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Inside the ATI Pear Demo
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- The Pear Demo was written in OpenGL as a test application
for a variety of API features enabled by the Rage128.
Various incarnations of the Pear Demo have also been
used at a number of conferences including:
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Still shots from the Pear Demo will appear as cover
art and color plates in the forthcoming text Real-time
Rendering by Thomas Möller and Eric Haines, published
by A.
K. Peters.
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Visual Effects
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The Pear Demo demonstrates a variety of visual effects
including gloss mapping, specular mapping, mirror reflections
Specular & Gloss Mapping
Specular and gloss mapping add high quality specular highlights
to polygonal objects. A specular map is simply an environment
map that is added to the object, where bright patches
in the environment map correspond to the position of lights.
Gloss mapping is done in tha same manner, except that
a shininess channel is encoded in the base map. Prior
to the environment map being added to the object, it is
multiplied by the shininess. This results in varying shininess
across the object.
Mirror reflections
The Pear Demo shows reflections of the objects in the
chess board. This is accomplished by using a scaling matrix
to reflect the geometry of the objects through the plane
of the chess board when drawing the reflected objects.
The chess board is then drawn with an alpha blending equation
that computes src + srcAlpha * dst to give the impression
of variable reflectivity. The right side up objects are
then drawn normally. There are some good postings on this
topic to the comp.graphics.api.opengl
newsgroup written by Mark Kilgard and Tim Hall. The stencil
masking technique described in these postings is also
used in the Pear Demo.
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Controls
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[ESC] - Exit the demo
'1' - Diffuse lighting only
'2' - Diffuse lighting plus specular map
'3' - Diffuse lighting plus gloss map
'S' - Toggle scattering of the reflections
'U' - Toggles drawing the reflected objects
'E' - Toggles drawing the eraser
'C' - Toggles drawing the chess pieces
'N' - Toggles drawing the pencil
'P' - Toggles drawing the pear
'R' - Toggles the rotation on and off
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Downloads
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- Get the latest version of the Pear Demo for various
platforms here!
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