fix g2c_dec_png and make png grid size configurable

CMakeLists.txt

@@ -70,6 +70,9 @@ if(USE_PNG)
   find_package(ZLIB REQUIRED)
   find_package(PkgConfig REQUIRED)
   find_package(PNG REQUIRED)
+  set(PNG_WIDTH_MAX 100000000 CACHE STRING "Default width of PNG grid.")
+  set(PNG_HEIGHT_MAX 100000 CACHE STRING "Default height of PNG grid.")
+  message(STATUS "\tWill build with PNG grid width = ${PNG_WIDTH_MAX} and height = ${PNG_HEIGHT_MAX}")
 else()
   message(STATUS "Will not build PNG support")
 endif()

src/decenc_png.c

@@ -100,7 +100,15 @@ int
 g2c_dec_png(unsigned char *pngbuf, int *width, int *height,
             unsigned char *cout)
 {
-    return dec_png(pngbuf, (g2int *)&width, (g2int *)&height, cout);
+    g2int width8 = *width, height8 = *height;
+    int ret;
+
+    ret = dec_png(pngbuf, (g2int *)&width, (g2int *)&height, cout);
+
+    *width = (g2int)width8;
+    *height = (g2int)height8;
+
+    return ret;
 }
 
 /**
@@ -165,6 +173,9 @@ dec_png(unsigned char *pngbuf, g2int *width, g2int *height,
     /* Read and decode PNG stream. */
     png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
 
+/*     support for larger grids   */
+    png_set_user_limits(png_ptr, G2C_PNG_WIDTH_MAX, G2C_PNG_HEIGHT_MAX);
+
     /* Get pointer to each row of image data. */
     row_pointers = png_get_rows(png_ptr, info_ptr);
 

src/grib2.h.in

@@ -423,6 +423,8 @@ int g2c_param_all(int param_idx, int *g1ver, int *g1val, int *g2disc, int *g2cat
 
 #define G2C_JASPER_MAX_MEM @JASPER_MAX_MEM@ /**< Maximum size for the Jasper memory buffer. */
 
+#define G2C_PNG_WIDTH_MAX @PNG_WIDTH_MAX@ /**< Maximum width of PNG grid */
+#define G2C_PNG_HEIGHT_MAX @PNG_HEIGHT_MAX@ /**< Maximum height of PNG grid */
 /* Error codes for G2 API. */
 #define G2_NO_ERROR 0             /**< Function succeeded. */
 #define G2_CREATE_GRIB_VERSION -1 /**< Wrong GRIB version for g2_create(), must be 2. */