[SDL] Re: Truetype vs bitmapped fonts? Opinions?
Frank J. Ramsay
framsay at interactive.com
Tue Apr 11 13:11:22 PDT 2000
No, it's not RLE compression... the author of the book refers to it
as LLE compression. I'll _try_ and explain it.
If a scanline of the bitmap is:
- completely transparent just store a single '0' for it
- completely solid, store a 1 followed by the line data
- a mix of solid and transparent information store:
- The number of 'runs' (a run being a series of either
solid pixels) + 1
- then the decompressed offset of each run
- then the length of each run.
- then the data for the solid runs.
(I don't remember how the transparent parts are
decoded, but it works)
So when it is blitted, if it the loop hits a '0' for the first byte
of the line it just skips the line. If it hits a '1' it just memcpy
the entire row. If it his a number greater than 1, it blits each run
seperatly with a memcpy.
While this may sound slow, it's a lot faster than checking each
> You mean RLE compression? I'm talking not about one transparency value for
> all surface, but about transparecy value for each non-color-keyed pixel,
> and i'm curios is this supported by hardware or must be written by hand.
> On Tue, 11 Apr 2000, Frank J. Ramsay wrote:
> > Remember 16bpp color is the same (on the surface) as a Uint16, so you
> > can compare it to a Uin16 value. However in the book, "Real Time
> > Stragegy Game Programming using MS DX6" there is a great example of how
> > to compress 16bpp sprite. This method has a great feature of
> > compressing out transparent parts of the image.
> > -fjr
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