Calculating Alpha Character Values Characters in the range 00-FF hex (0-255 decimal) use their normal Unicode values. Note that the position of some characters is different from their ASCII value and/or their value assigned b the TELETEXT standard. Add E000 hex (57344 decimal) to the original char for Double Height - Upper, and add E100 hex (57600 decimal) for Double Height - Lower. For example, to display a double height capital A, which has the code 41 hex (65 decimal), use the codes E041 and E141 hex (57409 and 57665 decimal): E041 = 41 + E000  E151 = 41 + E10057409 = 65 + 57344  57665 = 65 + 57600Calculating Graphic Block Char Values The 64 standard graphics blocks start at E200 hex (57856 decimal). Each block is character into 6 blocks. Add on these values for each block that is on: HexDecimal 1 2 1 2 4 8 4 810201632 For example the code for character  is E219 hex (57881 decimal): E219 = E200 + 1 + 8 + 1057881 = 57856 + 1 + 8 + 16 Add on 40 hex (64 decimal) for Double Height Upper characters, and 80 hex (128 decimal) for Double Height Lower. For separated graphic characters add on C0 hex (192 decimal). This can be com- bined with double height. For example to display the character  in double height and separated, use the codes E319 and E359 hex (58137 and 58201 decimal): E319 = E219 + 40 + C0  E359 = E219 + 80 + C058137 = 57881 + 64 + 192  58201 = 57881 + 128 + 192 Note that the TELETEXT standard uses 64 (40 hex) for the value of the lower right pixel within the graphics block when calculating graphics characters. A Few Notes The Font was based on ModeSeven by Andrew Bulhak. I added the double height characters, all of the various graphics blocks, and fixed a few errors. I created this because I couldn't find a free font that included the graphics block characters, someone might have created one before though. The advantage of this approach over one that uses images for each of the graphics characters is that the font file itself is relatively small, and the browser doesn't have to download many hundreds of small images. Teletext pages are often rendered as a single image, but the problem with that is that the text can't be copied, searched, or indexed- it's more hassle to maintain than simple static HTML fiiles too. The main negative aspect of my approach (using a font over images) is that sup- port for the @font-face attribute is still a bit patchy. This page should work fine in modern browsers however. This stylesheet allows characters to be arranged in many ways which would be impossible in the standard Mode 7 Teletext screen. For example, the character that changes the foreground colour causes a space in the page, and changing the background colour causes two spaces. If you are looking to recreate an authentic Teletext web page you must pay attention to these limit- ations. Mode 7 is 25 rows of 40 characters. The first character on each row is usually blank, which allows first character to be use to set the foreground or back- ground colour on any row while still aligning the left edge of the text. The values of the graphical characters in the Teletext character set can also be calculated by assigning a power of 2 to each of the 6 sub-blocks, but the bottom right sub-block is assigned 64 where I used 32. If you are crazy enough to do the calc- ulations by hand as I did for this page, you will find performing the calculations in hex much simpler than in decimal- the examples above should be enough to demonstrate this. I added the decimal equivalents for people who aren't interested in learning to count in hexadecimal just to use this font. Using this font and stylesheet you can do things that are illegal within the TELETEXT standard, such as two-colour double height text (which the BBC Micro's MODE 7 allows too), black fore- ground, and instant changes of back- ground and foreground colours that would require empty spaces on a TELETEXT page or MODE 7 screen. This font is free to use in non- commercial projects. I would appreciate a credit and notification that you are using it. Let me know if you see any errors, or have any other feedback! Teletext font by 3d@galax.xyz 2014 HomeTopStaticEmail