VGA Fonts: Difference between revisions

And finally we came to the point where we can display a character. I'll assume you have a putpixel procedure ready.

We have to draw 8x16 pixels, one for every bit in the bitmap.

//this is the bitmap font you've loaded

unsigned char *font;

}

}

The arguments are straightforward. You may wonder why to subtract 12 from y. It's for the baseline: you specify y coordinate as the bottom of the character, not counting the "piggy tail" in a glyph that goes down (like in "p","g","q" etc.). I other words it's the most bottom row of letter "A" that has a bit set.

 

Although it's mostly useful to erase the screen under the glyph, in some cases it could be bad (eg.: writing on a shiny gradiented button). So here's a slightly modificated version, that uses a transparent background.

//this is the bitmap font you've loaded

unsigned char *font;

}

}

As you can see, we have only foreground color this time, and the putpixel call has a condition: only invoked if the according bit in the bitmap is set.

 

Of course the code above will be excruciatingly slow (mostly due to doing one pixel at a time, and repeatedly recalculating the address for each pixel within the "putpixel()" function). For much better performance, the code above can be optimised to use boolean operations and a "mask lookup table" instead. For example (for an 8-bpp mode):

 

//this is the bitmap font you've loaded

unsigned char *font;

}

}

 

In this case the address in display memory is only calculated once (rather than up to 128 times) and 8 pixels are done in parallel (which removes the inner loop completely).