Re: [FFmpeg-devel] [PATCH] lsws/swscale.h: introduce sws_get_gaussian_vec

[Stefano Sabatini <stefasab@gmail.com>]

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On date Thursday 2023-08-31 18:51:52 +0200, Andreas Rheinhardt wrote:
> Stefano Sabatini:
> > +int sws_get_gaussian_vec(SwsVector **vecp,
> > +                         AVClass *log_ctx,
> > +                         double standard_deviation, double quality);
> >  
> 
> Seriously? A pointer to an AVClass as log_ctx? It is actually AVClass**
> (the logcontext must have a pointer to an AVClass as its first member),
> but we always use NULL.

Sorry, sloppy editing on my side.

> Apart from that: I am not really convinced that the improvement is worth
> the hassle.

This is not a high-profile function (probably it's never used outside
lavfi) and provides an opportunity to move the API to the correct
direction.

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From 69c33f62e15de3d199d54187d38c0856418f0981 Mon Sep 17 00:00:00 2001
From: Stefano Sabatini <stefasab@gmail.com>
Date: Sat, 26 Aug 2023 14:20:35 +0200
Subject: [PATCH 1/2] lsws/swscale.h: introduce sws_get_gaussian_vec

Use in place of sws_getGaussianVec.

The new function enable better error handling, and provide better naming
for the variance variable, now named standard_deviation to reflect the
meaning of the parameter.
---
 doc/APIchanges             |  3 +++
 libswscale/swscale.h       | 27 +++++++++++++++++++++++-
 libswscale/utils.c         | 42 ++++++++++++++++++++++++++++++--------
 libswscale/version.h       |  2 +-
 libswscale/version_major.h |  4 ++++
 5 files changed, 67 insertions(+), 11 deletions(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index ad1efe708d..bad2d61027 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2023-02-09
 
 API changes, most recent first:
 
+2023-08-26 - xxxxxxxxxx - lsws 7.4.100 - swscale.h
+  Introduce sws_get_gaussian_vec, use in place of sws_getGaussianVec.
+
 2023-08-18 - xxxxxxxxxx - lavu 58.17.100 - channel_layout.h
   All AV_CHANNEL_LAYOUT_* macros are now compatible with C++ 17 and older.
 
diff --git a/libswscale/swscale.h b/libswscale/swscale.h
index 9d4612aaf3..55f2fc4a48 100644
--- a/libswscale/swscale.h
+++ b/libswscale/swscale.h
@@ -355,11 +355,36 @@ int sws_getColorspaceDetails(struct SwsContext *c, int **inv_table,
  */
 SwsVector *sws_allocVec(int length);
 
+#if FF_API_SWS_GET_GAUSSIAN_VEC
 /**
- * Return a normalized Gaussian curve used to filter stuff
+ * Return a normalized Gaussian curve used to filter stuff.
+ *
  * quality = 3 is high quality, lower is lower quality.
+ * @deprecated use sws_get_gaussian_vector()
  */
+attribute_deprecated
 SwsVector *sws_getGaussianVec(double variance, double quality);
+#endif
+
+/**
+ * Compute and return a normalized Gaussian vector.
+ *
+ * @param vecp: pointer where the computed vector is put in case of
+ *        success
+ * @param standard_deviation the standard deviation used to generate
+ *        the Gaussian vector, must be a non-negative value
+ * @param quality the quality of the generated Gaussian vector, must
+ *        be a non-negative value. It affects the lenght of the generated
+ *        vector. A value equal to 3 corresponds to high quality.
+ * @param log_ctx a pointer to an arbitrary struct of which the first
+ *        field is a pointer to an AVClass struct (used for av_log)
+ *        used for logging, can be NULL
+ *
+ * @return a negative error code on error, non negative otherwise
+ */
+int sws_get_gaussian_vec(SwsVector **vecp,
+                         double standard_deviation, double quality,
+                         void *log_ctx);
 
 /**
  * Scale all the coefficients of a by the scalar value.
diff --git a/libswscale/utils.c b/libswscale/utils.c
index 8e74c6603e..fd9b2d33d0 100644
--- a/libswscale/utils.c
+++ b/libswscale/utils.c
@@ -2139,31 +2139,55 @@ SwsVector *sws_allocVec(int length)
     return vec;
 }
 
-SwsVector *sws_getGaussianVec(double variance, double quality)
+int sws_get_gaussian_vec(SwsVector **vecp,
+                         double standard_deviation, double quality,
+                         void *log_ctx)
 {
-    const int length = (int)(variance * quality + 0.5) | 1;
+    const int length = (int)(standard_deviation * quality + 0.5) | 1;
     int i;
     double middle  = (length - 1) * 0.5;
     SwsVector *vec;
+    const double variance = standard_deviation * standard_deviation;
 
-    if(variance < 0 || quality < 0)
-        return NULL;
+    if (standard_deviation < 0 || quality < 0) {
+        av_log(log_ctx, AV_LOG_ERROR,
+               "Invalid negative standard deviation %f or quality %f provided as input to the sws_get_gaussian_vec function\n",
+               standard_deviation, quality);
+        return AVERROR(EINVAL);
+    }
 
     vec = sws_allocVec(length);
-
-    if (!vec)
-        return NULL;
+    if (!vec) {
+        av_log(log_ctx, AV_LOG_ERROR,
+               "Could not allocate vector for the sws_get_gaussian_vec function\n");
+        return AVERROR(ENOMEM);
+    }
 
     for (i = 0; i < length; i++) {
         double dist = i - middle;
-        vec->coeff[i] = exp(-dist * dist / (2 * variance * variance)) /
-                        sqrt(2 * variance * M_PI);
+        vec->coeff[i] = exp(-dist * dist / (2 * variance)) /
+                        sqrt(2 * standard_deviation * M_PI);
     }
 
     sws_normalizeVec(vec, 1.0);
+    *vecp = vec;
 
+    return 0;
+}
+
+#if FF_API_SWS_GET_GAUSSIAN_VEC
+SwsVector *sws_getGaussianVec(double variance, double quality)
+{
+    SwsVector *vec;
+    int ret;
+
+    ret = sws_get_gaussian_vec(&vec, variance, quality, NULL);
+    if (ret < 0) {
+        return NULL;
+    }
     return vec;
 }
+#endif // FF_API_SWS_GET_GAUSSIAN_VEC
 
 /**
  * Allocate and return a vector with length coefficients, all
diff --git a/libswscale/version.h b/libswscale/version.h
index 51eb013a29..12412bd538 100644
--- a/libswscale/version.h
+++ b/libswscale/version.h
@@ -28,7 +28,7 @@
 
 #include "version_major.h"
 
-#define LIBSWSCALE_VERSION_MINOR   3
+#define LIBSWSCALE_VERSION_MINOR   4
 #define LIBSWSCALE_VERSION_MICRO 100
 
 #define LIBSWSCALE_VERSION_INT  AV_VERSION_INT(LIBSWSCALE_VERSION_MAJOR, \
diff --git a/libswscale/version_major.h b/libswscale/version_major.h
index 88577a2b42..aa0baef7c6 100644
--- a/libswscale/version_major.h
+++ b/libswscale/version_major.h
@@ -32,4 +32,8 @@
  * the public API and may change, break or disappear at any time.
  */
 
+#ifndef FF_API_SWS_GET_GAUSSIAN_VEC
+#define FF_API_SWS_GET_GAUSSIAN_VEC       (LIBSWSCALE_VERSION_MAJOR < 8)
+#endif
+
 #endif /* SWSCALE_VERSION_MAJOR_H */
-- 
2.34.1


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