Computer graphics MN1

Size: px

Start display at page:

Download "Computer graphics MN1"

Anissa Shepherd
6 years ago
Views:

1 Computer graphics MN1 Hierarchical modeling Transformations in OpenGL glmatrixmode(gl_modelview); glloadidentity(); // identity matrix gltranslatef(4.0, 5.0, 6.0); glrotatef(45.0, 1.0, 2.0, 3.0); gltranslatef(-4.0, -5.0, -6.0); C=T(4.0,5.0,6.0) R(45,1.0,2.0,3.0) T(-4.0,-5.0,-6.0) q=cp The transformation specified last is the one applied first OpenGL matrix stacks The matrix stacks can be used for implementing hierarchical transforms A copy of the current matrix is pushed onto the stack by using glpushmatrix() It is fetched again by using glpopmatrix() The current matrix is the one on top of the stack 32 4x4 matrices (GL_MODELVIEW) OpenGL matrix stacks OpenGL matrix stacks glpushmatrix() duplicates the current matrix Remember where you are OpenGL matrix stacks glpopmatrix() deletes the current matrix Go back to where you were 1

$Example void initglut( int &argc, char **argv) { glutinit( &argc,argv ); // Get two frame buffers with GLUT_DOUBLE glutinitdisplaymode( GLUT_DOUBLE GLUT_RGB GLUT_DEPTH ); glutinitwindowsize( 512, 512$

2 Example void initglut( int &argc, char **argv) { glutinit( &argc,argv ); // Get two frame buffers with GLUT_DOUBLE glutinitdisplaymode( GLUT_DOUBLE GLUT_RGB GLUT_DEPTH ); glutinitwindowsize( 512, 512 ); glutinitwindowposition( 100, 100 ); glutcreatewindow( TITLE ); void initgl() { glclearcolor( 0.0, 0.0, 0.0, 0.0 ); glmatrixmode( GL_PROJECTION ); glloadidentity(); gluperspective(65.0, 1.0, 1.0, 20.0 ); glmatrixmode (GL_MODELVIEW ); glloadidentity(); glulookat(1,-4,-4,0,0,0,0,1,0); glenable(gl_depth_test); glshademodel( GL_SMOOTH ); void polygon(int a, int b, int c, int d) { glbegin(gl_polygon); glcolor3fv(colors[a]); glnormal3fv(normals[a]); glvertex3fv(vertices[a]);... glend(); void draw() { glclear(gl_color_buffer_bit GL_DEPTH_BUFFER_BIT); void colorcube(void) { // Draw the different sides. polygon(0,3,2,1); polygon(2,3,7,6); polygon(0,4,7,3); polygon(1,2,6,5); polygon(4,5,6,7); polygon(0,1,5,4); // push the current transform matrix glrotatef(theta[0],1,0,0); glrotatef(theta[1],0,1,0); glrotatef(theta[2],0,0,1); colorcube(); // draw the cube // pop the matrix from the stack // push the matrix onto the stack gltranslatef(2,1,0); glrotatef(45,1,0,1); glscalef(0.2,0.5,0.5); colorcube(); // draw the small block // pop the matrix from the stack glflush(); glutswapbuffers(); 2

$0; glutpostredisplay(); void mouse(int btn, int state, int x, int y) { if(btn==glut_left_button && state==glut_down) axis = 0; if(btn==glut_middle_button && state==glut_down) axis = 1;$

3 void animate() { theta[axis] +=2.0; if(theta[axis]>360.0) theta[axis]-=360.0; glutpostredisplay(); void mouse(int btn, int state, int x, int y) { if(btn==glut_left_button && state==glut_down) axis = 0; if(btn==glut_middle_button && state==glut_down) axis = 1; if(btn==glut_right_button && state==glut_down) axis = 2; int main(int argc, char **argv) { initglut(argc, argv); initgl(); // Set the callback functions. glutdisplayfunc( draw ); glutidlefunc( animate ); glutmousefunc( mouse ); //Start the GLUT main Loop. glutmainloop(); return 0; Symbols and instances A collection of simple objects such as spheres, cubes,, cylinders, Compose complex objects from these primitives Regard primitives as symbols and each realization as an instance Location, orientation,, and size: instance transform Symbols and instances A table data structure allows us to transform objects and to add/delete objects Hierarchical modeling Hierarchical modeling A table is not a hierarchical data structure Want a structure that shows relationships among the components Consider a model of a car: The weels are identical except from position and orientation We would like to couple wheel motion and chassis motion, not use separate translations 3

Drawing arms with glutsolidcube() M=TRS Drawing base with

4 Hirarchical modeling A tree data structure for the car model shows the relationship between components A robot Three coordinate systems Drawing arms with glutsolidcube() M=TRS Drawing base with glucylinder() Transforms M=TRS uah Translatef(0,bh+lah,0); lah Translatef(0,bh,0); bh 4

5 Transforms Ry(θ) T(bh) Rz(α) T(lah) Rz(β) Ry(θ) T(bh) Rz(α) Ry(θ) #ifdef WIN32 #include <windows.h> #endif #include <cstdlib> #include <GL/glut.h> using namespace std; #define BASE_HEIGHT 4.0 #define BASE_RADIUS 2.0 #define LOWER_ARM_HEIGHT 4.0 #define LOWER_ARM_WIDTH 1.0 #define UPPER_ARM_HEIGHT 4.0 #define UPPER_ARM_WIDTH 1.0 void base() { glcolor3f(.7,0.0,0.0); // cylinder aligned with z axis as default // rotate cylinder to align with y axis glrotatef(-90.0, 1.0, 0.0, 0.0); glucylinder(p, BASE_RADIUS, BASE_RADIUS, BASE_HEIGHT, 20, 5); void upper_arm() { glcolor3f(0.0,.7,0.0); gltranslatef(0.0, 0.5*UPPER_ARM_HEIGHT, 0.0); glscalef(upper_arm_width, UPPER_ARM_HEIGHT, UPPER_ARM_WIDTH); glutsolidcube(1.0); void lower_arm() { glcolor3f(0.0,0.0,.7); gltranslatef(0.0, 0.5*LOWER_ARM_HEIGHT, 0.0); glscalef(lower_arm_width, LOWER_ARM_HEIGHT, LOWER_ARM_WIDTH); glutsolidcube(1.0); void display(void) { glclear(gl_color_buffer_bit GL_DEPTH_BUFFER_BIT); glloadidentity(); // this rotation applies to all three parts of the robot glrotatef(theta[0], 0.0, 1.0, 0.0); base(); // this only applies to the upper and lower arm gltranslatef(0.0, BASE_HEIGHT, 0.0); glrotatef(theta[1], 0.0, 0.0, 1.0); lower_arm(); // this only applies to the upper arm gltranslatef(0.0, LOWER_ARM_HEIGHT, 0.0); glrotatef(theta[2], 0.0, 0.0, 1.0); upper_arm(); glflush(); glutswapbuffers(); 5

$void mouse(int btn, int state, int x, int y) { // left button increase joint angle, // right button decreases it if(btn==glut_left_button && state == GLUT_DOWN){ theta[axis] += 5.$

6 void mouse(int btn, int state, int x, int y) { // left button increase joint angle, // right button decreases it if(btn==glut_left_button && state == GLUT_DOWN){ theta[axis] += 5.0; if( theta[axis] > ) theta[axis] -= 360.0; if(btn==glut_right_button && state == GLUT_DOWN){ theta[axis] -= 5.0; if( theta[axis] < ) theta[axis] += 360.0; display(); // menu callback void menu(int id) { // menu selects which angle to change or whether to // quit if(id == 1 ) axis=0; if(id == 2 ) axis=1; if(id == 3 ) axis=2; if(id == 4 ) exit(0); Result int main(int argc, char **argv) { glutinit(&argc, argv); glutinitdisplaymode(glut_double GLUT_RGB GLUT_DEPTH); glutinitwindowsize(500, 500); glutcreatewindow("robot"); // initialize (lights) myinit(); // menu glutaddmenuentry("base", 1); glutaddmenuentry("lower arm", 2); glutaddmenuentry("upper arm", 3); glutaddmenuentry("quit", 4); glutattachmenu( GLUT_MIDDLE_BUTTON); // start the loop glutmainloop(); return 0; Tree data structures Tree data structures A tree is a type of graph that consists of nodes and edges All nodes except the root node have a parent node and a number of child nodes A node without children is called a leaf node If we store necessary information in the nodes we need at least three components A (pointer to) function that draws the object A matrix that transforms the node and its children relative to its parent Pointers to children We can also store information about, e.g.,., color and material properties 6

Tree traversal To draw the whole object we need to visit all nodes, compute the correct matrix, and display the primitives Tree data structures A recursive pre-order traversal can be implemented

implemented in a natural way by using object-oriented oriented programming We can define a base-class node and derive other classes by inheritance Object-oriented modeling class node { node();

7 Tree traversal To draw the whole object we need to visit all nodes, compute the correct matrix, and display the primitives Tree data structures A recursive pre-order traversal can be implemented using OpenGL s matrix stack Tree data structures We do not want to create a new function for each model The data structure should be model independent Object-oriented modeling A tree structure can be implemented in a natural way by using object-oriented oriented programming We can define a base-class node and derive other classes by inheritance Object-oriented modeling class node { node(); virtual ~node(); virtual void render(); void addchild(node *n); node *children; ; class geometry : public node { geometry(); ~geometry(); virtual void render(); void setcolor(color c); void setmaterial(material m); ; class sphere : public geometry { float radius; sphere(float r=1.0); void render(); ; class transform : public node { matrix M; transform(matrix m); void render(); ; Scene graphs A general data structure to represent a whole scene We can have nodes for geometrical objects,, transforms, cameras, lights,, Each node can contain attributes such as color,, material, render mode, Here we can use OpenGL s attribute stack ( glpushattrib(), glpopattrib() ) 7

Scene graphs Simple scene graph API in the textbook (Angel) which can be downloaded from the web OpenInventor is a object-oriented oriented scene graph based toolkit built on top of OpenGL http://oss.

8 Scene graphs Simple scene graph API in the textbook (Angel) which can be downloaded from the web OpenInventor is a object-oriented oriented scene graph based toolkit built on top of OpenGL oss.sgi.com/projects/inventor/ VRML (X3D) is a general scene graph language used to facilitate 3D graphics on the web Assignment 4 Assignment 4 In the previous assignments you wrote your own algorithms, now it's time to get some feeling for a widely used API. In this assignment you should: Implement hierarchical transforms with animation in an OpenGL environment. Increase realism with the help of texture mapping,, material properties,, and lighting. Implement a simple mouse interface. Be creative! Assignment 4 On the course webpage there is a small C++ code package that you can use.. It is not a scene graph package. OpenGL functions are wrapped in C++ classes Ex.: Lightsource,, Camera, Geometry,, The code package is not complete in any sense. You are encouraged to extend it with your ideas. If you rather write your own code, feel free to do that. Lightsource.hh (sample) class Lightsource { protected: GLenum gl_light; Color ambient; Color diffuse; Color specular; Vector3h position; Vector3 direction; float exponent; float cutoff; float constant_attenuation; float linear_attenuation; float quadratic_attenuation; void setambient(const Color &col) { ambient = col; gllightfv(gl_light, GL_AMBIENT, ambient.data); Geometry.hh (sample) class Geometry { protected: Material material; unsigned int texture; Geometry() : texture(0) { virtual ~Geometry() { virtual void setmaterial(const Material &mat) { material = mat; virtual void settexture(unsigned int tex) { texture = tex; // This function does the real rendering, // i.e., vertices, normals, and polygons. // Should be implemented in derived classes virtual void makegl() = 0; 8

9 Geometry.hh (sample) // here we set the material properties and bind the texture virtual void render() { // push attributes on the attribute stack glpushattrib(gl_all_attrib_bits); // bind the texture glbindtexture(gl_texture_2d, this->texture); // set material properties glmaterialfv(gl_front_and_back, GL_AMBIENT, this->material.ambient.data); glmaterialfv(gl_front_and_back, GL_DIFFUSE, this->material.diffuse.data); // the actual rendering makegl(); // pop attributes glpopattrib(); Plane.hh (sample) // a plane, drawn in the xy plane class Plane : public Geometry { Plane(float _width, float _height) : width(_width), height(_height) { virtual ~Plane() { virtual void makegl() { glscalef(width,height,1); glbegin(gl_quads); gltexcoord2f(0,0); glnormal3f(0,0,1); glvertex3f(-.5,.5, 0.0); gltexcoord2f(1,0); glnormal3f(0,0,1); glvertex3f(.5,.5, 0.0); gltexcoord2f(1,1); glnormal3f(0,0,1); glvertex3f(.5,-.5, 0.0); gltexcoord2f(0,1); glnormal3f(0,0,1); glvertex3f(-.5,-.5, 0.0); glend(); planets.cpp (sample) // lights (in init function) light1 = new Lightsource(GL_LIGHT1); light1 -> setposition(vector3h(-500.0, 500.0, 500.0, 1.0)); // space (in init function) space = new Plane(500, 250); space -> settexture(loadgltextures("textures/stars.bmp")); // draw space (in display function) gltranslatef(0,0,-400); space->render(); 9

Computer graphics MN1

Computer graphics MN1 http://www.opengl.org Todays lecture What is OpenGL? How do I use it? Rendering pipeline Points, vertices, lines,, polygons Matrices and transformations Lighting and shading Code