api! Remove the stub functions png_set_filter_heuristics, etc.

The old experiment with delta-filtering heuristics did not work out as expected. Eventually, the functions `png_set_filter_heuristics` and `png_set_filter_heuristics_fixed` became no-ops. We are removing them from libpng-1.8. Signed-off-by: Cosmin Truta <[email protected]>
pnggroup · Sep 25, 2024 · d596351 · d596351
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diff --git a/manuals/libpng.3 b/manuals/libpng.3
@@ -329,10 +329,6 @@ libpng \- Portable Network Graphics (PNG) Reference Library 1.6.44
 
 \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
 
-\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
-
-\fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
-
 \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
 
 \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP

diff --git a/png.h b/png.h
@@ -1474,22 +1474,6 @@ PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
 #define PNG_FILTER_VALUE_LAST  5
 
 #ifdef PNG_WRITE_SUPPORTED
-#ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED /* DEPRECATED */
-PNG_FP_EXPORT(68, void, png_set_filter_heuristics, (png_structrp png_ptr,
-    int heuristic_method, int num_weights, png_const_doublep filter_weights,
-    png_const_doublep filter_costs))
-PNG_FIXED_EXPORT(209, void, png_set_filter_heuristics_fixed,
-    (png_structrp png_ptr, int heuristic_method, int num_weights,
-    png_const_fixed_point_p filter_weights,
-    png_const_fixed_point_p filter_costs))
-#endif /* WRITE_WEIGHTED_FILTER */
-
-/* The following are no longer used and will be removed from libpng-1.7: */
-#define PNG_FILTER_HEURISTIC_DEFAULT    0  /* Currently "UNWEIGHTED" */
-#define PNG_FILTER_HEURISTIC_UNWEIGHTED 1  /* Used by libpng < 0.95 */
-#define PNG_FILTER_HEURISTIC_WEIGHTED   2  /* Experimental feature */
-#define PNG_FILTER_HEURISTIC_LAST       3  /* Not a valid value */
-
 /* Set the library compression level.  Currently, valid values range from
  * 0 - 9, corresponding directly to the zlib compression levels 0 - 9
  * (0 - no compression, 9 - "maximal" compression).  Note that tests have
@@ -1537,6 +1521,14 @@ PNG_EXPORT(225, void, png_set_text_compression_window_bits,
 PNG_EXPORT(226, void, png_set_text_compression_method, (png_structrp png_ptr,
     int method));
 #endif /* WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
+
+PNG_REMOVED(68, void, png_set_filter_heuristics, (png_structrp png_ptr,
+    int heuristic_method, int num_weights, png_const_doublep filter_weights,
+    png_const_doublep filter_costs),PNG_DEPRECATED)
+PNG_REMOVED(209, void, png_set_filter_heuristics_fixed,
+    (png_structrp png_ptr, int heuristic_method, int num_weights,
+    png_const_fixed_point_p filter_weights,
+    png_const_fixed_point_p filter_costs),PNG_DEPRECATED)
 #endif /* WRITE */
 
 /* These next functions are called for input/output, memory, and error

diff --git a/pngtest.c b/pngtest.c
@@ -1696,12 +1696,12 @@ test_one_file(const char *inname, const char *outname)
             {
                fprintf(STDERR,
                    "   Was %s written with the same maximum IDAT"
-                   " chunk size (%d bytes),",
+                   " chunk size (%d bytes),\n",
                    inname, PNG_ZBUF_SIZE);
                fprintf(STDERR,
-                   "\n   filtering heuristic (libpng default), compression");
+                   "   compression level (zlib default),\n");
                fprintf(STDERR,
-                   " level (zlib default),\n   and zlib version (%s)?\n\n",
+                   "   and zlib version (%s)?\n\n",
                    ZLIB_VERSION);
                wrote_question = 1;
             }
@@ -1728,12 +1728,12 @@ test_one_file(const char *inname, const char *outname)
             {
                fprintf(STDERR,
                    "   Was %s written with the same maximum"
-                   " IDAT chunk size (%d bytes),",
+                   " IDAT chunk size (%d bytes),\n",
                     inname, PNG_ZBUF_SIZE);
                fprintf(STDERR,
-                   "\n   filtering heuristic (libpng default), compression");
+                   "   compression level (zlib default),\n");
                fprintf(STDERR,
-                   " level (zlib default),\n   and zlib version (%s)?\n\n",
+                   "   and zlib version (%s)?\n\n",
                  ZLIB_VERSION);
                wrote_question = 1;
             }

diff --git a/pngwrite.c b/pngwrite.c
@@ -1137,37 +1137,6 @@ png_set_filter(png_structrp png_ptr, int method, int filters)
       png_error(png_ptr, "Unknown custom filter method");
 }
 
-#ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED /* DEPRECATED */
-/* Provide floating and fixed point APIs */
-#ifdef PNG_FLOATING_POINT_SUPPORTED
-void PNGAPI
-png_set_filter_heuristics(png_structrp png_ptr, int heuristic_method,
-    int num_weights, png_const_doublep filter_weights,
-    png_const_doublep filter_costs)
-{
-   PNG_UNUSED(png_ptr)
-   PNG_UNUSED(heuristic_method)
-   PNG_UNUSED(num_weights)
-   PNG_UNUSED(filter_weights)
-   PNG_UNUSED(filter_costs)
-}
-#endif /* FLOATING_POINT */
-
-#ifdef PNG_FIXED_POINT_SUPPORTED
-void PNGAPI
-png_set_filter_heuristics_fixed(png_structrp png_ptr, int heuristic_method,
-    int num_weights, png_const_fixed_point_p filter_weights,
-    png_const_fixed_point_p filter_costs)
-{
-   PNG_UNUSED(png_ptr)
-   PNG_UNUSED(heuristic_method)
-   PNG_UNUSED(num_weights)
-   PNG_UNUSED(filter_weights)
-   PNG_UNUSED(filter_costs)
-}
-#endif /* FIXED_POINT */
-#endif /* WRITE_WEIGHTED_FILTER */
-
 #ifdef PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED
 void PNGAPI
 png_set_compression_level(png_structrp png_ptr, int level)

diff --git a/pngwutil.c b/pngwutil.c
@@ -2573,11 +2573,10 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
     * from zero, using anything >= 128 as negative numbers.  This is known
     * as the "minimum sum of absolute differences" heuristic.  Other
     * heuristics are the "weighted minimum sum of absolute differences"
-    * (experimental and can in theory improve compression), and the "zlib
-    * predictive" method (not implemented yet), which does test compressions
-    * of lines using different filter methods, and then chooses the
-    * (series of) filter(s) that give minimum compressed data size (VERY
-    * computationally expensive).
+    * method (experimented, then abandoned), and the "zlib predictive" method
+    * (not implemented yet), which does test compression of lines using
+    * different filter methods, and then chooses the (series of) filter(s)
+    * that give minimum compressed data size (VERY computationally expensive).
     *
     * GRR 980525:  consider also
     *

diff --git a/scripts/pnglibconf.dfa b/scripts/pnglibconf.dfa
@@ -648,8 +648,6 @@ option WRITE_USER_TRANSFORM requires WRITE_TRANSFORMS
 option WRITE_INTERLACING requires WRITE
 
 # Deprecated, will be removed.
-option WRITE_WEIGHTED_FILTER requires WRITE
-
 option WRITE_FLUSH requires WRITE
 
 # Note: these can be turned off explicitly if not required by the

diff --git a/scripts/pnglibconf.h.prebuilt b/scripts/pnglibconf.h.prebuilt
@@ -155,7 +155,6 @@
 #define PNG_WRITE_TRANSFORMS_SUPPORTED
 #define PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
 #define PNG_WRITE_USER_TRANSFORM_SUPPORTED
-#define PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
 #define PNG_WRITE_bKGD_SUPPORTED
 #define PNG_WRITE_cHRM_SUPPORTED
 #define PNG_WRITE_eXIf_SUPPORTED

diff --git a/scripts/symbols.def b/scripts/symbols.def
@@ -71,7 +71,6 @@ EXPORTS
  png_destroy_write_struct @65
  png_set_crc_action @66
  png_set_filter @67
- png_set_filter_heuristics @68
  png_set_compression_level @69
  png_set_compression_mem_level @70
  png_set_compression_strategy @71
@@ -211,7 +210,6 @@ EXPORTS
  png_save_int_32 @206
  png_save_uint_16 @207
  png_set_gamma_fixed @208
- png_set_filter_heuristics_fixed @209
  png_get_pixel_aspect_ratio_fixed @210
  png_get_x_offset_inches_fixed @211
  png_get_y_offset_inches_fixed @212