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VGA Fonts: Difference between revisions
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(Fixing some bugs and misinformed errors, general clean up) |
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Hint: use the same code as above, but swap source and destination for "rep movsd".
== Displaying a character ==
Okay, we have a font bitmap, but how to use it? Here's a simple example:
<source lang="c">
//this is the bitmap font you've loaded
unsigned char *font;
void drawchar(unsigned char c, int x, int y, int fgcolor, int bgcolor)
{
int cx,cy;
int mask[8]={1,2,4,8,16,32,64,128};
unsigned char *gylph=font+(int)c*8*16;
for(cy=0;cy<16;cy++){
for(cx=0;cx<8;cx++){
putpixel(glyph[cy]&mask[cx]?fgcolor:bgcolor,x+cx,y+cy);
}
}
}
</source>
It's not so complicated. You supply the function with arguments:
<pre>
c - the character's ASCII code you want to display
x,y - where to draw
fgcolor - foreground color
bgcolor - background color
</pre>
It could be handly to draw the background as well, because it erase the area under the glyph. But sometimes it could be annoying, so here's a slightly modificated version that's using transparent background:
<source lang="c">
//this is the bitmap font you've loaded
unsigned char *font;
void drawchar_transparent(unsigned char c, int x, int y, int fgcolor)
{
int cx,cy;
int mask[8]={1,2,4,8,16,32,64,128};
unsigned char *gylph=font+(int)c*8*16;
for(cy=0;cy<16;cy++){
for(cx=0;cx<8;cx++){
if(glyph[cy]&mask[cx]) putpixel(fgcolor,x+cx,y+cy);
}
}
}
</source>
As you can see, we only have one fgcolor this time. The putpixel call has a condition, only invoked if the bit in the bitmap is set. If it's clear, nothing will happen, thus makes the background transparent.
== See Also ==
* [[VGA Hardware]]
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