Simple VGA text question

xsmoker

Hey, new to the forum, prop and I'm curious is there a easy way to change screen text size from 128 X 64 characters down to something the size of 64 across by 16 down?

Thankx

Rayman

The internal font is fixed at 16x32 pixels. So, how many characters depends mostly on your choice of driver... There are VGA, XGA, SXGA, and UGA drivers about (see Object Exchange).·

I'm assuming you mean for VGA and not TV...

Mike Green

There are several different VGA drivers and some of them have different screen sizes. 128 x 64 is the largest provided by one particular driver. This driver (VGA High-Res Text) is configurable to smaller screen sizes like 100 x 50 and 80 x 40 by commenting out the set of parameters used for 128 x 64 and uncommenting the ones for 80 x 40. There's a 64 x 48 driver posted as the VGA_Tile_Hydra_Demo that can mix small areas of graphics with text without the high memory overhead of a full screen of bit-mapped graphics.

xsmoker

Well with a 1024X768 driver that is setup with 64x24, I was able to change the virtical pixels to 512 from 768 and I offset the vertical front porch lines from 3 to 259. Then I changed the number of rows that was set up from 48 (24 lines) to 32 (16 lines).

This works and the scrolling works great but the result is half a screen. Anything else I can change to stretch it vertically?

Mike Green

Since all of the vertical timing is directly under control of the driver code, you could just double up the horizontal scan lines. In other words, change the code at the end of the line to go back and do the identical processing for another scan line before you increment the font line or text address.

xsmoker

I guess that is where I need the help. The driver I am trying to mod is the VGA 1024X768 driver with cursor. I don't need the cursor, or even color. The original setup was 64 X 24 so I can't double the 16 lines I'm using now, there isn't enough hz lines to do that.

I split the extra vertical pixal lines more evenly between the vertical front porch and the back porch and that has moved the 64 X 16 window down to the center. Somehow I would like to change the vsync timing.

Mike Green

I can't help you. This is a really complicated driver because it's so tight on space and time and requires that the cogs remain synchronized. Somehow you need to add a delay after each horizontal line so that the 512 scan lines take the same time as the undelayed 768 scan lines would normally take at full speed, yet the horizontal scan line has to remain otherwise unaffected. You might have better luck starting with one of the other drivers.