Misc/abrash-black-book
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James Gregory 2013-12-30 18:34:31 +11:00
commit 18011c595a
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23-04.md
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@ -4,7 +4,7 @@
#### Smooth Panning {#Heading7}
The first thing you’ll notice upon running the sample program is the
The first thing you'll notice upon running the sample program is the
remarkable smoothness with which the display pans from side-to-side and
up-and-down. That the display can pan at all is made possible by two VGA
features: 256K of display memory and the virtual screen capability. Even
@ -73,7 +73,7 @@ register, AC register 13H, working in conjunction with the start
address. Up to 7 pixels worth of single pixel panning of the displayed
image to the left is performed by increasing the Horizontal Pel Panning
register from 0 to 7. This exhausts the range of motion possible via the
Horizontal Pel Panning register; the next pixel’s worth of smooth
Horizontal Pel Panning register; the next pixel's worth of smooth
panning is accomplished by incrementing the start address by one and
resetting the Horizontal Pel Panning register to 0. Smooth horizontal
panning should be viewed as a series of fine adjustments in the 8-pixel
@ -82,7 +82,7 @@ range between coarse byte-sized adjustments.
A horizontal panning oddity: Alone among VGA modes, text mode (in most
cases) has 9 dots per character clock. Smooth panning in this mode
requires cycling the Horizontal Pel Panning register through the values
8, 0, 1, 2, 3, 4, 5, 6, and 7. 8 is the “no panning” setting.
8, 0, 1, 2, 3, 4, 5, 6, and 7. 8 is the "no panning" setting.
There is one annoying quirk about programming the AC. When the AC Index
register is set, only the lower five bits are used as the internal