configure: allow disabling experimental swscale code

In theory we can also expand this to disable e.g. experimental codecs.

configure

@@ -108,6 +108,7 @@ Configuration options:
   --disable-runtime-cpudetect disable detecting CPU capabilities at runtime (smaller binary)
   --enable-gray            enable full grayscale support (slower color)
   --disable-swscale-alpha  disable alpha channel support in swscale
+  --enable-unstable        enable building optional unstable / experimental code
   --disable-all            disable building components, libraries and programs
   --disable-autodetect     disable automatically detected external libraries [no]
 
@@ -2073,6 +2074,7 @@ FEATURE_LIST="
     small
     static
     swscale_alpha
+    unstable
 "
 
 # this list should be kept in linking order
@@ -4135,7 +4137,7 @@ avutil_suggest="clock_gettime ffnvcodec gcrypt libm libdrm libmfx opencl openssl
 swresample_deps="avutil"
 swresample_suggest="libm libsoxr stdatomic"
 swscale_deps="avutil"
-swscale_suggest="libm stdatomic"
+swscale_suggest="libm stdatomic unstable"
 
 avcodec_extralibs="pthreads_extralibs iconv_extralibs dxva2_extralibs liblcevc_dec_extralibs lcms2_extralibs"
 avfilter_extralibs="pthreads_extralibs"

libswscale/Makefile

@@ -15,11 +15,6 @@ OBJS = alphablend.o                                     \
        graph.o                                          \
        input.o                                          \
        lut3d.o                                          \
-       ops.o                                            \
-       ops_backend.o                                    \
-       ops_chain.o                                      \
-       ops_memcpy.o                                     \
-       ops_optimizer.o                                  \
        options.o                                        \
        output.o                                         \
        rgb2rgb.o                                        \
@@ -31,6 +26,13 @@ OBJS = alphablend.o                                     \
        yuv2rgb.o                                        \
        vscale.o                                         \
 
+OBJS-$(CONFIG_UNSTABLE) +=                              \
+       ops.o                                            \
+       ops_backend.o                                    \
+       ops_chain.o                                      \
+       ops_memcpy.o                                     \
+       ops_optimizer.o                                  \
+
 # Objects duplicated from other libraries for shared builds
 SHLIBOBJS                    += log2_tab.o half2float.o
 

libswscale/format.c

@@ -605,6 +605,8 @@ int sws_is_noop(const AVFrame *dst, const AVFrame *src)
     return 1;
 }
 
+#if CONFIG_UNSTABLE
+
 /* Returns the type suitable for a pixel after fully decoding/unpacking it */
 static SwsPixelType fmt_pixel_type(enum AVPixelFormat fmt)
 {
@@ -1536,3 +1538,5 @@ int ff_sws_encode_colors(SwsContext *ctx, SwsPixelType type,
         .convert.to = fmt_pixel_type(fmt.format),
     });
 }
+
+#endif /* CONFIG_UNSTABLE */

libswscale/graph.c

@@ -463,6 +463,7 @@ static int add_legacy_sws_pass(SwsGraph *graph, SwsFormat src, SwsFormat dst,
  * Format conversion *
  *********************/
 
+#if CONFIG_UNSTABLE
 static int add_convert_pass(SwsGraph *graph, SwsFormat src, SwsFormat dst,
                             SwsPass *input, SwsPass **output)
 {
@@ -536,6 +537,9 @@ fail:
         return add_legacy_sws_pass(graph, src, dst, input, output);
     return ret;
 }
+#else
+#define add_convert_pass add_legacy_sws_pass
+#endif
 
 
 /**************************

libswscale/x86/Makefile

@@ -18,7 +18,7 @@ X86ASM-OBJS                     += x86/input.o                          \
                                    x86/yuv2yuvX.o                       \
 
 ifdef ARCH_X86_64
-X86ASM-OBJS                     += x86/ops_int.o                        \
+X86ASM-OBJS-$(CONFIG_UNSTABLE)  += x86/ops_int.o                        \
                                    x86/ops_float.o                      \
                                    x86/ops.o
 endif