Review: OpenGL

1. Review:OpenGL CIS 681

2. Command Syntax • OpenGL commands start with a gl. • This is followed by the base command such as Color. • Followed by the number of arguments such as 3. • Followed by the type of arguments expected, • such as ffor floats and i for integers • Followed optionally by a v if the arguments are in a vector. • Examples: • glColor3f(1.0,1.0,1.0) • glColor3i(1,1,1) • glColor3iv(vector3i) CIS 681

3. OpenGL is a STATE MACHINE • Set state variables by various OpenGL commands. • Issue commands that are modified by those state variables. • As opposed to parametric commands. • Able to get values of the state variables, e.g., • glGetFloatv(), glGetIntegerv(). • glGetPolygonStipple(). • Able to enable or disable some state variables, e.g., • glEnable() and glDisable. CIS 681

4. OpenGL is Event Driven • auxMainLoop() • Program idles in loop until event occurs • Events • Keystroke • Button depression or release • Mouse movement • Window uncovered or reshaped • Callback routines • Setup to be invoked when specific event occurs CIS 681

5. Graphics Pipeline Vertex (x,y,z,w) eye coordinates Modelview Matrix object coordinates Projection Matrix clip coordinates Perspective Division normalized device coordinates Viewport Transformation glMatrixMode(GL_PROJECTION) glMatrixMode(GL_MODELVIEW) window coordinates CIS 681

6. Transformations Viewing transform Modeling transform Projection transform Viewport transform glLoadMatrix[fd](TYPE *n) glMultMatrix[fd](TYPE *n) glLoadIdentity(void) glMatrixMode(mode) glTranslate[fd](x,y,z) glRotate[fd](angle,x,y,z) glScale[fd](x,y,z) CIS 681

7. Camera gluLookAt(eyex,eyey,eyez,coix,coiy,coiz,upx,upy,upz CIS 681

8. Projection - perspective Orthogonal glOrtho(left,right,bottom,top,near,far) OR gluOrtho2D(left,right,bottom,top) Perspective glFrustum(left,right,bottom,top,near,far) OR gluPerspective(fovy,aspect,zNear,zFar) CIS 681

9. Viewport glViewport(x,y,width,height) CIS 681

10. Matrix Stack glPushMatrix(void) glPopMatrix(void) CIS 681

11. Data • Data can be specified as 2D or 3D • Vertices • glVertex2f(x,y); • glVertex3i(i,j,k); • Rectangles • glRectf(x1,y1,x2,y2); • Polygons CIS 681

12. Drawing Primitives glBegin(GLenum mode) Marks the beginning of a vertex list that describes a geometric primitive. The type of primitive is indicated by mode glEnd(void) Marks the ending of a vertex list. CIS 681

13. Drawing Primitives Valuemeaning GL_POINTS individual points GL_LINES pairs of vertices defining individual lines GL_POLYGON list of vertices forming a polygon GL_QUADS four-tuples of vertices def quadrilateral polygons GL_LINE_STRIP vertices defining a series of line segments (open) GL_LINE_LOOP as above, but defining a closed loop GL_TRIANGLE_STRIP linked strip of triangles GL_TRIANGLE_FAN linked fan of triangles GL_QUAD_STRIP linked strip of quadrilaterals CIS 681

14. Drawing Polygons glBegin(GL_POLYGON); For (i=0, i<n; i++) { angle = i*2*PI/n; x = cos(angle); y = sin(angle); glVertex3f(x,y,1.0); } glEnd(); • glBegin(GL_POLYGON); • glVertex3f(-1.0,1.0,1.0); • glVertex3f(1.0,1.0,1.0); • glVertex3f(1.0,-1.0,1.0); • glVertex3f(-1.0,-1.0,1.0); • glEnd(); CIS 681

15. Drawing Modes glPolygonMode(GL_FRONT,GL_FILL) glFrontFace(GL_CW) glCullFace(GL_BACK) glEnable(GL_CULL_FACE) Normal3f(-1.0,1.0,1.0) CIS 681

16. 2D SET UP glutInit(&argc,argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(width, height); glutInitWindowPosition(100,100); glutCreateWindow(windowTitle); // open the screen window glMatrixMode (GL_PROJECTION); glLoadIdentity(); gluOrtho2D (0,width,0,height); glViewport(0,0,width,height); CIS 681

17. Other Display Topics Clipping planes Display Lists Color State variables Buffers CIS 681