Intel i86W Manual page 117

FLOATING·POINT INSTRUCTIONS
The interpolation operations of the i860 microprocessor support graphics applications in
which the set of points on the surface of a solid object is represented by polygons. The
distances and color intensities of the vertices of the polygon are known, but the distances
and intensities of other points must be calculated by interpolation between the known
values.
Certain fields of the
psr
are used by the i860 microprocessor's graphics instructions, as
illustrated in Figure 6-5.
The merge instructions are those that utilize the 64-bit MERGE register. The purpose of
the MERGE register is to accumulate (or merge) the results of multiple-addition oper-
ations that use as operands the color-intensity values from pixels or distance values from
a Z-buffer. The accumulated results can then be stored in one 64-bit operation.
Two multiple-addition instructions and an OR instruction use the MERGE register. The
addition instructions are designed to add interpolation values to each color-intensity
field in an array of pixels or to each distance value in a Z-buffer.
6.6.2.1 Z-8UFFER CHECK INSTRUCTIONS
A Z-buffer aids hidden-surface elimination by associating with a pixel a value that rep-
resents the distance of that pixel from the viewer. When painting a point at a specific
pixel location, three-dimensional drawing algorithms calculate the distance of the point
from the viewer.
If
the point is farther from the viewer than the point that is already
represented by the pixel, the pixel is not updated. The i860 microprocessor supports
distance values that are either 16-bits or 32-bits wide. The size of the Z-buffer values is
independent of the pixel size. Z-buffer element size is controlled by whether the 16-bit
instruction
fzchks
or the 32-bit instruction
fzchkl
is used; pixel size is controlled by the
PS field of the
psr.
31
PM
t
tL. ________
PIXEL SIZE
L. _____________
PIXEL MASK
240329i
Figure 6-5. PSR Fields for Graphics Operations
6-29