[devel] Revised pngvalid.c to test PNG_ALPHA_MODE_SUPPORTED correctly.

This allows pngvalid to build when ALPHA_MODE is not supported, which is
required if it is to build on libpng 1.4.

ANNOUNCE

@@ -169,7 +169,12 @@ Version 1.5.3beta11 [June 11, 2011]
     IDE autogenerates appropriate makefiles (libpng.mk) for batch processing.
     The project is configurable, unlike the Visual Studio project, so long
     as the developer has an awk.
-  Improved gamma range checks and other things OpenWatcom warns about.
+  Changed png_set_gAMA to limit the gamma value range so that the inverse
+    of the stored value cannot overflow the fixed point representation,
+    and changed other things OpenWatcom warns about.
+  Revised pngvalid.c to test PNG_ALPHA_MODE_SUPPORTED correctly. This allows
+    pngvalid to build when ALPHA_MODE is not supported, which is required if
+    it is to build on libpng 1.4.
 
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CHANGES

@@ -3432,7 +3432,12 @@ Version 1.5.3beta11 [June 11, 2011]
     IDE autogenerates appropriate makefiles (libpng.mk) for batch processing.
     The project is configurable, unlike the Visual Studio project, so long
     as the developer has an awk.
-  Improved gamma range checks and other things OpenWatcom warns about.
+  Changed png_set_gAMA to limit the gamma value range so that the inverse
+    of the stored value cannot overflow the fixed point representation,
+    and changed other things OpenWatcom warns about.
+  Revised pngvalid.c to test PNG_ALPHA_MODE_SUPPORTED correctly. This allows
+    pngvalid to build when ALPHA_MODE is not supported, which is required if
+    it is to build on libpng 1.4.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

pngvalid.c

@@ -6401,7 +6401,9 @@ gamma_component_validate(PNG_CONST char *name, PNG_CONST validate_info *vi,
 
       if (alpha < 0) /* The alpha channel */
       {
+#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
          if (do_background != ALPHA_MODE_OFFSET + PNG_ALPHA_BROKEN)
+#endif
          {
             /* In all other cases the output alpha channel is linear already,
              * don't log errors here, they are much larger in linear data.
@@ -6411,6 +6413,7 @@ gamma_component_validate(PNG_CONST char *name, PNG_CONST validate_info *vi,
          }
       }
 
+#ifdef PNG_READ_ALPHA_MODE_SUPPORTED
       else /* A component */
       {
          if (do_background == ALPHA_MODE_OFFSET + PNG_ALPHA_OPTIMIZED &&
@@ -6420,6 +6423,7 @@ gamma_component_validate(PNG_CONST char *name, PNG_CONST validate_info *vi,
             output_is_encoded = 0;
          }
       }
+#endif
 
       if (output_is_encoded)
          output = pow(output, vi->screen_gamma);