I use Photo Shop Elements to create my files. But any image editor that lets you create an image and type text into it will be fine.
GIMP has a text boxish option. At least in the GIMP on my Linux box, the Toolbox has a nice big 'A' and when I click on it, it lets me create a text box and type text in it.
It is common to split the file up into 16 characters per row.
And you want to have a clear background (transparent, nothing there) and the letters should be white so that they can accept the colors assigned with SetTextColor.
If, by some miracle, your font is a fixed width, then you don't need the subimages file, just make sure the file is 16 characters by 8 rows in the correct order for ascii values 128-255. And the character width must be divisible by 16 and the height by 8.
The image used for a character sets (of all types), is basically a file with the images ("<fontname>.png") and a subimages file that associates the ascii id with the piece of the image ("<fontname> subimages.txt", and the space after <fontname> is deliberate).
I've attached a sample image file.
The associated subimages file looks like this:
32:0:0:30:72
33:34:0:19:72
34:68:0:31:72
35:106:0:39:72
36:163:0:34:72
37:217:0:63:72
38:293:0:51:72
39:355:0:22:72
40:385:0:25:72
41:421:0:25:72
42:462:0:37:72
43:512:0:48:72
44:571:0:22:72
45:606:0:28:72
46:648:0:20:72
47:678:0:36:72
48:-2:88:43:72
49:59:87:27:72
50:111:87:40:72
51:167:88:40:72
52:221:87:45:72
53:278:88:39:72
54:333:88:43:72
55:391:87:40:72
56:445:88:42:72
57:502:88:42:72
58:558:88:20:72
59:590:88:22:72
60:627:88:44:72
61:687:88:47:72
62:750:88:44:72
63:811:88:33:72
64:-1:172:57:72
65:69:171:52:72
66:136:172:41:72
67:191:172:48:72
68:255:172:51:72
69:321:171:37:72
70:376:171:37:72
71:427:172:51:72
72:495:171:47:72
73:561:171:17:72
74:592:172:32:72
75:643:171:45:72
76:701:171:38:72
77:753:171:60:72
78:831:171:47:72
79:894:172:55:72
80:1:259:41:72
81:55:258:55:72
82:127:257:43:72
83:182:258:40:72
84:231:257:46:72
85:291:258:46:72
86:349:257:56:72
87:401:257:69:72
88:482:257:47:72
89:543:257:46:72
90:601:257:48:72
91:663:258:24:72
92:698:258:35:72
93:742:258:24:72
94:785:258:45:72
95:842:258:46:72
96:-2:344:24:72
97:39:343:38:72
98:95:343:43:72
99:152:343:38:72
100:203:343:44:72
101:263:343:42:72
102:317:344:33:72
103:358:344:43:72
104:420:344:40:72
105:479:344:17:72
106:501:344:27:72
107:551:344:40:72
108:600:344:24:72
109:640:344:60:72
110:719:344:40:72
111:775:343:48:72
112:1:428:43:72
113:59:428:43:72
114:121:428:26:72
115:161:428:34:72
116:206:428:31:72
117:253:428:40:72
118:308:428:43:72
119:361:428:61:72
120:433:428:36:72
121:486:428:44:72
122:538:428:39:72
123:589:428:27:72
124:633:428:15:72
125:664:428:27:72
126:705:428:47:72
127:748:428:0:0
The format for the subimages file is:
ascii code:starting X position:starting Y position:width:height
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master
