Add comments to webpanim shim

* Also for d >= 8, write output in format specifed by the extension name.

prog/scaletest1.c

@@ -30,6 +30,10 @@
  *      scaletest1 filein scalex scaley fileout
  *    where
  *      scalex, scaley are floating point input
+ *
+ *  For d < 8 bpp, writes output in png
+ *  For d >= 8 bpp, uses output file extension to determine output format.
+ *
  */
 
 #ifdef HAVE_CONFIG_H
@@ -42,7 +46,7 @@ int main(int    argc,
          char **argv)
 {
 char      *filein, *fileout;
-l_int32    d;
+l_int32    d, fmt;
 l_float32  scalex, scaley;
 PIX       *pixs, *pixd;
 
@@ -75,14 +79,12 @@ PIX       *pixs, *pixd;
 
     d = pixGetDepth(pixd);
 
-#if 1
-    if (d <= 8)
+    if (d < 8) {
         pixWrite(fileout, pixd, IFF_PNG);
-    else
-        pixWrite(fileout, pixd, IFF_JFIF_JPEG);
-#else
-    pixWrite(fileout, pixd, IFF_PNG);
-#endif
+    } else {
+        fmt = getImpliedFileFormat(fileout);
+        pixWrite(fileout, pixd, fmt);
+    }
 
     pixDestroy(&pixs);
     pixDestroy(&pixd);

src/webpanimio.c

@@ -32,6 +32,19 @@
  *          l_int32          pixaWriteWebPAnim()
  *          l_int32          pixaWriteStreamWebPAnim()
  *          l_int32          pixaWriteMemWebPAnim()
+ *
+ * This shim was written in 2013, shortly after Google introduced animated webp.
+ * However, even though animated webp is better than gifanim by every
+ * technical measure (e.g., flexibility, compression), animated webp
+ * is still not well supported, even with Google apps like gmail!
+ *
+ * To convert from gifanim to animated webp:
+ *  (1) use ImageMagick to make a set of png files:
+ *      convert infile.gif -coalesce outroot_%03d.png
+ *  (2) read these files into a pixa, using
+ *      pixaReadFiles()
+ *  (3) write out the animated webp, selecting the duration and using
+ *      pixaWriteWebPAnim()
  * </pre>
  */