) / nb_jobs;
     const int slice_end = (height * (jobnr + 1)) / nb_jobs;
     const float black = s->black;
     const float scale = s->scale;
 
     for (int p = 0; p < 3; p++) {
-        const int linesize = frame->linesize[p] / 4;
-        float *ptr = (float *)frame->data[p] + slice_start * linesize;
+        const int slinesize = td->in->linesize[p] / 4;
+        const int dlinesize = td->out->linesize[p] / 4;
+        const float *src = (const float *)td->in->data[p] + slice_start * slinesize;
+        float *ptr = (float *)td->out->data[p] + slice_start * dlinesize;
         for (int y = slice_start; y < slice_end; y++) {
             for (int x = 0; x < width; x++)
-                ptr[x] = (ptr[x] - black) * scale;
+                ptr[x] = (src[x] - black) * scale;
 
-            ptr += linesize;
+            ptr += dlinesize;
+            src += slinesize;
+        }
+    }
+
+    if (td->in->data[3] && td->in->linesize[3] && td->in != td->out) {
+        const int slinesize = td->in->linesize[3] / 4;
+        const int dlinesize = td->out->linesize[3] / 4;
+        const float *src = (const float *)td->in->data[3] + slice_start * slinesize;
+        float *ptr = (float *)td->out->data[3] + slice_start * dlinesize;
+        for (int y = slice_start; y < slice_end; y++) {
+            memcpy(ptr, src, width * sizeof(*ptr));
+            ptr += dlinesize;
+            src += slinesize;
         }
     }
 
     return 0;
 }
 
-static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
+static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 {
     AVFilterContext *ctx = inlink->dst;
+    AVFilterLink *outlink = ctx->outputs[0];
     ExposureContext *s = ctx->priv;
     float diff = fabsf(exp2f(-s->exposure) - s->black);
+    ThreadData td;
+    AVFrame *out;
+
+    if (av_frame_is_writable(in)) {
+        out = in;
+    } else {
+        out = ff_get_video_buffer(outlink, outlink->w, outlink->h);
+        if (!out) {
+            av_frame_free(&in);
+            return AVERROR(ENOMEM);
+        }
+        av_frame_copy_props(out, in);
+    }
 
     diff = diff > 0.f ? diff : 1.f / 1024.f;
     s->scale = 1.f / diff;
-    ff_filter_execute(ctx, s->do_slice, frame, NULL,
-                      FFMIN(frame->height, ff_filter_get_nb_threads(ctx)));
+    td.out = out;
+    td.in = in;
+    ff_filter_execute(ctx, s->do_slice, &td, NULL,
+                      FFMIN(out->height, ff_filter_get_nb_threads(ctx)));
 
-    return ff_filter_frame(ctx->outputs[0], frame);
+    if (out != in)
+        av_frame_free(&in);
+    return ff_filter_frame(outlink, out);
 }
 
 static av_cold int config_input(AVFilterLink *inlink)
@@ -91,7 +128,6 @@ static const AVFilterPad exposure_inputs[] = {
     {
         .name           = "default",
         .type           = AVMEDIA_TYPE_VIDEO,
-        .flags          = AVFILTERPAD_FLAG_NEEDS_WRITABLE,
         .filter_frame   = filter_frame,
         .config_props   = config_input,
     },