better display of error messages

funcs/fimg-png.c

@@ -10,6 +10,25 @@
 
 #include "../floatimg.h"
 
+/* --------------------------------------------------------------------- */
+static char *pngerr2str(int code)
+{
+switch (code)	{
+	case	1:			return "Done";
+	case	0:			return "No error";
+	case	-1:			return "File error";
+	case	-2:			return "Header error";
+	case	-3:			return "IO error";
+	case	-4:			return "EOF error";
+	case	-5:			return "CRC error";
+	case	-6:			return "Memory error";
+	case	-7:			return "Zlib error";
+	case	-8:			return "Unknow filter";
+	case	-9:			return "Not supported";
+	case	-10:			return "Wrong arguments";
+	}
+return "*unknow*";
+}
 /* --------------------------------------------------------------------- */
 /*
  *	warning : this func has been tested only with
@@ -26,12 +45,16 @@ int		datasize;
 fprintf(stderr, ">>> %-25s ( '%s' %p )\n", __func__, filename, fimg);
 #endif
 
+/*	We MUSTclear the fimg destination header first */
+memset(fimg, 0, sizeof(FloatImg));
+
 memset(&png, 0, sizeof(png_t));
 png_init(NULL, NULL);			/* this is VITAL ! */
 
 foo = png_open_file_read(&png, filename);
 if (PNG_NO_ERROR != foo) {
-	fprintf(stderr, "%s open_file '%s' -> %d\n", __func__, filename, foo);
+	fprintf(stderr, "%s :\n\topen_file '%s' = %d %s\n", __func__,
+			filename, foo, pngerr2str(foo));
 	return foo;
 	}
 #if DEBUG_LEVEL > 1
@@ -70,8 +93,8 @@ if (foo) {
 
 foo = png_get_data(&png, datas);
 if (PNG_NO_ERROR != foo) {
-	fprintf(stderr, "error in '%s' : read png -> %d\n",
-						__func__, foo);
+	fprintf(stderr, "error in '%s' : read png -> %d %s\n",
+			__func__, foo, pngerr2str(foo));
 	return foo;
 	}
 
@@ -138,6 +161,7 @@ if (PNG_NO_ERROR != foo) {
 						__func__, foo);
 	return foo;
 	}
+
 ptr = datas;
 for (idx=0; idx<png.width * png.height; idx++) {
 	fimg->R[idx] = (float)*ptr++;