This is a  patch file for "libpng" 1.6.37.  "libpng" 1.6.37 omits some
legacy functions and/or  access  to some internal functions,  and this
breaks various programs. This patch file restores the  following func-
tions and/or access to the functions:

      png_check_sig
      png_read_data
      png_set_dither
      png_set_gray_1_2_4_to_8

--- libpng-1.6.37.old/png.c
+++ libpng-1.6.37/png.c
@@ -36,6 +36,38 @@
 #define GCC_STRICT_OVERFLOW 0
 #endif
 
+//--------------------------------------------------------------------
+
+#ifdef PNG_READ_SUPPORTED
+#undef png_check_sig
+
+int PNGAPI
+png_check_sig (png_bytep sig, int num)
+{
+  return ((int) !png_sig_cmp (sig, (png_size_t) 0, (png_size_t) num));
+}
+#endif
+
+/* Read the data from whatever input you are using.  The default routine
+ * reads from a file pointer.  Note that this routine sometimes gets called
+ * with very small lengths, so you should implement some kind of simple
+ * buffering if you are using unbuffered reads.  This should never be asked
+ * to read more then 64K on a 16 bit machine.
+ */
+
+#ifdef PNG_READ_SUPPORTED
+void PNGAPI
+png_read_data (png_structp png_ptr, png_bytep data, png_size_t length)
+{
+   if (png_ptr->read_data_fn != NULL)
+      (*(png_ptr->read_data_fn)) (png_ptr, data, length);
+   else
+      png_error (png_ptr, "Call to NULL read function");
+}
+#endif
+
+//--------------------------------------------------------------------
+
 /* Tells libpng that we have already handled the first "num_bytes" bytes
  * of the PNG file signature.  If the PNG data is embedded into another
  * stream we can set num_bytes = 8 so that libpng will not attempt to read
--- libpng-1.6.37.old/png.h
+++ libpng-1.6.37/png.h
@@ -905,6 +905,12 @@
  */
 PNG_EXPORT(2, void, png_set_sig_bytes, (png_structrp png_ptr, int num_bytes));
 
+/* Restored access to legacy functions */
+PNG_EXPORT (2, int, png_check_sig, (png_bytep, int));
+PNG_EXPORT (1, void, png_set_gray_1_2_4_to_8, (png_structp));
+PNG_EXPORT (3, void, png_read_data,
+    (png_structp, png_bytep, png_size_t));
+
 /* Check sig[start] through sig[start + num_to_check - 1] to see if it's a
  * PNG file.  Returns zero if the supplied bytes match the 8-byte PNG
  * signature, and non-zero otherwise.  Having num_to_check == 0 or
--- libpng-1.6.37.old/pngpriv.h
+++ libpng-1.6.37/pngpriv.h
@@ -1,4 +1,3 @@
-
 /* pngpriv.h - private declarations for use inside libpng
  *
  * Copyright (c) 2018-2019 Cosmin Truta
@@ -1087,10 +1086,6 @@
 PNG_INTERNAL_FUNCTION(png_uint_32,png_read_chunk_header,(png_structrp png_ptr),
    PNG_EMPTY);
 
-/* Read data from whatever input you are using into the "data" buffer */
-PNG_INTERNAL_FUNCTION(void,png_read_data,(png_structrp png_ptr, png_bytep data,
-    size_t length),PNG_EMPTY);
-
 /* Read bytes into buf, and update png_ptr->crc */
 PNG_INTERNAL_FUNCTION(void,png_crc_read,(png_structrp png_ptr, png_bytep buf,
     png_uint_32 length),PNG_EMPTY);
--- libpng-1.6.37.old/pngrio.c
+++ libpng-1.6.37/pngrio.c
@@ -1,4 +1,3 @@
-
 /* pngrio.c - functions for data input
  *
  * Copyright (c) 2018 Cosmin Truta
@@ -21,25 +20,6 @@
 #include "pngpriv.h"
 
 #ifdef PNG_READ_SUPPORTED
-
-/* Read the data from whatever input you are using.  The default routine
- * reads from a file pointer.  Note that this routine sometimes gets called
- * with very small lengths, so you should implement some kind of simple
- * buffering if you are using unbuffered reads.  This should never be asked
- * to read more than 64K on a 16-bit machine.
- */
-void /* PRIVATE */
-png_read_data(png_structrp png_ptr, png_bytep data, size_t length)
-{
-   png_debug1(4, "reading %d bytes", (int)length);
-
-   if (png_ptr->read_data_fn != NULL)
-      (*(png_ptr->read_data_fn))(png_ptr, data, length);
-
-   else
-      png_error(png_ptr, "Call to NULL read function");
-}
-
 #ifdef PNG_STDIO_SUPPORTED
 /* This is the function that does the actual reading of data.  If you are
  * not reading from a standard C stream, you should create a replacement
--- libpng-1.6.37.old/pngrtran.c
+++ libpng-1.6.37/pngrtran.c
@@ -31,6 +31,16 @@
 
 #ifdef PNG_READ_SUPPORTED
 
+/* Expand grayscale images of less than 8-bit depth to 8 bits. */
+/* Deprecated as of libpng-1.2.9 */
+
+void PNGAPI
+png_set_gray_1_2_4_to_8 (png_structp png_ptr)
+{
+   if (png_ptr == NULL) return;
+   png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
+}
+
 /* Set the action on getting a CRC error for an ancillary or critical chunk. */
 void PNGAPI
 png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)