RTC_GEOMETRY_TYPE_QUAD - Online Linux Manual Page

Section : 3
Updated :
Source :
Note : Embree Ray Tracing Kernels 3

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

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