lavfi/gradfun: support named options.

This breaks usage for out-of-range values.

doc/filters.texi

@@ -2665,19 +2665,21 @@ This filter is designed for playback only.  Do not use it prior to
 lossy compression, because compression tends to lose the dither and
 bring back the bands.
 
-The filter takes two optional parameters, separated by ':':
-@var{strength}:@var{radius}
+The filter accepts a list of options in the form of @var{key}=@var{value} pairs
+separated by ":". A description of the accepted options follows.
 
 @var{strength} is the maximum amount by which the filter will change
 any one pixel. Also the threshold for detecting nearly flat
 regions. Acceptable values range from .51 to 64, default value is
-1.2, out-of-range values will be clipped to the valid range.
+1.2.
 
 @var{radius} is the neighborhood to fit the gradient to. A larger
 radius makes for smoother gradients, but also prevents the filter from
 modifying the pixels near detailed regions. Acceptable values are
-8-32, default value is 16, out-of-range values will be clipped to the
-valid range.
+8-32, default value is 16.
+
+Alternatively, the options can be specified as a flat string:
+@var{strength}[:@var{radius}]
 
 @example
 # default parameters

libavfilter/gradfun.h

@@ -26,6 +26,8 @@
 
 /// Holds instance-specific information for gradfun.
 typedef struct GradFunContext {
+    const AVClass *class;
+    double strength;    ///< user specified strength, used to define thresh
     int thresh;    ///< threshold for gradient algorithm
     int radius;    ///< blur radius
     int chroma_w;  ///< width of the chroma planes

libavfilter/version.h

@@ -30,7 +30,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  3
 #define LIBAVFILTER_VERSION_MINOR  28
-#define LIBAVFILTER_VERSION_MICRO 101
+#define LIBAVFILTER_VERSION_MICRO 102
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vf_gradfun.c

@@ -36,12 +36,24 @@
 #include "libavutil/common.h"
 #include "libavutil/cpu.h"
 #include "libavutil/pixdesc.h"
+#include "libavutil/opt.h"
 #include "avfilter.h"
 #include "formats.h"
 #include "gradfun.h"
 #include "internal.h"
 #include "video.h"
 
+#define OFFSET(x) offsetof(GradFunContext, x)
+#define F AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+
+static const AVOption gradfun_options[] = {
+    { "strength", "set the maximum amount by which the filter will change any one pixel", OFFSET(strength), AV_OPT_TYPE_DOUBLE, {.dbl = 1.2}, 0.51, 64, F },
+    { "radius",   "set the neighborhood to fit the gradient to",                          OFFSET(radius),   AV_OPT_TYPE_INT,    {.i64 =  16},    4, 32, F },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(gradfun);
+
 DECLARE_ALIGNED(16, static const uint16_t, dither)[8][8] = {
     {0x00,0x60,0x18,0x78,0x06,0x66,0x1E,0x7E},
     {0x40,0x20,0x58,0x38,0x46,0x26,0x5E,0x3E},
@@ -121,16 +133,18 @@ static void filter(GradFunContext *ctx, uint8_t *dst, const uint8_t *src, int wi
 
 static av_cold int init(AVFilterContext *ctx, const char *args)
 {
+    int ret;
     GradFunContext *gf = ctx->priv;
-    float thresh = 1.2;
-    int radius = 16;
+    static const char *shorthand[] = { "strength", "radius", NULL };
+
+    gf->class = &gradfun_class;
+    av_opt_set_defaults(gf);
 
-    if (args)
-        sscanf(args, "%f:%d", &thresh, &radius);
+    if ((ret = av_opt_set_from_string(gf, args, shorthand, "=", ":")) < 0)
+        return ret;
 
-    thresh = av_clipf(thresh, 0.51, 64);
-    gf->thresh = (1 << 15) / thresh;
-    gf->radius = av_clip((radius + 1) & ~1, 4, 32);
+    gf->thresh = (1 << 15) / gf->strength;
+    gf->radius = av_clip((gf->radius + 1) & ~1, 4, 32);
 
     gf->blur_line = ff_gradfun_blur_line_c;
     gf->filter_line = ff_gradfun_filter_line_c;
@@ -138,7 +152,7 @@ static av_cold int init(AVFilterContext *ctx, const char *args)
     if (ARCH_X86)
         ff_gradfun_init_x86(gf);
 
-    av_log(ctx, AV_LOG_VERBOSE, "threshold:%.2f radius:%d\n", thresh, gf->radius);
+    av_log(ctx, AV_LOG_VERBOSE, "threshold:%.2f radius:%d\n", gf->strength, gf->radius);
 
     return 0;
 }
@@ -252,4 +266,5 @@ AVFilter avfilter_vf_gradfun = {
 
     .inputs    = avfilter_vf_gradfun_inputs,
     .outputs   = avfilter_vf_gradfun_outputs,
+    .priv_class    = &gradfun_class,
 };