avfilter/vf_histogram: add mirrored waveform mode

Added parameter to mirror the waveform (high values are shown on top in column mode)

Signed-off-by: Marton Balint <cus@passwd.hu>

doc/filters.texi

@@ -4751,6 +4751,12 @@ Default value is @code{10}. Allowed range is [1, 255].
 Set mode for @code{waveform}. Can be either @code{row}, or @code{column}.
 Default is @code{row}.
 
+@item waveform_mirror
+Set mirroring mode for @code{waveform}. @code{0} means unmirrored, @code{1}
+means mirrored. In mirrored mode, higher values will be represented on the left
+side for @code{row} mode and at the top for @code{column} mode. Default is
+@code{0} (unmirrored).
+
 @item display_mode
 Set display mode for @code{waveform} and @code{levels}.
 It accepts the following values:

libavfilter/version.h

@@ -31,7 +31,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  3
 #define LIBAVFILTER_VERSION_MINOR  88
-#define LIBAVFILTER_VERSION_MICRO 100
+#define LIBAVFILTER_VERSION_MICRO 101
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vf_histogram.c

@@ -46,6 +46,7 @@ typedef struct HistogramContext {
     int            scale_height;
     int            step;
     int            waveform_mode;
+    int            waveform_mirror;
     int            display_mode;
     int            levels_mode;
     const AVPixFmtDescriptor *desc;
@@ -66,6 +67,7 @@ static const AVOption histogram_options[] = {
     { "waveform_mode", "set waveform mode", OFFSET(waveform_mode), AV_OPT_TYPE_INT, {.i64=0}, 0, 1, FLAGS, "waveform_mode"},
     { "row",   NULL, 0, AV_OPT_TYPE_CONST, {.i64=0}, 0, 0, FLAGS, "waveform_mode" },
     { "column", NULL, 0, AV_OPT_TYPE_CONST, {.i64=1}, 0, 0, FLAGS, "waveform_mode" },
+    { "waveform_mirror", "set waveform mirroring", OFFSET(waveform_mirror), AV_OPT_TYPE_INT, {.i64=0}, 0, 1, FLAGS, "waveform_mirror"},
     { "display_mode", "set display mode", OFFSET(display_mode), AV_OPT_TYPE_INT, {.i64=1}, 0, 1, FLAGS, "display_mode"},
     { "parade",  NULL, 0, AV_OPT_TYPE_CONST, {.i64=1}, 0, 0, FLAGS, "display_mode" },
     { "overlay", NULL, 0, AV_OPT_TYPE_CONST, {.i64=0}, 0, 0, FLAGS, "display_mode" },
@@ -183,29 +185,38 @@ static void gen_waveform(HistogramContext *h, AVFrame *inpicref, AVFrame *outpic
                          int component, int intensity, int offset, int col_mode)
 {
     const int plane = h->desc->comp[component].plane;
+    const int mirror = h->waveform_mirror;
     const int is_chroma = (component == 1 || component == 2);
     const int shift_w = (is_chroma ? h->desc->log2_chroma_w : 0);
     const int shift_h = (is_chroma ? h->desc->log2_chroma_h : 0);
     const int src_linesize = inpicref->linesize[plane];
     const int dst_linesize = outpicref->linesize[plane];
+    const int dst_signed_linesize = dst_linesize * (mirror == 1 ? -1 : 1);
     uint8_t *src_data = inpicref->data[plane];
     uint8_t *dst_data = outpicref->data[plane] + (col_mode ? (offset >> shift_h) * dst_linesize : offset >> shift_w);
-    uint8_t * const dst_line = dst_data;
+    uint8_t * const dst_bottom_line = dst_data + dst_linesize * ((256 >> shift_h) - 1);
+    uint8_t * const dst_line = (mirror ? dst_bottom_line : dst_data);
     const uint8_t max = 255 - intensity;
     const int src_h = FF_CEIL_RSHIFT(inpicref->height, shift_h);
     const int src_w = FF_CEIL_RSHIFT(inpicref->width, shift_w);
     uint8_t *dst, *p;
     int y;
 
+    if (!col_mode && mirror)
+        dst_data += 256 >> shift_w;
     for (y = 0; y < src_h; y++) {
         const uint8_t *src_data_end = src_data + src_w;
         dst = dst_line;
         for (p = src_data; p < src_data_end; p++) {
             uint8_t *target;
-            if (col_mode)
-                target = dst++ + dst_linesize * (*p >> shift_h);
+            if (col_mode) {
+                target = dst++ + dst_signed_linesize * (*p >> shift_h);
+            } else {
+                if (mirror)
+                    target = dst_data - (*p >> shift_w);
                 else
                     target = dst_data + (*p >> shift_w);
+            }
             if (*target <= max)
                 *target += intensity;
             else