Misc/abrash-black-book
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James Gregory 2013-12-30 18:34:31 +11:00
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35-06.md
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@ -5,7 +5,7 @@
The result of all this is simply a single pixel drawn in the color set
up in **EVGALine**. **EVGADot** may seem excessively complex for a
function that does nothing more that draw one pixel, but programming the
VGA isn’t trivial (as we’ve seen in the early chapters of this part).
VGA isn't trivial (as we've seen in the early chapters of this part).
Besides, while the explanation of **EVGADot** is lengthy, the code
itself is only five lines long.
@ -25,7 +25,7 @@ hardware-dependent **outportb** lines in **EVGALine** itself.
**EVGALine** was that it would be ultimately used as the lowest-level
primitive of a graphics software package, with operations such as error
checking and clipping performed at a higher level. Similarly,
**EVGALine** is tied to the VGA’s screen coordinate system of (0,0) to
**EVGALine** is tied to the VGA's screen coordinate system of (0,0) to
(639,199) (in mode 0EH), (0,0) to (639,349) (in modes 0FH and 10H), or
(0,0) to (639,479) (in mode 12H), with the upper left corner considered
to be (0,0). Again, transformation from any coordinate system to the
@ -48,7 +48,7 @@ adjusted from one pixel to the next, rather than recalculated from
scratch.
These enhancements are not incorporated into the code in Listing 35.1
for a couple of reasons. One reason is that it’s important that the
for a couple of reasons. One reason is that it's important that the
workings of the algorithm be clearly visible in the code, for learning
purposes. Once the implementation is understood, rewriting it for
improved performance would certainly be a worthwhile exercise. Another
@ -60,9 +60,9 @@ times the speed?
Given which, a high-speed assembly language version of **EVGALine**
would seem to be a logical next step.
### Bresenham’s Algorithm in Assembly {#Heading11}
### Bresenham's Algorithm in Assembly {#Heading11}
Listing 35.3 is a high-performance implementation of Bresenham’s
Listing 35.3 is a high-performance implementation of Bresenham's
algorithm, written entirely in assembly language. The code is callable
from C just as is Listing 35.1, with the same name, **EVGALine**, and
with the same parameters. Either of the two can be linked to any program