大三05计算机图形学modeling ii

1、Hierarchical Modeling II1Angel: Interactive Computer Graphics 5E Addison-Wesley 2009原著Ed AngelProfessor of Computer Science, Electrical and Computer Engineering, and Media ArtsUniversity of New Mexico编辑 武汉大学计算机学院图形学课程组2Angel: Interactive Computer Graphics 5E Addison-Wesley 2009ObjectivesBuild a tree

2、-structured model of a humanoid figureExamine various traversal strategiesBuild a generalized tree-model structure that is independent of the particular model3Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Humanoid Figure4Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Buildin

3、g the ModelCan build a simple implementation using quadrics: ellipsoids and cylindersAccess parts through functionstorso()left_upper_arm()Matrices describe position of node with respect to its parentMlla positions left lower leg with respect to left upper arm5Angel: Interactive Computer Graphics 5E

4、Addison-Wesley 2009Tree with Matrices6Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Display and TraversalThe position of the figure is determined by 11 joint angles (two for the head and one for each other part)Display of the tree requires a graph traversalVisit each node onceDisplay fu

5、nction at each node that describes the part associated with the node, applying the correct transformation matrix for position and orientation7Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Transformation MatricesThere are 10 relevant matricesM positions and orients entire figure through

6、the torso which is the root nodeMh positions head with respect to torsoMlua, Mrua, Mlul, Mrul position arms and legs with respect to torsoMlla, Mrla, Mlll, Mrll position lower parts of limbs with respect to corresponding upper limbs8Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Stack-ba

7、sed TraversalSet model-view matrix to M and draw torsoSet model-view matrix to MMh and draw headFor left-upper arm need MMlua and so onRather than puting MMlua from scratch or using an inverse matrix, we can use the matrix stack to store M and other matrices as we traverse the tree9Angel: Interactiv

8、e Computer Graphics 5E Addison-Wesley 2009Traversal Codefigure() glPushMatrix() torso(); glRotate3f(); head(); glPopMatrix(); glPushMatrix(); glTranslate3f(); glRotate3f(); left_upper_arm(); glPopMatrix(); glPushMatrix();save present model-view matrixupdate model-view matrix for headrecover original

9、 model-view matrixsave it againupdate model-view matrix for left upper armrecover and save original model-view matrix againrest of code10Angel: Interactive Computer Graphics 5E Addison-Wesley 2009AnalysisThe code describes a particular tree and a particular traversal strategyCan we develop a more ge

10、neral approach?Note that the sample code does not include state changes, such as changes to colorsMay also want to use glPushAttrib and glPopAttrib to protect against unexpected state changes affecting later parts of the code11Angel: Interactive Computer Graphics 5E Addison-Wesley 2009General Tree D

11、ata StructureNeed a data structure to represent tree and an algorithm to traverse the treeWe will use a left-child right sibling structureUses linked listsEach node in data structure is two pointersLeft: next nodeRight: linked list of children12Angel: Interactive Computer Graphics 5E Addison-Wesley

12、2009Left-Child Right-Sibling Tree13Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Tree node StructureAt each node we need to store Pointer to siblingPointer to childPointer to a function that draws the object represented by the nodeHomogeneous coordinate matrix to multiply on the right o

13、f the current model-view matrixRepresents changes going from parent to nodeIn OpenGL this matrix is a 1D array storing matrix by columns 14Angel: Interactive Computer Graphics 5E Addison-Wesley 2009C Definition of treenodetypedef struct treenode GLfloat m16; void (*f)(); struct treenode *sibling; st

14、ruct treenode *child; treenode;15Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Defining the torso nodetreenode torso_node, head_node, lua_node, ; /* use OpenGL functions to form matrix */glLoadIdentity();glRotatef(theta0, 0.0, 1.0, 0.0); /* move model-view matrix to m */glGetFloatv(GL_M

15、ODELVIEW_MATRIX, torso_node.m)torso_node.f = torso; /* torso() draws torso */Torso_node.sibling = NULL;Torso_node.child = &head_node; 16Angel: Interactive Computer Graphics 5E Addison-Wesley 2009NotesThe position of figure is determined by 11 joint angles stored in theta11Animate by changing the ang

16、les and redisplayingWe form the required matrices using glRotate and glTranslate More efficient than softwareBecause the matrix is formed in model-view matrix, we may want to first push original model-view matrix on matrix stack17Angel: Interactive Computer Graphics 5E Addison-Wesley 2009Preorder Tr

17、aversalvoid traverse(treenode *root) if(root = NULL) return; glPushMatrix(); glMultMatrix(root-m); root-f(); if(root-child != NULL) traverse(root-child); glPopMatrix(); if(root-sibling != NULL) traverse(root-sibling);18Angel: Interactive Computer Graphics 5E Addison-Wesley 2009NotesWe must save mode

18、l-view matrix before multiplying it by node matrix Updated matrix applies to children of node but not to siblings which contain their own matricesThe traversal program applies to any left-child right-sibling treeThe particular tree is encoded in the definition of the individual nodesThe order of traversal matters because of possible state changes in the functions19Angel: Interactive Computer Gr