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.TH "RTC_GEOMETRY_TYPE_QUAD" "3" "" "" "Embree Ray Tracing Kernels 4"
.SS NAME
.IP
.EX
RTC_GEOMETRY_TYPE_QUAD \- quad geometry type
.EE
.SS SYNOPSIS
.IP
.EX
#include <embree4/rtcore.h>

RTCGeometry geometry =
  rtcNewGeometry(device, RTC_GEOMETRY_TYPE_QUAD);
.EE
.SS DESCRIPTION
Quad meshes are created by passing \f[CR]RTC_GEOMETRY_TYPE_QUAD\f[R] to
the \f[CR]rtcNewGeometry\f[R] function call.
The quad indices can be specified by setting an index buffer
(\f[CR]RTC_BUFFER_TYPE_INDEX\f[R] type) and the quad vertices by setting
a vertex buffer (\f[CR]RTC_BUFFER_TYPE_VERTEX\f[R] type).
See \f[CR]rtcSetGeometryBuffer\f[R] and
\f[CR]rtcSetSharedGeometryBuffer\f[R] for more details on how to set
buffers.
The index buffer contains an array of four 32\-bit indices per quad
(\f[CR]RTC_FORMAT_UINT4\f[R] format), and the number of primitives is
inferred from the size of that buffer.
The vertex buffer contains an array of single precision \f[CR]x\f[R],
\f[CR]y\f[R], \f[CR]z\f[R] floating point coordinates
(\f[CR]RTC_FORMAT_FLOAT3\f[R] format), and the number of vertices is
inferred from the size of that buffer.
The vertex buffer can be at most 16 GB large.
.PP
A quad is internally handled as a pair of two triangles
\f[CR]v0,v1,v3\f[R] and \f[CR]v2,v3,v1\f[R], with the
\f[CR]u\[aq]\f[R]/\f[CR]v\[aq]\f[R] coordinates of the second triangle
corrected by \f[CR]u = 1\-u\[aq]\f[R] and \f[CR]v = 1\-v\[aq]\f[R] to
produce a quad parametrization where \f[CR]u\f[R] and \f[CR]v\f[R] are
in the range 0 to 1.
Thus the parametrization of a quad uses the first vertex \f[CR]p0\f[R]
as base point, and the vector \f[CR]p1 \- p0\f[R] as
\f[CR]u\f[R]\-direction, and \f[CR]p3 \- p0\f[R] as v\-direction.
Thus vertex attributes \f[CR]t0,t1,t2,t3\f[R] can be bilinearly
interpolated over the quadrilateral the following way:
.IP
.EX
t_uv = (1\-v)((1\-u)*t0 + u*t1) + v*((1\-u)*t3 + u*t2)
.EE
.PP
Mixed triangle/quad meshes are supported by encoding a triangle as a
quad, which can be achieved by replicating the last triangle vertex
(\f[CR]v0,v1,v2\f[R] \-> \f[CR]v0,v1,v2,v2\f[R]).
This way the second triangle is a line (which can never get hit), and
the parametrization of the first triangle is compatible with the
standard triangle parametrization.
.PP
A quad whose vertices are laid out counter\-clockwise has its geometry
normal pointing upwards outside the front face, like illustrated in the
following picture.
.IP
.EX
.EE
.PP
For multi\-segment motion blur, the number of time steps must be first
specified using the \f[CR]rtcSetGeometryTimeStepCount\f[R] call.
Then a vertex buffer for each time step can be set using different
buffer slots, and all these buffers must have the same stride and size.
.SS EXIT STATUS
On failure \f[CR]NULL\f[R] is returned and an error code is set that can
be queried using \f[CR]rtcGetDeviceError\f[R].
.SS SEE ALSO
[rtcNewGeometry]