Manpages - RTC_GEOMETRY_TYPE_QUAD.3embree3
Table of Contents
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NAME
RTC_GEOMETRY_TYPE_QUAD - quad geometry type
SYNOPSIS
#include <embree3/rtcore.h> RTCGeometry geometry = rtcNewGeometry(device, RTC_GEOMETRY_TYPE_QUAD);
DESCRIPTION
Quad meshes are created by passing RTC_GEOMETRY_TYPE_QUAD
to the
rtcNewGeometry
function call. The quad indices can be specified by
setting an index buffer (RTC_BUFFER_TYPE_INDEX
type) and the quad
vertices by setting a vertex buffer (RTC_BUFFER_TYPE_VERTEX
type). See
rtcSetGeometryBuffer
and rtcSetSharedGeometryBuffer
for more details
on how to set buffers. The index buffer contains an array of four 32-bit
indices per quad (RTC_FORMAT_UINT4
format), and the number of
primitives is inferred from the size of that buffer. The vertex buffer
contains an array of single precision x
, y
, z
floating point
coordinates (RTC_FORMAT_FLOAT3
format), and the number of vertices is
inferred from the size of that buffer. The vertex buffer can be at most
16 GB large.
A quad is internally handled as a pair of two triangles v0,v1,v3
and
v2,v3,v1
, with the u'=/=v'
coordinates of the second triangle
corrected by u = 1-u'
and v = 1-v'
to produce a quad parametrization
where u
and v
are in the range 0 to 1. Thus the parametrization of a
quad uses the first vertex p0
as base point, and the vector p1 - p0
as u
-direction, and p3 - p0
as v-direction. Thus vertex attributes
t0,t1,t2,t3
can be bilinearly interpolated over the quadrilateral the
following way:
t_uv = (1-v)((1-u)*t0 + u*t1) + v*((1-u)*t3 + u*t2)
Mixed triangle/quad meshes are supported by encoding a triangle as a
quad, which can be achieved by replicating the last triangle vertex
(v0,v1,v2
-> v0,v1,v2,v2
). 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.
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.
For multi-segment motion blur, the number of time steps must be first
specified using the rtcSetGeometryTimeStepCount
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.
EXIT STATUS
On failure NULL
is returned and an error code is set that can be
queried using rtcGetDeviceError
.
SEE ALSO
[rtcNewGeometry]