SER332 Lecture 11

Introduction to Graphics and Game Development
Projection Transformation
(201804)

Transcript

1. jgs SER332 Introduction to Graphics and Game Development Lecture 11: Projection Transformation Javier Gonzalez-Sanchez javiergs@asu.edu PERALTA 230U Office Hours: By appointment
2. jgs Transformations Projection
3. jgs Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 3 § X, Y and Z axis § A plane (gray) § Several Pyramids (red, green, blue, and white faces) § Use arrows to navigate Let us move to a 3D World
4. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 4 jgs Step 1 Z-buffering. The Z-buffer stores how far a pixel is away from the camera in camera space (normalized device coordinate, more precisely. Typically, it ranges [0, 1]). Limited precision: 16-bit, 24-bit, and 32-bit depth value The Z-buffer is necessary to resolve visibility: a) Clear the z-buffer b) Enable the z-buffer Commands: § glClear( GL_DEPTH_BUFFER_BIT | … colors … ); § glEnable( GL_DEPTH_TEST ); § glutInitDisplayMode( GLUT_DEPTH | … colors … | … double … );
5. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 5 jgs Example // https://github.com/javiergs/SER332/blob/master/Lecture11/main.c // main int main(int argc, char **argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA); glutInitWindowPosition(0, 0); glutInitWindowSize(800, 800); glutCreateWindow("3D"); myInit(); glutSpecialFunc(mySpecial); glutDisplayFunc(myDisplay); glutReshapeFunc(myReshape); glutMainLoop(); return(0); }
6. jgs Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 6 // myInit void myInit() { glShadeModel (GL_SMOOTH); glEnable(GL_DEPTH_TEST); createDrawingList(); } Example
7. jgs Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 7 // myInit void myInit() { glShadeModel (GL_SMOOTH); // glEnable(GL_DEPTH_TEST); createDrawingList(); } Example
8. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 8 jgs Example // myDisplay void myDisplay(void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glViewport(0, 0, width, height); // projection glMatrixMode(GL_PROJECTION); glLoadIdentity(); // to be continue ... }
9. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 9 jgs Step 2 Set the projection: glMatrixMode(GL_PROJECTION); Two Options a) Orthographic Projection b) Perspective
10. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 10 jgs Orthographic Projection glOrtho (left, right, bottom, top, near, far) § Viewing volume is a box. § Objects appear same size irrespective of their distance from the camera. § Use it to show messages
11. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 11 jgs Perspective Projection gluPerspective (fov, aspectratio, near, far) § Viewing volume is a truncated pyramid. § Farther objects appear small and closer objects appear big. § These commands calculates the projection matrix and multiplies the current projection matrix by it.
12. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 12 jgs Example // myDisplay void myDisplay(void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glViewport(0, 0, width, height); // projection glMatrixMode(GL_PROJECTION); glLoadIdentity(); // glOrtho(-10, 10, -10, 10, -10, 10); -- uncomment it to try gluPerspective(45, ratio, 1, 1000); // to be continue ... }
13. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 13 jgs Example
14. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 14 jgs Notes § Changing the distance between the near and far clipping planes can have a big effect on the dimensions of the view volume and the angle of the projectors, making it tricky to set up a reasonable view volume for a given scene. § Where and how to incorporate it into your program? a) Set once per frame (put it in your display function). Some overhead, but safer b) Set once in init function, and update whenever window resizes
15. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 15 jgs Step 3 § Set the camera parameters before you define other transformations to model objects in the scene. § Set camera transformation once per frame (in case you have to move your camera interactively) § Try to restore camera matrix each frame. Do not accumulate the viewing matrix, the accumulation might be skewed due to accumulation of computational errors glMatrixMode(GL_MODELVIEW);
16. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 16 jgs gluLookAt § Viewing transformation can be specified using the command gluLookAt ( eye_x, eye_y, eye_z, center_x, center_y, center_z, up_x, up_y, up_z ) § It encapsulates a series of rotation and translation commands. Viewing transformation can be specified using following commands too. This, however, makes your life harder! § glTranslate {f,d} (x, y, z) § glRotate {f,d} (angle, x, y, z) § glScale {f,d} (x, y, z)
17. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 17 jgs gluLookAt glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluLookAt( 0.0, 1.0, 1.0, /* eye is at (0,1,1) */ 0.0, 1.0, 2.0, /* look at point (0,1,2), viewing direction vector is (0,0,1) */ 0.0, 1.0, 0.0 /* up is in positive Y direction */ );
18. jgs Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 18 // display void myDisplay(void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // projection glViewport(0, 0, width, height); glMatrixMode(GL_PROJECTION); glLoadIdentity(); //glOrtho(-10, 10, -10, 10, -10, 10); gluPerspective(45, ratio, 1, 1000); // view glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluLookAt(x, y, z, x + lx, y + ly, z + lz, 0.0f, 1.0f, 0.0f); // draw glColor3f(0.9f, 0.9f, 0.9f); glBegin(GL_QUADS); // vertex glEnd(); // ... glutSwapBuffers(); }
19. jgs Bonus Display Lists
20. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 20 jgs Creating A Complex Display List // … //create several pyramids GLuint worldDL = glGenLists(1); glNewList(worldDL, GL_COMPILE); for (int i = -3; i < 3; i++) for (int j = -3; j < 3; j++) { glPushMatrix(); glTranslatef(i*10.0, 0, j * 10.0); glCallList(pyramidDL); glPopMatrix(); } glEndList(); // …
21. Javier Gonzalez-Sanchez | SER332 | Spring 2018 | 21 jgs Reading 3D geometric transformation & viewing: § (Required) Read Hearn Baker ch5 p261-p277, p283 – p291 § (Required) Read Hearn Baker ch7 p344-p398, focus on perspective projection (pp 368-383), and 3D viewing in OpenGL (pp 383-389) Z-buffer: § Red Book (pdf): ch10, focus on depth buffer related content § Hearn Baker ch9 p531-p534 Front / Back face culling: § Red Book (pdf): ch2 p43-p44
22. jgs SER332 Introduction to Graphics Javier Gonzalez-Sanchez javiergs@asu.edu Spring 2018 Disclaimer. These slides can only be used as study material for the class SER332 at ASU. They cannot be distributed or used for another purpose.