Index: tools/convbdf.c
===================================================================
--- tools/convbdf.c	(Revision 20153)
+++ tools/convbdf.c	(Arbeitskopie)
@@ -487,7 +487,11 @@
             return 0;
         }
         if (isprefix(buf, "STARTCHAR")) {
-            encoding = width = bbw = bbh = bbx = bby = -1;
+            encoding = width = -1;
+            bbw = pf->fbbw;
+            bbh = pf->fbbh;
+            bbx = pf->fbbx;
+            bby = pf->fbby;
             continue;
         }
         if (isprefix(buf, "ENCODING ")) {
@@ -519,6 +523,7 @@
         if (strequal(buf, "BITMAP") || strequal(buf, "BITMAP ")) {
             bitmap_t *ch_bitmap = pf->bits + ofs;
             int ch_words;
+            int y;
 
             if (encoding < 0)
                 continue;
@@ -550,6 +555,19 @@
 #define BM(row,col)	(*(ch_bitmap + ((row)*ch_words) + (col)))
 #define BITMAP_NIBBLES	(BITMAP_BITSPERIMAGE/4)
 
+            if (bby < -pf->descent) {
+                fprintf(stderr, "Warning: character %d goes %d pixel(s)"
+                        " beyond the font's descent, it will be clipped\n",
+                        encoding, -bby-pf->descent);
+            }
+            if (bby + bbh > pf->ascent) {
+                fprintf(stderr, "Warning: character %d goes %d pixel(s)"
+                        " beyond the font's ascent, it will be clipped\n",
+                        encoding, bby + bbh - pf->ascent);
+            }
+
+            y = bby + bbh; /* 0-based y within the char */
+            
             /* read bitmaps*/
             for (i=0; ; ++i) {
                 int hexnibbles;
@@ -560,6 +578,12 @@
                 }
                 if (isprefix(buf, "ENDCHAR"))
                     break;
+                
+                y--;
+                if ((y >= pf->ascent) || (y < -pf->descent)) {
+                    /* We're beyond the area that Rockbox can render -> clip */
+                    continue;
+                }
 
                 hexnibbles = strlen(buf);
                 for (k=0; k<ch_words; ++k) {