CS450 – Lect. 2 & 3

1. CS450 – Lect. 2 & 3 Figures and such

2. Pinhole camera model

3. Imaging with pinhole camera

4. Clipping Window

5. Camera Specification • Position • Orientation • Focal length • Film size • (field of view)

6. Sepinski Gasket • Recursively Subdivided Triangle • Approach 1 : Pen-Plotter • Calculate 2-D vertex projection points • Use moveto(x,y) & lineto(x,y) to draw triangles • Apprach 2 : OpenGL, etc. • Specify 3-D vertex positions of object • Specify camera model • System projects lines into 2-D and renders

7. OpenGL Types • Definitions found in gl.h and glu.h // samples … #define Glint int #define GLfloat float

8. Defining Vertices • Coordinate systems • World Coordinates (3-D) • Real numbers and any scale we desire • Device & Screen Coordinates • Integer positions of pixels • Functions that define 2-D & 3-D vertices • glVertex2i(Glint x, Glint y) • glVertex3f(GLfloat x, GLfloat y, GLfloat z) • glVertex3fv(vertex) // vertex[3] contains x,y,z • Etc …

9. Defining an Object Face (shape) • Geometric objects are specified by a sequence of vertices between begin and end function calls • Example: // line segment in 2-D from (x1,y1) to (x2,y2) glBegin(GL_LINES); glVertex2f(x1,y1); glVertex2f(x2,y2); glEnd();

10. OpenGL API Basics • Primitive Functions • Define WHAT (points, line segments, text, …) • Attribute Functions • Define HOW (color, texture, typeface, …) • Viewing Functions • Define CAMERA (location, orientation, clipping, focal length, …) • Transformation Functions • Object MODIFICATION (translation, rotation, scaling, …) • Input Functions • INPUTS (mouse, keyboard, trackball, …) • Control Functions • OpSys interaction (window management, error handling, …)

11. Function Naming • OpenGL • gl*() • Graphics Utility Functions • glu*() • GL Utility Toolkit (GLUT) • glut*() • #include <GL/glut.h>

12. Object Types • GL_LINES // each pair of vertices defines a lines • GL_LINE_STRIP // connected sequence of lines • GL_POLYGON // connected line seq. looping back to start • Must be simple, flat & convex to render correctly • GL_TRIANGLES // each triplet forms triangle • GL_QUADS // each quad of vertices forms quadrangle • GL_TRIANGLE_STRIP //each triplet forms a triangle • GL_QUAD_STRIP // each new vertex pair used with previous pair • GL_TRIANGLE_FAN // each vertex used with previous pair // general format of object definition glBegin( object_type ); glVertex*( … ); glVertex*( … ); … glEnd();

13. Color • Use RGB (additive) color model • Amount of Red, Green & Blue is specified as a value in the range 0.0 … 1.0 • Examples: // to set the current color glColor3f(R,G,B); // to set the clearing (background) color glClearColor(R,G,B,1.0); // the 4th value is opacity 0.0 .. 1.0 // to actually clear the display window glClear();

14. Viewing • Viewing (Clipping) Rectangle • Defines portion of world seeable from camera • Viewing Volume • Defines volume of world that is seeable • Viewing rectangle is the FRONT face of the viewing volume

15. Projections • Orthographic (parallel) • Specifying the viewing volume gluOrtho(left,right,bottom,top,near,far) gluOrtho2D(left,right,bottom,top) • Perspective