tjames221188

04-20-2010, 09:40 AM

Hi there,

I don't usually like to ask for help but this has had me stumped for days!

I have been asked to produce a basic skeletal animation program for a uni project. The skeleton is very basic and uses gluCylinders to represent a bone. the quaternion class has been taken from the nehe quaternion camera class here (http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=Quaternion_Camera_Class). Most of it is done, however there is one problem that i cannot make any sense out of. I'm hoping that somebody has experienced a similar problem.

The problem:

Whenever I rotate a joint that has at least 1 child, the cylinder and all child cylinders grow and shrink as they rotate. it looks like this:

http://yfrog.com/50piczsj

here is the code for the structs:

//joints

struct arc {

glQuaternion q_vrot;//variable rotation

float matrix[16];//translates arc to correct position

Node *node;//child node

};

//bones

struct Node {

float length;//bone length

float matrix[16];//point of rotation

int num_arcs;//number of children

arc *arcs[4];//children

};

and here is the code for the methods that do the drawing:

GLvoid drawCylinder(GLfloat length)

{

glPushMatrix();

gluCylinder(quadratic, boneRadius, boneRadius, length, 32, 32);

gluDisk(quadratic, 0.0f, boneRadius*2.0f, 32, 32);

gluSphere(quadratic, boneRadius*1.5f, 32, 32);

glTranslatef(0.0f, 0.0f, length);

gluDisk(quadratic, 0.0f, boneRadius, 32, 32);

glPopMatrix();

}

GLvoid eval_node( GLfloat m[16], Node *node)

{

GLfloat temp_mat[16];//used to store the current matrix

GLfloat quat_mat[16];//used to store the matrix from the quaternion

//concatenate node matrix and current matrix

glMultMatrixf(node->matrix);

if (node->length > 0)

drawCylinder(node->length);

else

{

glPushMatrix();

gluSphere(quadratic, 0.5f, 32, 32);//if length !> 0 it must be the head, so draw a sphere

glPopMatrix();

}

/*loop over each arc coming from this node and follow

the arcs to recursively evaluate child nodes*/

for(int i = 0; i < node->num_arcs; i++)

{

glPushMatrix();

node->arcs[i]->q_vrot.CreateMatrix(quat_mat);

glMultMatrixf(node->arcs[i]->matrix);

glMultMatrixf(quat_mat);

glGetFloatv(GL_MODELVIEW_MATRIX, temp_mat);

eval_node(temp_mat, node->arcs[i]->node);

glPopMatrix();

}

}

//main routine evaluates recursively from root

GLvoid eval_tree(arc *a)

{

eval_node( a->matrix, a->node );

}

int DrawGLScene(GLvoid)

{

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glLoadIdentity();

glTranslatef(-camera.xpos, -camera.ypos, -camera.zpos);

//animation

left_shoulder2left_upper_arm.q_vrot.CreateFromAxis Angle(0.0f, 1.0f, 1.0f, rot);

eval_tree(&arc_root);

if (rot >= 360.0f)

rot = 0.0f;

else

rot+= 0.2f;

return TRUE;

}

Any suggestions would be hugely appreciated.

Many thanks in advance,

Toby.

I don't usually like to ask for help but this has had me stumped for days!

I have been asked to produce a basic skeletal animation program for a uni project. The skeleton is very basic and uses gluCylinders to represent a bone. the quaternion class has been taken from the nehe quaternion camera class here (http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=Quaternion_Camera_Class). Most of it is done, however there is one problem that i cannot make any sense out of. I'm hoping that somebody has experienced a similar problem.

The problem:

Whenever I rotate a joint that has at least 1 child, the cylinder and all child cylinders grow and shrink as they rotate. it looks like this:

http://yfrog.com/50piczsj

here is the code for the structs:

//joints

struct arc {

glQuaternion q_vrot;//variable rotation

float matrix[16];//translates arc to correct position

Node *node;//child node

};

//bones

struct Node {

float length;//bone length

float matrix[16];//point of rotation

int num_arcs;//number of children

arc *arcs[4];//children

};

and here is the code for the methods that do the drawing:

GLvoid drawCylinder(GLfloat length)

{

glPushMatrix();

gluCylinder(quadratic, boneRadius, boneRadius, length, 32, 32);

gluDisk(quadratic, 0.0f, boneRadius*2.0f, 32, 32);

gluSphere(quadratic, boneRadius*1.5f, 32, 32);

glTranslatef(0.0f, 0.0f, length);

gluDisk(quadratic, 0.0f, boneRadius, 32, 32);

glPopMatrix();

}

GLvoid eval_node( GLfloat m[16], Node *node)

{

GLfloat temp_mat[16];//used to store the current matrix

GLfloat quat_mat[16];//used to store the matrix from the quaternion

//concatenate node matrix and current matrix

glMultMatrixf(node->matrix);

if (node->length > 0)

drawCylinder(node->length);

else

{

glPushMatrix();

gluSphere(quadratic, 0.5f, 32, 32);//if length !> 0 it must be the head, so draw a sphere

glPopMatrix();

}

/*loop over each arc coming from this node and follow

the arcs to recursively evaluate child nodes*/

for(int i = 0; i < node->num_arcs; i++)

{

glPushMatrix();

node->arcs[i]->q_vrot.CreateMatrix(quat_mat);

glMultMatrixf(node->arcs[i]->matrix);

glMultMatrixf(quat_mat);

glGetFloatv(GL_MODELVIEW_MATRIX, temp_mat);

eval_node(temp_mat, node->arcs[i]->node);

glPopMatrix();

}

}

//main routine evaluates recursively from root

GLvoid eval_tree(arc *a)

{

eval_node( a->matrix, a->node );

}

int DrawGLScene(GLvoid)

{

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glLoadIdentity();

glTranslatef(-camera.xpos, -camera.ypos, -camera.zpos);

//animation

left_shoulder2left_upper_arm.q_vrot.CreateFromAxis Angle(0.0f, 1.0f, 1.0f, rot);

eval_tree(&arc_root);

if (rot >= 360.0f)

rot = 0.0f;

else

rot+= 0.2f;

return TRUE;

}

Any suggestions would be hugely appreciated.

Many thanks in advance,

Toby.