This section provides the details for several of HP's rendering
capabilities. These rendering capabilities range from the way HP
implements its default visuals to the way HP deals with the decomposition
of concave quadrilaterals.
Default Visuals |
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Instead of placing the default visual in the deepest image
buffer, HP puts the default visual in the overlay planes.
EXP and EXP2 Fogging |
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The Virtual Memory Driver's implementation of fog applies
fog per fragment. Hardware devices implement EXP and EXP2
fog per fragment and linear fog per vertex.
Bow-Tie Quadrilaterals |
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A quadrilateral has four vertices that are coplanar. When
this quadrilateral is twisted and you look at a front view of it
on the display, there appears to be a fifth vertex. This fifth vertex
which is not a true vertex will have no attributes, therefore, the
color at what appears to be the intersection of two lines will in
most cases be different from what is expected. HP treats the two
parts of the bow tie as two separate triangles that have attributes
assigned to their vertices. This special rendering process takes
care of the color problem at the non-existent fifth vertex.
To learn how other implementations of OpenGL deal with bow-tie
quadrilaterals, read the section "Describing Points, Lines, and
Polygons" in Chapter 2 of the OpenGL Programming Guide.
Decomposition of Concave Quadrilaterals |
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HP determines whether the concave quadrilateral will become
front facing or back-facing prior to dividing the quadrilateral
into triangles. HP then divides the surface into two triangles between
vertices zero and two or one and three depending on the vertex causing
concavity.
Vertices Outside
of a Begin/End Pair |
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HP's implementation of this specification is indeterminate
as defined by the OpenGL standard.
Index Mode Dithering |
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If dithering is enabled in indexed visuals, 2D functions such
as glDrawPixels
and glBitmap
will not be dithered.
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