Add getter functions for the interface data symbols

Having these symbols be available as functions rather than data is
occasionally more convenient. Implemented this way rather than a
get-codec-by-id style to avoid creating a link-time dependency
between the encoder and the decoder.

Fixes issue #169

Change-Id: I319f281277033a5e7e3ee3b092b9a87cce2f463d

vp8/exports_dec

@@ -1 +1,2 @@
 data vpx_codec_vp8_dx_algo
+text vpx_codec_vp8_dx

vp8/exports_enc

@@ -1 +1,2 @@
 data vpx_codec_vp8_cx_algo
+text vpx_codec_vp8_cx

vp8/vp8_cx_iface.c

@@ -1079,7 +1079,7 @@ static vpx_codec_enc_cfg_map_t vp8e_usage_cfg_map[] =
 #ifndef VERSION_STRING
 #define VERSION_STRING
 #endif
-vpx_codec_iface_t vpx_codec_vp8_cx_algo =
+CODEC_INTERFACE(vpx_codec_vp8_cx) =
 {
     "WebM Project VP8 Encoder" VERSION_STRING,
     VPX_CODEC_INTERNAL_ABI_VERSION,

vp8/vp8_dx_iface.c

@@ -653,7 +653,7 @@ vpx_codec_ctrl_fn_map_t vp8_ctf_maps[] =
 #ifndef VERSION_STRING
 #define VERSION_STRING
 #endif
-vpx_codec_iface_t vpx_codec_vp8_dx_algo =
+CODEC_INTERFACE(vpx_codec_vp8_dx) =
 {
     "WebM Project VP8 Decoder" VERSION_STRING,
     VPX_CODEC_INTERNAL_ABI_VERSION,

vpx/internal/vpx_codec_internal.h

@@ -389,6 +389,20 @@ struct vpx_codec_priv
 #define RECAST(id, x) id##__convert(x)
 
 
+/* CODEC_INTERFACE convenience macro
+ *
+ * By convention, each codec interface is a struct with extern linkage, where
+ * the symbol is suffixed with _algo. A getter function is also defined to
+ * return a pointer to the struct, since in some cases it's easier to work
+ * with text symbols than data symbols (see issue #169). This function has
+ * the same name as the struct, less the _algo suffix. The CODEC_INTERFACE
+ * macro is provided to define this getter function automatically.
+ */
+#define CODEC_INTERFACE(id)\
+vpx_codec_iface_t* id(void) { return &id##_algo; }\
+vpx_codec_iface_t  id##_algo
+
+
 /* Internal Utility Functions
  *
  * The following functions are indended to be used inside algorithms as

vpx/vp8cx.h

@@ -30,6 +30,7 @@
  * be found in AVI files.
  */
 extern vpx_codec_iface_t  vpx_codec_vp8_cx_algo;
+extern vpx_codec_iface_t* vpx_codec_vp8_cx(void);
 
 
 /*

vpx/vp8dx.h

@@ -30,6 +30,7 @@
  * be found in AVI files and other non-Flash uses.
  */
 extern vpx_codec_iface_t  vpx_codec_vp8_dx_algo;
+extern vpx_codec_iface_t* vpx_codec_vp8_dx(void);
 
 /* Include controls common to both the encoder and decoder */
 #include "vp8.h"