High Resolution Video Modes Only Support 30 or 60 Text Lines

ID Number: Q71263

5.10 6.00 6.00a

MS-DOS

Summary:

When using the graphics library to write text to the screen, you can

select the number of rows to be displayed based on the capabilities of

the monitor with which you are working. For instance, when you are

working on a VGA monitor in text mode, you can call _settextrows()

with either 25, 43, or 50 lines. When in graphics mode, these numbers

are limited to either 30 or 60 lines.

The reason for these limitations is strictly a matter of the size of

the screen in pixels for the graphics mode selected. When you select

one of the high-resolution VGA graphics modes (_VRES2COLOR or

_VRES16COLOR), you are actually switching to video mode 11 or 12. In

these modes, you have a resolution of 640 pixels across and 480 pixels

down (640x480).

There are basically two fonts built into the VGA BIOS. They are both 8

pixels wide and either 8 or 16 pixels high (8x8 and 8x16). When

matched to a vertical resolution of 480 pixels, this equals 30 lines

of text in the case of the 8x16 font and 60 lines in the case of the

8x8 font.