CN105488843A - Point cloud based method for calculating emergent irradiance of sub-surface scattering object - Google Patents
Point cloud based method for calculating emergent irradiance of sub-surface scattering object Download PDFInfo
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Abstract
The invention discloses a point cloud based method for calculating emergent irradiance of a sub-surface scattering object. The method comprises the steps of (1): sampling the surface of the sub-surface scattering object, then performing direct illumination calculation on a sampling point on the surface of the sub-surface scattering object to form a point cloud sampling point, and organizing the point cloud sampling point into a point cloud tree for storage; and (2): performing a light ray tracing and rendering process for rendering, wherein a cross point of each light ray and a scene containing a plurality of three-dimensional objects is a coloring point; when the coloring point falls on the sub-surface scattering object, traversing the point cloud tree to obtain a tree cut associated with the emergent irradiance of the current coloring point, performing integration on the incident irradiance of the current coloring point by each node on the tree cut, and performing calculation according to a sub-surface scattering function to obtain the emergent irradiance of the current coloring point in any direction.
Description
Technical field
The present invention relates to Subsurface Scattering Realistic Rendering, be specifically related to a kind of outgoing irradiance computing method of the Subsurface Scattering object based on a cloud.
Background technology
Subsurface Scattering (subsurfacescattering) refers to that light enters object from body surface point, through scattering-in, finally from the light transmittance process of other summit outgoing of body surface.The object with Subsurface Scattering character generally has comparatively mellow and full appearance luster, and this phenomenon shows more obvious in translucent material, and the milk in real world, jade, marble and biological epidermis etc. all have this character.Subsurface Scattering generally needs to adopt Bidirectional surface scattered reflection distribution function (bidirectionalsurfacescatteringreflectancedistributionfun ction, be called for short BSSRDF) be described, and adopt global illumination algorithm to draw.Therefore being modeled in order to one, Realistic Rendering field is extremely important and have challenging problem Subsurface Scattering material.
But simulation has the object not a duck soup of Subsurface Scattering characteristic, light is in the inside injecting translucent object, and then through repeatedly rebounding, penetrate body surface again through scattering with after absorbing, this process is very complicated.Use the such as monte carlo method such as path tracing (pathtracing) and Photon Mapping (photonmapping) that very accurate Subsurface Scattering result can be obtained, but needs expend the extremely long time just can reach convergence.Current widely used method has Subsurface Scattering method based on precomputation and Subsurface Scattering Approximate Simulation Method two type.
Such as, within 2002, Jensen proposes the radiometric algorithm of precomputation in " Arapidhierarchicalrenderingtechniquefortranslucentmateri als " literary composition, adopt layering integral way, use the irradiance of precalculated sampled point to calculate Depth experiment to simulate Subsurface Scattering, the playing up of object with highly transparent characteristic is seemed particularly efficient.
A kind of real-time global illumination method of the Subsurface Scattering object based on radiometric algorithms is proposed in Chinese patent (application number: CN201210293255, patent name: the real-time global illumination method based on the Subsurface Scattering object of radiometric algorithms).Gone out the Energy Transfer matrix of scene by radiometric algorithms's precomputation, and utilize the rapid sparse matrix storehouse of GPU to calculate energy transport, finally utilize fast photon collection algorithm, obtain final global illumination effect.This patent solves the global illumination effect of the Subsurface Scattering object under any light source illumination, and can reach real-time in speed.
Chinese patent (application number: CN201110281048, patent name: a kind of real-time drawing method of the Subsurface Scattering based on BRDF) to Subsurface Scattering model refinement, the method of employing BRDF carrys out the single Subsurface Scattering in close approximation Subsurface Scattering, by the abbreviation to integration, simplify a large amount of calculated amount that traditional illumination model brings to improve drafting efficiency.
Subsurface Scattering method based on precomputation can realize high-quality Subsurface Scattering effect, but pre-service cost is high, and needs efficient storage organization to store pre-processed results, to accelerate in illumination calculation process; Subsurface Scattering Approximate Simulation Method, is not the method for physically based deformation, rendering quality is lost.
Summary of the invention
The present invention is directed to irradiance pre-calculation process cost height and storage challenge in the Subsurface Scattering method based on precomputation, a kind of outgoing irradiance computing method of the Subsurface Scattering object based on a cloud are provided.The method is by the surface sampling also direct irradiation generation point cloud to Subsurface Scattering object, point cloud tree is adopted to store a cloud, in render process, for arbitrary colored spots by searching some cloud tree and the Integral Technology of precomputation, quick calculating, with the Subsurface Scattering of surfaceness, finally obtains the outgoing irradiance of Subsurface Scattering object.
For achieving the above object, the present invention is by the following technical solutions:
Based on outgoing irradiance computing method for the Subsurface Scattering object of a cloud, comprising:
Step (1): Subsurface Scattering body surface is sampled, more direct illumination calculation is carried out to the sampled point on Subsurface Scattering body surface form Points Sample point, and Points Sample point is organized into a Yun Shuzhong stores;
Step (2): unlatching ray tracing is played up flow process and played up, the point that every bar light and the scene comprising multiple three-dimensional body intersect is colored spots; When colored spots drops on Subsurface Scattering object, obtain by traversal point cloud tree the tree be associated with the outgoing irradiance of current coloration point to cut, the incident irradiance degree of each node cut by described tree to current coloration point all carries out integration, calculates the irradiance of current coloration point along either direction outgoing according to Subsurface Scattering function.
In described step (1), REYES algorithm is adopted to carry out interpolation sampling at Subsurface Scattering body surface.
Adopt REYES algorithm that the surface of Subsurface Scattering object is divided into several polygons, described polygonal center of gravity is as the position of Points Sample point.
By calculating the polygonal area at each Points Sample point place, obtain the area of respective point cloud sampled point representative.
In described step (1), some cloud tree is K-D tree construction.
In described step (1), adopt binary tree structure memory point cloud tree.
In described step (1), the leaf node memory point cloud sampled point of some cloud tree, the nonleaf node of some cloud tree stores the solar global irradiance of its all child nodes, and the total area of all child nodes representatives, through the mean place of all child nodes positions of irradiance weighting.
In step (2), traversal point cloud tree from the root node of Dian Yunshu, at each Nodes of Dian Yunshu, if this node meets following arbitrary condition:
A the area of () this node on behalf and current coloration point are less than predetermined threshold value to the ratio of the distance of this node location;
B () this node is leaf node;
Then this node is associated with the outgoing irradiance of current coloration point, stops the child node of this node of traversal; Otherwise, travel through all child nodes of this node, and judge whether all child nodes of this node meet above-mentioned arbitrary condition, until find all nodes meeting above-mentioned arbitrary condition, these nodes form the tree be associated with the outgoing irradiance of current coloration point and cut.
In step (2), after the incident irradiance degree of each node that described tree cuts to current coloration point carries out integration, then superpose high light item, finally draw the irradiance of current coloration point along either direction outgoing; Wherein, the high light item accumulated value that is each node of being cut by described tree to the product term of the incident irradiance degree of current coloration point and corresponding high backscatter extinction logarithmic ratio.
Beneficial effect of the present invention is:
(1) the present invention is by the tree structure of level traversal memory point cloud, thus reaches the object of Fast rendering, can simulate the Subsurface Scattering effects such as smooth jade;
(2) the effective tissue of the present invention by setting a cloud, can find colored spots contributive some cloud tree node fast, while quality is played up in guarantee, sampled point on the impact of current coloration point exponentially function decline and improve the efficiency of the method for this layered method.
Accompanying drawing explanation
Fig. 1 is the process flow diagram of the outgoing irradiance computing method of the Subsurface Scattering object based on a cloud of the present invention.
Embodiment
Below in conjunction with accompanying drawing and embodiment, the present invention will be further described:
Fig. 1 is the process flow diagram of the outgoing irradiance computing method of the Subsurface Scattering object based on a cloud of the present invention, and according to this figure, can find out, the method for the present invention, comprising: pre-treatment step and rendering step.
(1) pre-treatment step
Subsurface Scattering body surface is sampled, more direct illumination is carried out to the sampled point on Subsurface Scattering body surface forms Points Sample point, and Points Sample point is organized into a Yun Shuzhong stores.
In this step, REYES algorithm is adopted to carry out interpolation sampling at Subsurface Scattering body surface.Point cloud tree adopts K-D tree construction.
The present embodiment adopts binary tree structure memory point cloud tree.
In this step, the leaf node of some cloud tree is Points Sample point, non-leaf nodes store its child nodes and, the node of any point cloud tree stores the position of this node, area and irradiance.
Adopt REYES algorithm that the surface of Subsurface Scattering object is divided into several polygons, described polygonal center of gravity is as Points Sample point.
By calculating the polygonal area at each Points Sample point place, obtain the area of respective point cloud sampled point representative.
Such as: adopt REYES algorithm, close by face and hidden surface blanking, Subsurface Scattering body surface is subdivided into micro-polygon (micropolygons).Micro-polygon, for quadrilateral, calculates the Points Sample point that the center of gravity of micropolygon goes out as interpolation.
Each Points Sample point calculates the area of its representative, i.e. the area of the micropolygons at its place, computing method for by micropolygons quadrilateral being divided into two triangles, two triangle areas and the exact area that is micropolygon.
Calculate the irradiance information of direct illumination as this point of each Points Sample point.
In the present embodiment, adopt K-D tree to be organized in a hierarchical structure by a cloud, the present invention adopts binary tree structure memory point cloud to set.Wherein, a some cloud is stored in leaf node; Each attribute that intermediate node stores be to its each attribute of child nodes add and, i.e. total irradiance of all child nodes, the total area of all child nodes representative, through the mean place of all child nodes positions of irradiance weighting.
(2) rendering step
Unlatching ray tracing is played up flow process and is played up, and the point that every bar light and the scene comprising multiple three-dimensional body intersect is colored spots; When colored spots drops on Subsurface Scattering object, obtain by traversal point cloud tree the tree be associated with the outgoing irradiance of current coloration point to cut, the incident irradiance degree of each node cut by described tree to current coloration point all carries out integration, calculates the irradiance of current coloration point along either direction outgoing according to Subsurface Scattering function.
In this step, traversal point cloud tree from the root node of Dian Yunshu, at each Nodes of Dian Yunshu, if this node meets following arbitrary condition:
A the area of () this node on behalf and current coloration point are less than predetermined threshold value to the ratio of the distance of this node location;
B () this node is leaf node;
Then this node is associated with the outgoing irradiance of current coloration point, stops the child node of this node of traversal; Otherwise, travel through all child nodes of this node, and judge whether all child nodes of this node meet above-mentioned arbitrary condition, until find all nodes meeting above-mentioned arbitrary condition, obtain the tree be associated with the outgoing irradiance of current coloration point and cut.
The incident irradiance degree of each node cut by described tree to current coloration point all carries out integration, can also be added with high optical oomputing item.Use blinn illumination model when calculating high light, high backscatter extinction logarithmic ratio is by formula (RV)
αcalculate, wherein R represents the reflection vector at this colored spots place, and V represents the vector of color dot to viewpoint direction, and α is rough object surfaces degree, the product of high backscatter extinction logarithmic ratio and incident irradiance degree is the value of Gao Guang, and final adding up draws the irradiance of current coloration point along either direction outgoing.
A expression formula that the area of () this node on behalf and current coloration point are less than predetermined threshold value to the ratio of the distance of this node location is:
Wherein, A
vfor the area of node,
for the position of colored spots,
for node location.
By judging whether Δ ω is less than certain constant, determine to travel through the need of to the child nodes of node.
In this step, the computing formula of integration is carried out according to the incident irradiance degree of Subsurface Scattering function to each node that described tree cuts as follows:
Wherein,
at colored spots x
owith angle ω
oemergent light,
that tree cuts each node incidence point from direction
incident light, S is BSSRDF function;
for the colored spots x on subsurface body surface
inormal vector.
S is that the formula of BSSRDF function is as follows:
Wherein, variable
with
the Fresnel reflection rate at incidence point and eye point place respectively; R
d(|| x
i-x
o||) be diffuse reflectance for approximate Subsurface Scattering, represent from colored spots x
ithe light injecting interior of articles through scattering and absorption, then from the colored spots x of body surface
oinjection, the luminous energy of this wherein outgoing accounts for the ratio initially injecting luminous energy, and the scattering of material and absorption parameter all can affect the result of this function; η represents refractive index.
By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.
Claims (9)
1., based on outgoing irradiance computing method for the Subsurface Scattering object of a cloud, it is characterized in that, comprising:
Step (1): Subsurface Scattering body surface is sampled, more direct illumination calculation is carried out to the sampled point on Subsurface Scattering body surface form Points Sample point, and Points Sample point is organized into a Yun Shuzhong stores;
Step (2): unlatching ray tracing is played up flow process and played up, the point that every bar light and the scene comprising multiple three-dimensional body intersect is colored spots; When colored spots drops on Subsurface Scattering object, obtain by traversal point cloud tree the tree be associated with the outgoing irradiance of current coloration point to cut, the incident irradiance degree of each node cut by described tree to current coloration point all carries out integration, calculates the irradiance of current coloration point along either direction outgoing according to Subsurface Scattering function.
2. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 1, is characterized in that, in described step (1), adopt REYES algorithm to carry out interpolation sampling at Subsurface Scattering body surface.
3. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 2, it is characterized in that, adopt REYES algorithm that the surface of Subsurface Scattering object is divided into several polygons, described polygonal center of gravity is as the position of Points Sample point.
4. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 3, is characterized in that, by calculating the polygonal area at each Points Sample point place, obtain the area of respective point cloud sampled point representative.
5. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 1, is characterized in that, in described step (1), some cloud tree is K-D tree construction.
6. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 5, is characterized in that, in described step (1), adopt binary tree structure memory point cloud tree.
7. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 4, it is characterized in that, in described step (1), the leaf node memory point cloud sampled point of some cloud tree, the nonleaf node of some cloud tree stores the solar global irradiance of its all child nodes, the total area of all child nodes representatives, through the mean place of all child nodes positions of irradiance weighting.
8. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 1, it is characterized in that, in step (2), traversal point cloud tree from the root node of Dian Yunshu, at each Nodes of Dian Yunshu, if this node meets following arbitrary condition:
A the area of () this node on behalf and current coloration point are less than predetermined threshold value to the ratio of the distance of this node location;
B () this node is leaf node;
Then this node is associated with the outgoing irradiance of current coloration point, stops the child node of this node of traversal; Otherwise, travel through all child nodes of this node, and judge whether all child nodes of this node meet above-mentioned arbitrary condition, until find all nodes meeting above-mentioned arbitrary condition, obtain the tree be associated with the outgoing irradiance of current coloration point and cut.
9. the outgoing irradiance computing method of a kind of Subsurface Scattering object based on a cloud as claimed in claim 1, it is characterized in that, in step (2), after the incident irradiance degree of each node that described tree cuts to current coloration point carries out integration, superpose high light item again, finally draw the irradiance of current coloration point along either direction outgoing; Wherein, the high light item accumulated value that is each node of being cut by described tree to the product term of the incident irradiance degree of current coloration point and corresponding high backscatter extinction logarithmic ratio.
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