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framebuffer colors

From frank.n. dale

Answered By: Thomas Adam

Hello Gang,

Assume X is not running and your framebuffer allows for 256 colors or more.

Please give manual instructions (or C code) to write on the screen 64 characters in different colors.

[Thomas] Hi, there. Assume for a moment that we cared. Then realise that actually this is The Answer Gang to do with Linux questions. Then assume that we do not answer homework questions. Then assume that you want to look here:

https://linuxgazette.net/tag/ask-the-gang.html

If you assume all of these, then you have a tautology.

Of course your programming homework is quite easy to do, it just requires that you do a little research first, as with any academic course you might be studying. It takes work, and if you are not prepared to put any in, why bother with it? If you do not understand it, then that is a different matter, to be taken up with your lecturer.

Please do not forward this query to Thomas Adam, he does not know.

[Thomas] Unfortunately, I do.

How do you set and get colors outside the range 0-F hex when using framebuffer in the Linux console?

[Thomas] For this, you will have to look at vga.c in the kernel source, and at fb.c. You will almost certainly have to hack the kernel source to allow this.

This query is not a home work exercise. It is based on fruitless Goggle search of many hours over a span of several months. The major framebuffer sites

https://linuxconsole.sourceforge.net/fbdev https://linux-fbdev.sourceforge.net https://www.directfb.org

do not deal with it nor does the HOWTO-framebuffer. Also the console escape sequences for colors only apply to colors 0-F.

The only solution found so far involves the SVGALib which is too much of an overhead. There must be a simpler solution. Do you know more than I do?

[Thomas] SVGALib is nothing to do with framebuffers, but it will allow you to display console screen resolutions higher than the default.

The query is relevant for syntax coloring in the Linux console (text, no X). With the standard 16 foreground and 8 background colors, syntax coloring is a pain in the eyes. With the 256 colors or more that you get from framebuffer, syntax coloring could become pleasant and effective.

[Thomas] So why not run your console with a setting of:

vga=0x317

while will run a 1024x786x256 colours.

Look here:

Colours   640x400 640x480 800x600 1024x768 1152x864 1280x1024 1600x1200
--------+--------------------------------------------------------------
 4 bits |    ?       ?     0x302      ?        ?        ?         ?
 8 bits |  0x300   0x301   0x303    0x305    0x161    0x307     0x31C
15 bits |    ?     0x310   0x313    0x316    0x162    0x319     0x31D
16 bits |    ?     0x311   0x314    0x317    0x163    0x31A     0x31E
24 bits |    ?     0x312   0x315    0x318      ?      0x31B     0x31F
32 bits |    ?       ?       ?        ?      0x164      ?

(this is for: vga=<foo> in /etc/lilo.conf).

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