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1、OpenGL:Introduction Yanci Zhang Game Programming IIGame Programming II Overview of OpenGL OpenGL vs.Direct X OpenGL“Hello World”GLUT library Rendering pipeline Coordinate system Game Programming IIGame Programming II Outline OpenGL=Open Graphics Library Graphics rendering API Produce high-quality co
2、lor images composed of 3D geometric objects and images Hardware independent Cross platform Game Programming IIGame Programming II What is OpenGL?Bases for many advanced data structures in game programming Typical applications Scene graph State graph Decision tree Kd-tree,quad tree Game Programming I
3、IGame Programming II Basic Function Rendering basic primitives,like points,lines,triangles Matrix operations Local illumination Texture mapping Pixel operations Game Programming IIGame Programming II What Can OpenGL Do?Create windows Handle window events Response to user input Scene management Game
4、Programming IIGame Programming II What Can Not OpenGL Do?OpenGL is only graphics library DirectX handles graphics,audio,user input Use OpenGL improperly,system does nothing Use DirectX improperly,system does something beyond expectation Game Programming IIGame Programming II OpenGL vs.DirectX 1/2 Op
5、enGL Industry standard maintained by OpenGL Architectural Review Board(ARB)Stable function interface Cross platform Very clean,easy to learn DirectX Microsofts product Instable function interface Only support Windows Game Programming IIGame Programming II OpenGL vs.DirectX 2/2 Naming With prefix gl
6、Capital letter for each new word Examples glBegin,glEnd glEnable,glDisable glClear Game Programming IIGame Programming II OpenGL Functions Basic data type With prefix GL All small letters Similar to C+data type Example:GLdouble=double,GLfloat=float,GLint=int,GLuint=unsigned int Constant With prefix
7、GL_ All capital letters Examples:GL_POINTS,GL_CCW Game Programming IIGame Programming II Data Type&Constant Game Programming IIGame Programming II Hello World 1/3#include#include main()initWindow();glClearColor(0.0,0.0,0.0,0.0);glClear(GL_COLOR_BUFFER_BIT);glColor3f(1.0,1.0,1.0);glOrtho(0.0,1.0,0.0,
8、1.0,-1.0,1.0);All opengl programs should include gl.h.Almost all opengl programs include glu.h Initialize window which is a platform-dependent operation Clear windows with black color Use white color to start rendering something on the screen Specify projection matrix Game Programming IIGame Program
9、ming II Hello World 2/3 glBegin(GL_POLYGON);glVertex3f(0.25,0.25,0.0);glVertex3f(0.75,0.25,0.0);glVertex3f(0.75,0.75,0.0);glVertex3f(0.25,0.75,0.0);glEnd();glFlush();Specify the rendering content inside a pair of glBegin/glEnd Execute rendering What we are supposed to see on the screen Does the abov
10、e program really work?At least the window creation is missing Game Programming IIGame Programming II Hello World 3/3 Who is responsible for windows creation and management?GLUT Not a part of OpenGL Perform system-level I/O with the host operating system Allow creation of cross-platform code Make lea
11、rning OpenGL easier Game Programming IIGame Programming II OpenGL Utility Toolkit 1/2 Main Functions Window definition Window control Monitoring keyboard and mouse input Drawing a number of geometric primitives Limitation:glutMainLoop()A function which never returns Hard to integrate GLUT into a pro
12、gram which wants to control its own event loop Process is terminated when window is closed Game Programming IIGame Programming II OpenGL Utility Toolkit 2/2 1.Create window 2.Initialize OpenGL 3.Register callback functions Rendering callback function Window resize callback function User input callba
13、ck function 4.Enter main loop Infinite loop Game Programming IIGame Programming II GLUT Framework Game Programming IIGame Programming II Example:GLUT 1/6#include#include void main(int argc,char*argv)int mode=GLUT_RGB|GLUT_DOUBLE;glutInitDisplayMode(mode);glutInitWindowSize(500,500);glutCreateWindow(
14、Simple);init();glutDisplayFunc(display);glutKeyboardFunc(key);glutMainLoop();Game Programming IIGame Programming II Example:GLUT 2/6#include#include void main(int argc,char*argv)int mode=GLUT_RGB|GLUT_DOUBLE;glutInitDisplayMode(mode);glutInitWindowSize(500,500);glutCreateWindow(Simple);init();glutDi
15、splayFunc(display);glutKeyboardFunc(key);glutMainLoop();Configure the display mode Game Programming IIGame Programming II Example:GLUT 3/6#include#include void main(int argc,char*argv)int mode=GLUT_RGB|GLUT_DOUBLE;glutInitDisplayMode(mode);glutInitWindowSize(500,500);glutCreateWindow(Simple);init();
16、glutDisplayFunc(display);glutKeyboardFunc(key);glutMainLoop();Create a(500,500)window named“Simple”Game Programming IIGame Programming II Example:GLUT 4/6#include#include void main(int argc,char*argv)int mode=GLUT_RGB|GLUT_DOUBLE;glutInitDisplayMode(mode);glutInitWindowSize(500,500);glutCreateWindow
17、(Simple);init();glutDisplayFunc(display);glutKeyboardFunc(key);glutMainLoop();Initialization(optional)Game Programming IIGame Programming II Example:GLUT 5/6#include#include void main(int argc,char*argv)int mode=GLUT_RGB|GLUT_DOUBLE;glutInitDisplayMode(mode);glutInitWindowSize(500,500);glutCreateWin
18、dow(Simple);init();glutDisplayFunc(display);glutKeyboardFunc(key);glutMainLoop();Register user-defined callback functions Game Programming IIGame Programming II Example:GLUT 6/6#include#include void main(int argc,char*argv)int mode=GLUT_RGB|GLUT_DOUBLE;glutInitDisplayMode(mode);glutInitWindowSize(50
19、0,500);glutCreateWindow(Simple);init();glutDisplayFunc(display);glutKeyboardFunc(key);glutMainLoop();Enter infinite loop of OpenGL Game Programming IIGame Programming II Events Queue Event queue Keyboard Mouse Window .Mouse_callback().Keypress_callback().window_callback().MainLoop()glutDisplayFunc(m
20、yDisplayFunc);/register callback void myDisplayFunc(void)/implementation of callback glClear(GL_COLOR_BUFFER_BIT);glBegin(GL_TRIANGLE);glEnd();glFlush();Rendering callback void glutDisplayFunc(void(*func)(void);Implement rendering task in this function A must in GLUT Game Programming IIGame Programm
21、ing II Important GLUT Callbacks 1/5 Window resize callback void glutReshapeFunc(void(*func)(int width,int height);Called when window size is changed Common operations:modify OpenGL matrix,viewport width,height is the new width and height of window respectively Game Programming IIGame Programming II
22、Important GLUT Callbacks 2/5 Keyboard input callback void glutKeyboardFunc(void(*func)(unsigned char key,int x,int y);key is the ascii character of pressed key;(x,y)indicates mouse position when key is pressed Game Programming IIGame Programming II Important GLUT Callbacks 3/5 void keyboard(unsigned
23、 char key,int x,int y)switch(key)case q:case Q:exit(EXIT_SUCCESS);break;case r:case R:rotate=GL_TRUE;glutPostRedisplay();break;Mouse input callback void glutMouseFunc(void(*func)(int button,int state,int x,int y);Called when mouse button is pressed or released button is one of GLUT_LEFT_BUTTON,GLUT_
24、RIGHT_BUTTON,GLUT+MIDDLE_BUTTON;state is either GLUT_UP or GLUT_DOWN;(x,y)indicates mouse position when mouse button state changed Game Programming IIGame Programming II Important GLUT Callbacks 4/5 Idle callback void glutIdleFunc(void(*func)(void);Offer a mechanism for doing animation Game Programm
25、ing IIGame Programming II Important GLUT Callbacks 5/5 void idle(void)t+=dt;glutPostRedisplay();Input:scene objects,lighting,camera Most of the data is vertex list Output:pixels stored in framebuffer Question:how to convert 3D vertex list to 2D pixels?OpenGL is designed to fulfill this task Game Pro
26、gramming IIGame Programming II OpenGL Pipeline OpenGL Pipeline Main task:transformation and lighting Transformation:Model-View transformation:translation,rotation,scaling Projection transformation:perspective,parallel Lighting Fixed-pipeline implements per-vertex lighting Lighting is normally delaye
27、d to fragment processing in programmable pipeline Game Programming IIGame Programming II Vertex Processing Assemble vertices into primitives Lines/Curves Triangles/Polygons/Surfaces Game Programming IIGame Programming II Primitive Assembly Dont render invisible objects Clipping Remove primitives out
28、side of the cameras view frustum Backface culling Remove triangles facing away from camera Usually cuts down$of triangles by about 50%Game Programming IIGame Programming II Clipping and Culling Convert a primitive into a set of fragments Each pixel has both RGB color and depth Interpolate vertex col
29、or over fragments Fragment might not correspond to pixels on screen:Occluded fragments Game Programming IIGame Programming II Rasterization Assemble fragments into final framebuffer Hidden-surface removal:Some fragments may occlude parts of others Z-buffer sorts pixels by distance Handle transparenc
30、y Other operations Game Programming IIGame Programming II Fragment Processing Using vertex list to represent a set rendering primitives 14 primitives supported by OpenGL Point:GL_POINTS Line:GL_LINES,GL_LINE_STRIP,GL_LINE_LOOP Triangle:GL_TRIANGLES,GL_TRIANGLE_STRIP,GL_TRIANGLE_FAN Polygon:GL_QUADS,
31、GL_QUAD_STRIP,GL_POLYGON Game Programming IIGame Programming II Rendering Primitives Polygons must obey following rules Simple polygon Convex polygon Coplanar vertices Triangle satisfies all the above rules Most common rendering primitive Game Programming IIGame Programming II Restriction on Polygon
32、s Game Programming IIGame Programming II Specifying Vertex 1/2 Type of rendering primitive and its vertices have to be specified Vertices specification must be inside a pair of glBegin()/glEnd()Specify rendering primitive when glBegin()is called Game Programming IIGame Programming II Specifying Vert
33、ex 2/2 void drawParallelogram(GLfloat color)glBegin(GL_QUADS);glColor3fv(color);glVertex2f(0.0,0.0);glVertex2f(1.0,0.0);glVertex2f(1.5,1.118);glVertex2f(0.5,1.118);glEnd();GL_POINTS Point size can be modified by glPointSize(float size)Game Programming IIGame Programming II Rendering Primitive:Point
34、glBegin(GL_POINTS);glColor3fv(color);glVertex2f(P0.x,P0.y);glVertex2f(P1.x,P1.y);glVertex2f(P2.x,P2.y);glVertex2f(P3.x,P3.y);glVertex2f(P4.x,P4.y);glVertex2f(P5.x,P5.y);glVertex2f(P6.x,P6.y);glVertex2f(P7.x,P7.y);glEnd();GL_LINES Represented by a pair of vertices Width of line can be specified by gl
35、LineWidth(float width)Game Programming IIGame Programming II Rendering Primitive:Line glBegin(GL_LINES);glColor3fv(color);glVertex2f(P0.x,P0.y);glVertex2f(P1.x,P1.y);glVertex2f(P2.x,P2.y);glVertex2f(P3.x,P3.y);glVertex2f(P4.x,P4.y);glVertex2f(P5.x,P5.y);glVertex2f(P6.x,P6.y);glVertex2f(P7.x,P7.y);gl
36、End();GL_LINE_STRIP Open line segment represented by a set of connected lines No line from P7 to P0 Game Programming IIGame Programming II Rendering Primitive:Line glBegin(GL_LINE_STRIP);glColor3fv(color);glVertex2f(P0.x,P0.y);glVertex2f(P1.x,P1.y);glVertex2f(P2.x,P2.y);glVertex2f(P3.x,P3.y);glVerte
37、x2f(P4.x,P4.y);glVertex2f(P5.x,P5.y);glVertex2f(P6.x,P6.y);glVertex2f(P7.x,P7.y);glEnd();GL_LINE_LOOP Closed line segments represented by a set of connected lines Note the line from P7 to P0 Game Programming IIGame Programming II Rendering Primitive:Line glBegin(GL_LINE_LOOP);glColor3fv(color);glVer
38、tex2f(P0.x,P0.y);glVertex2f(P1.x,P1.y);glVertex2f(P2.x,P2.y);glVertex2f(P3.x,P3.y);glVertex2f(P4.x,P4.y);glVertex2f(P5.x,P5.y);glVertex2f(P6.x,P6.y);glVertex2f(P7.x,P7.y);glEnd();GL_POLYGON Simple convex polygon Polygon is filled with the specified color Game Programming IIGame Programming II Render
39、ing Primitive:Polygon glBegin(GL_POLYGON);glColor3fv(color);glVertex2f(P0.x,P0.y);glVertex2f(P1.x,P1.y);glVertex2f(P2.x,P2.y);glVertex2f(P3.x,P3.y);glVertex2f(P4.x,P4.y);glVertex2f(P5.x,P5.y);glVertex2f(P6.x,P6.y);glVertex2f(P7.x,P7.y);glEnd();GL_TRIANGLES Every three vertices form a triangle 3*N ve
40、rtices represent N triangles Redundant vertices are ignored Game Programming IIGame Programming II Rendering Primitive:Triangle glBegin(GL_TRIANGLES);glColor3fv(color);glVertex2f(P0.x,P0.y);glVertex2f(P1.x,P1.y);glVertex2f(P2.x,P2.y);glVertex2f(P3.x,P3.y);glVertex2f(P4.x,P4.y);glVertex2f(P5.x,P5.y);
41、glVertex2f(P6.x,P6.y);glVertex2f(P7.x,P7.y);glEnd();GL_TRIANGLE_STRIP N+2 vertices represent N triangles Odd triangle i formed by vertex i,i+1,i+2 Even triangle i formed by vertex i+1,i,i+2 Game Programming IIGame Programming II Rendering Primitive:Triangle glBegin(GL_TRIANGLE_STRIP);glColor3fv(colo
42、r);glVertex2f(v0.x,v0.y);glVertex2f(v1.x,v1.y);glVertex2f(v2.x,v2.y);glVertex2f(v3.x,v3.y);glVertex2f(v4.x,v4.y);glVertex2f(v5.x,v5.y);glVertex2f(v6.x,v6.y);glVertex2f(v7.x,v7.y);glEnd();v0 v2 v1 v3 v4 v5 v6 v7 GL_TRIANGLE_FAN N+2 vertices represent N triangles Triangle i formed by vertex 1,i+1,i+2
43、Game Programming IIGame Programming II Rendering Primitive:Triangle glBegin(GL_TRIANGLE_FAN);glColor3fv(color);glVertex2f(v0.x,v0.y);glVertex2f(v1.x,v1.y);glVertex2f(v2.x,v2.y);glVertex2f(v3.x,v3.y);glVertex2f(v4.x,v4.y);glVertex2f(v5.x,v5.y)glEnd();v0 v1 v2 v3 v4 v5 GL_QUADS Every four vertices for
44、m a quad Game Programming IIGame Programming II Rendering Primitive:Quad glBegin(GL_QUADS);glColor3fv(color);glVertex2f(P0.x,P0.y);glVertex2f(P1.x,P1.y);glVertex2f(P2.x,P2.y);glVertex2f(P3.x,P3.y);glVertex2f(P4.x,P4.y);glVertex2f(P5.x,P5.y);glVertex2f(P6.x,P6.y);glVertex2f(P7.x,P7.y);glEnd();The bas
45、ic rendering command in OpenGL Only a few OpenGL functions can be called inside a glBegin()/glEnd()pair Describing vertex properties glVertex,glColor,glTexCoord,glNormal Game Programming IIGame Programming II glBegin()/glEnd()How to convert 3D objects to 2D image?Just like taking a photograph!Game P
46、rogramming IIGame Programming II Camera Analogy 1/2 camera tripod model viewing volume Projection transformations Adjust the lens of the camera Viewing transformations Tripoddefine position and orientation of the viewing volume in the world Modeling transformations Moving the model Viewport transfor
47、mations Enlarge or reduce the physical photograph Game Programming IIGame Programming II Camera Analogy 2/2 Steps in Forming an Image Specify geometry(world coordinates)Specify camera(camera coordinates)Project(clip coordinates)Map to viewport(screen coordinates)Each step uses transformations Every
48、transformation is equivalent to a change in coordinate systems Game Programming IIGame Programming II Coord.Sys.and Transformations Game Programming IIGame Programming II Coord.Sys.and Transformations Object Coordinates World Coordinates Camera Coordinates Clip Coordinates Screen Coordinates Model T
49、ransformation World Transformation Project Transformation Viewport Transformation Game Programming IIGame Programming II Affine Transformations 1/2 Definition Using a single matrix multiplication to represent affine transformation by using augmented matrix and augmented vector Preserving geometry li
50、nes,polygons,quadrics Affine=line preserving Rotation,translation,scaling Projection Concatenation(composition)Game Programming IIGame Programming II Affine Transformations 2/2 Each vertex is a column vector w is usually 1.0 (x,y,z,w)=(ax,ay,az,aw)If w is not 1.0,we can recover x,y,z by division by