relief clipping planes (siggraph asia 2008)
TRANSCRIPT
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Matthias Trapp, Jürgen DöllnerHasso-Plattner-Institute, University of Potsdam, Germany
Relief Clipping PlanesFor Real-Time Rendering
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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ResultsResults
Solid Mesh
Relief Clipping Plane
Input
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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MotivationMotivation
Relief Clipping Planes (RCP):• Create more sophisticated cut-away views• Enables non-regular cut-surfaces
Contributions:• New clip plane parameterization• Automatic cap-surface generation
Implementation Goals:• Interactive configuration• Use hardware acceleration
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Relief Clip-Plane ParameterizationRelief Clip-Plane Parameterization
• O Plane Origin• U, V Direction Vectors• S = (sx,sy,sz) Scaling Vector• OM Offsetmap
( )
Vector Scaling
TexturemapOffset
Normal Plane
VectorsDirection ,
Origin
,,,,,
3
3
3
RS
OM
VUN
RVU
RO
SOMVUORCP
∈
×=∈
∈
=
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Clipping EquationClipping Equation
( )( )
( )( )
( ) ( )
⋅
•−⋅
•−=
⋅•−−=
<⋅+•−•
=
yN
xN
N
zsample
sV
VOPs
U
UOPT
NNOPPP
otherwisefalse
sTOMfONNPtruePRCPclip
,
0,,
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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GLSL Fragment-Shader SourceGLSL Fragment-Shader Source
bool clipReliefPlane(in mat4 config, // configuration matrixin vec4 point, // position in eye-spacein sampler2D reliefSampler) // 2D relief texture
{ // calculate plane in eye space...vec3 O = (gl_ModelViewMatrix * vec4(config[0].xyz, 1.0)).xyz; vec3 A = normalize( gl_NormalMatrix * normalize(config[1].xyz) );vec3 B = normalize( gl_NormalMatrix * normalize(config[2].xyz) );vec3 N = cross(A, B);// project current fragment coordinate on planevec3 pV = point.xyz - dot(point.xyz - O, N) * N;// calculate clip texture coordinatesfloat s = dot(pV - O, A) / length(config[1].xyz);float t = dot(pV - O, B) / length(config[2].xyz);// fetch height... maybe zerofloat height = texture2D(reliefSampler, vec2(s,t) * config[3].st).x;// calculate reference plane float plane = dot(point.xyz, N) - dot(N, O) + (height * config[3].z );return (plane < 0.0 && bool(config[3].w)); // perform clipping }
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Multiple Clipping PlanesMultiple Clipping Planes
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Capping Openings – The Goal…Capping Openings – The Goal…
http://www.bmbikes.co.uk/photos/museumphotos/Broken 20R60-6 Crank.jpg
Assumption: Input Mesh is SOLID.
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Capping – The ProcessCapping – The Process
Goals:• Convey material / inner structure of the input solid• Enable assisted modeling of cap-surface appearance Solution: Polygonal Cap-Surface• Directly derived from relief-clipping plane• Rendering after the clipping pass
=+Clipped Mesh Cap-Surface Final Result
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Generating the Cap-SurfaceGenerating the Cap-Surface
A B
RCP Derived Surface Clipped Surface
Phase A:• Dynamic Mesh Refinement on GPU [Boubekeur05]• Perform displacement, shading, texturing,…Phase B:• Clip away “outside” parts of the cap-surface
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Decision ProblemDecision Problem
Which point P of the cap-surface is inside a solid S ?
Solution: Volumetric depth test
Needed: Additional data structure• Layered Depth Image (LDI) [Shade98]• Image-based representation of shape• Computed in pre-processing [Everitt01]
( )
∉∈
=SPOutside
SPInsideSPVDT ,
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Example of Layered Depth ImageExample of Layered Depth ImageDepth Layers LDI = (LDI0,…,LDI7)
3D LDI Texture Space [0,1]3
Non-Convex Polygonal Mesh S with d = 8
3D World Space IR3
s
t
x
y
Depth-Peeling
z
O O
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Volumetric Depth TestVolumetric Depth Test
r
t
Tr
(s,1,0)
(s,0,1)
Ray R
Inside
Outside
d0 d1 d2 d3
(s,0,0)
(Ts ,Tt ,0)(Ts ,Tt ,1)pT =0 pT =1 pT =0 pT =1
S
(s,1,1)
[Trapp08]
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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ConclusionsConclusions
Summary• Advanced clipping approach• Real-time rendering technique• Fully implemented on GPU
Drawbacks• Needs additional data structure• Needs high-tessellated cap-surface
Future Work• Generalized approach for clipping
:: :: :: Relief Clipping Planes For Real-Time Rendering :: Matthias Trapp :: ::
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Thank You ! - Questions ? Thank You ! - Questions ?
Contact:Matthias [email protected]
Jürgen Dö[email protected]
Computer Graphics Systems Grouphttp://www.hpi.uni-potsdam.de/doellner/