From: lupe@ukw.uucp (Lupe Christoph)
Newsgroups: comp.sys.sun.hardware
Subject: Re: SPARCstation 10 Graphics Options
Date: 21 Nov 92 08:44:57 GMT
Organization: cic

winter@sol.surv.utas.edu.au (Derek Winter) writes:

>Hello All,

>Investigating the options available for the SPARC 10 series, there are 4
>different Graphics Accelerator chips which can be used. In the advertising
>these are outlined as shown below, BUT this does not mean a great deal to me.
>Could some one please explain what the asterisked (*) terms mean, and what
>practical significance they have? i.e. what real benefits are there from moving
>from GX -> GXPlus -> GS -> GT?

I'm no graphics buff, so I beg those who are for forgiving
mistake I make.

First, a short version:

GX	is your standard 2D accelerator. 3D is done in software.
GXPlus	is a double buffering version, to be used in animation.
GS	is Sun's cheapest 3D accelerator. It fits into a pizza
	box, but just barely.
GT	is Sun's high-end 3D accelerator. It has a box of it's
	own, coupled to the SBus.

>Here are the options... 

>                GX      8bit 2D/3D wireframe(*)
>                        1152x900 resolution

Wireframe means you draw 3D models as if the model has
been built with wires, i.e. the surfaces are missing.

>		GXPlus  8bit 2D/3D wireframe
>                        1280x1024 resolution
>                        hardware double buffering(*)

Double buffering means you have in essence two framebuffers,
one to draw into, while the other one is displayed. When you
are done drawing, you switch. This way the updates are invisible.
Of course, you can also draw into the the framebuffer that
is being displayed. Then you just loose the advantage of the
double buffering.

>                GS      24bit 3D solids(*)
>                        1152x900 resolution
>                        double buffering
>                        Z-buffer(*)
>                        Gouraud shading(*)
>                        Depth cueing(*)

Solids means surfaces are drawn.

A Z buffer is used for hidden surface removal. You store the
distance from the "front" of each pixel into it. when you draw
a pixel, you check if it's in front of the one already drawn
or behind it.

Gouraud shading is used to curved surfaces. The simplest way
to do shading (i.e. show effects from light sources) is flat
shading. Each surface has the same color in each pixel. Gouraud
shading (if my memory serves me) interpolates the pixel colors
between the edges of the polygon. There is also Phong shading
(and probably many more I never heard about). Phong shading
computes the pixel color from the lighting at each point.
Very compute intensive.

Depth cueing means that you help the eye to judge the distance
of a point by making those near to the front lighter in color
and those distant darker.

>                GT      24bit 3D solids
>                        1280x1024 resolution
>                        double buffering
>                        Z-buffer
>                        Gouraud shading
>                        Depth cueing
>                        Transparency(*)
>                        Anti-aliasing(*)
>                        Overlays(*)

I'm not sure what they mean with transparency here, but I guess
they mean you can have overlay planes that are "switched off"
at individual pixels.

Anti-aliasing is used to prevent "jaggies". If you draw a line
that is not exactly vertical or horizontal, you will get a jagged
sequence of pixels (same is true for any non-linear line, e.g.
a circle). Now anti-aliasing puts pixels of a blend of the line
color and the background color next to those pixels. The effect is
that the line looks a bit fuzzy to the eye, but not jagged any more.

Overlays or overlay planes are used to combine things like the cursor
or text with the grphics in the normal planes. Imagine you have a
doctor who will draw a ring around a part of a computer tomography
image to highlight something he found. You do this ring in an overlay
plane to retain the original pixels. But they are obscured by the
pixels of the ring.
-- 
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| lupe@ukw.UUCP       (German EUNet, domain)     |  As I am self-employed, |
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| Res non sunt complicanda praeter necessitatem. |  of my employer.        |