Be a bit more type-safe about using libpng

The simplified libpng declarations in DarkPlaces just use "void **" for
various pointer-to-pointer arguments. However, this conflicts with the system
libpng headers (if used), which expect something like "png_struct **" (which
is not considered to be a compatible type by ISO C), causing compiler
warnings. This patch reduces the simplification a bit by distinguishing
between the various pointers-to-struct enough that system libpng headers
do not provoke warnings.

Similarly, assigning a function pointer provokes warnings if the arguments'
types are not exactly as expected. Avoiding those warnings potentially makes
genuine bugs easier to spot, so it seems worth being a bit more precise.

Origin: vendor, Debian

diff --git a/image_png.c b/image_png.c
index dc3554d7fc3722dfa046ce64355f84c110978763..a3afb3cc36d1fd99aabd8dbd2fc415c99192bdab 100644 (file)
--- a/image_png.c
+++ b/image_png.c
@@ -82,10 +82,15 @@ my_setjmp (jmp_buf env)
 
 #else
 
+typedef void *png_structp;
+typedef void **png_structpp;
+typedef void *png_infop;
+typedef void **png_infopp;
+
 static void                            (*qpng_set_sig_bytes)           (void*, int);
-static int                             (*qpng_sig_cmp)                         (const unsigned char*, size_t, size_t);
-static void*                   (*qpng_create_read_struct)      (const char*, void*, void(*)(void *png, const char *message), void(*)(void *png, const char *message));
-static void*                   (*qpng_create_write_struct)     (const char*, void*, void(*)(void *png, const char *message), void(*)(void *png, const char *message));
+static int                             (*qpng_sig_cmp)                         (unsigned char*, size_t, size_t);
+static void*                   (*qpng_create_read_struct)      (const char*, void*, void(*)(png_structp png, const char *message), void(*)(png_structp png, const char *message));
+static void*                   (*qpng_create_write_struct)     (const char*, void*, void(*)(png_structp png, const char *message), void(*)(png_structp png, const char *message));
 static void*                   (*qpng_create_info_struct)      (void*);
 static void                            (*qpng_read_info)                       (void*, void*);
 static void                            (*qpng_set_compression_level)   (void*, int);
@@ -102,7 +107,7 @@ static int                          (*qpng_set_interlace_handling)  (void*);
 static void                            (*qpng_read_update_info)        (void*, void*);
 static void                            (*qpng_read_image)                      (void*, unsigned char**);
 static void                            (*qpng_read_end)                        (void*, void*);
-static void                            (*qpng_destroy_read_struct)     (void**, void**, void**);
+static void                            (*qpng_destroy_read_struct)     (png_structpp, png_infopp, void**);
 static void                            (*qpng_destroy_write_struct)    (void**, void**);
 static void                            (*qpng_set_read_fn)                     (void*, void*, void(*)(void *png, unsigned char *data, size_t length));
 static void                            (*qpng_set_write_fn)            (void*, void*, void(*)(void *png, unsigned char *data, size_t length), void(*)(void *png));
@@ -306,7 +311,7 @@ static struct
 } my_png;
 
 //LordHavoc: removed __cdecl prefix, added overrun protection, and rewrote this to be more efficient
-static void PNG_fReadData(void *png, unsigned char *data, size_t length)
+static void PNG_fReadData(png_structp png, unsigned char *data, size_t length)
 {
        size_t l;
        l = my_png.tmpBuflength - my_png.tmpi;
@@ -323,21 +328,21 @@ static void PNG_fReadData(void *png, unsigned char *data, size_t length)
        //Com_HexDumpToConsole(data, (int)length);
 }
 
-static void PNG_fWriteData(void *png, unsigned char *data, size_t length)
+static void PNG_fWriteData(png_structp png, unsigned char *data, size_t length)
 {
        FS_Write(my_png.outfile, data, length);
 }
 
-static void PNG_fFlushData(void *png)
+static void PNG_fFlushData(png_structp png)
 {
 }
 
-static void PNG_error_fn(void *png, const char *message)
+static void PNG_error_fn(png_structp png, const char *message)
 {
        Con_Printf("PNG_LoadImage: error: %s\n", message);
 }
 
-static void PNG_warning_fn(void *png, const char *message)
+static void PNG_warning_fn(png_structp png, const char *message)
 {
        Con_Printf("PNG_LoadImage: warning: %s\n", message);
 }
@@ -346,7 +351,8 @@ unsigned char *PNG_LoadImage_BGRA (const unsigned char *raw, int filesize, int *
 {
        unsigned int c;
        unsigned int    y;
-       void *png, *pnginfo;
+       png_structp png;
+       png_infop pnginfo;
        unsigned char *imagedata = NULL;
        unsigned char ioBuffer[8192];
 
@@ -358,7 +364,8 @@ unsigned char *PNG_LoadImage_BGRA (const unsigned char *raw, int filesize, int *
                return NULL;
 #endif
 
-       if(qpng_sig_cmp(raw, 0, filesize))
+       // png_sig_cmp is not fully const-correct
+       if(qpng_sig_cmp((unsigned char *) raw, 0, filesize))
                return NULL;
        png = (void *)qpng_create_read_struct(
                (qpng_access_version_number() / 100 == 102) ? PNG_LIBPNG_VER_STRING_12 :
@@ -531,7 +538,8 @@ qboolean PNG_SaveImage_preflipped (const char *filename, int width, int height,
 {
        unsigned int offset, linesize;
        qfile_t* file = NULL;
-       void *png, *pnginfo;
+       png_structp png;
+       png_infop pnginfo;
        unsigned char ioBuffer[8192];
        int passes, i, j;
 
@@ -544,16 +552,16 @@ qboolean PNG_SaveImage_preflipped (const char *filename, int width, int height,
        }
 #endif
 
-       png = (void *)qpng_create_write_struct( 
-               (qpng_access_version_number() / 100 == 102) ? PNG_LIBPNG_VER_STRING_12 :
+       png = qpng_create_write_struct(
+               (qpng_access_version_number() / 100 == 102) ? PNG_LIBPNG_VER_STRING_12 : 
                (qpng_access_version_number() / 100 == 104) ? PNG_LIBPNG_VER_STRING_14 :
                (qpng_access_version_number() / 100 == 105) ? PNG_LIBPNG_VER_STRING_15 :
-               PNG_LIBPNG_VER_STRING_16, // nasty hack... whatever
+               PNG_LIBPNG_VER_STRING_16, // nasty hack to support both libpng12 and libpng14
                0, PNG_error_fn, PNG_warning_fn
        );
        if(!png)
                return false;
-       pnginfo = (void *)qpng_create_info_struct(png);
+       pnginfo = qpng_create_info_struct(png);
        if(!pnginfo)
        {
                 qpng_destroy_write_struct(&png, NULL);