Add indication of offending cell in C64 formats

src/miscfileformats.c

@@ -2831,9 +2831,8 @@ int Save_C64_hires(T_IO_Context *context, char *filename, byte saveWhat, byte lo
             numcolors=Count_used_colors_area(cusage,cx*8,cy*8,8,8);
             if (numcolors>2)
             {
-                Warning_message("More than 2 colors in 8x8 pixels");
+                Warning_with_format("More than 2 colors\nin 8x8 pixel cell: (%d, %d)\nRect: (%d, %d, %d, %d)", cx, cy, cx * 8, cy * 8, cx * 8 + 7, cy * 8 + 7);
                 // TODO here we should hilite the offending block
-                printf("\nerror at %dx%d (%d colors)\n",cx*8,cy*8,numcolors);
                 return 1;
             }
             c1 = 0; c2 = 0;
@@ -3006,7 +3005,7 @@ int Save_C64_multi(T_IO_Context *context, char *filename, byte saveWhat, byte lo
 			numcolors=Count_used_colors_area(cusage,cx*4,cy*8,4,8);
 			if(numcolors>4)
 			{
-				Warning_message("More than 4 colors in 4x8");
+				Warning_with_format("More than 4 colors\nin 4x8 pixel cell: (%d, %d)\nRect: (%d, %d, %d, %d)", cx, cy, cx * 4, cy * 8, cx * 4 + 3, cy * 8 + 7);
 				// TODO hilite offending block
 				return 1;
 			}

src/windows.c

@@ -25,6 +25,7 @@
 */
 
 #include <math.h>
+#include <stdarg.h> // va_args ...
 #include <stdlib.h> // atoi()
 #include <string.h> // strncpy() strlen()
 
@@ -1183,6 +1184,26 @@ void Warning_message(char * message)
   Display_cursor();
 }
 
+/// Window that shows a warning message and waits for a click on the OK button
+/// This has the added advantage of supporting the printf interface.
+void Warning_with_format(const char *template, ...) {
+  va_list arg_ptr;
+  char *message;
+
+  message = malloc(sizeof(char) * 1024);  // a maximum of 1 KiB of complete message.
+  if (message) {
+    va_start(arg_ptr, template);
+    vsprintf(message, template, arg_ptr);
+    //Warning_message(message);
+    Verbose_message("Warning", message);
+    va_end(arg_ptr);
+    free(message);
+  } else {
+    //Warning_message(template);
+    Verbose_message("Warning", template);
+  }
+}
+
 /// Window that shows a big message (up to 35x13), and waits for a click on OK.
 /// On call: Cursor must be displayed
 /// On exit: Cursor is displayed

src/windows.h

@@ -76,6 +76,7 @@ void Print_counter(short x,short y,const char * str,byte text_color,byte backgro
 
 byte Confirmation_box(char * message);
 void Warning_message(char * message);
+void Warning_with_format(const char * message, ...);
 void Verbose_message(const char * caption, const char * message);
 int Requester_window(char* message, int initial_value);