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Viewing and Transformation

Viewing and Transformation. The Camera Analogy 1/2. Set up tripod and pointing the camera at the scene (viewing transformation) . Arrange the scene to be photographed into the desired composition (modeling transformation). The Camera Analogy 2/2.

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Viewing and Transformation

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  1. Viewing and Transformation CGGM Lab. Tan-Chi Ho 2001

  2. The Camera Analogy1/2 • Set up tripod and pointing the camera at the scene (viewing transformation). • Arrange the scene to be photographed into the desired composition (modeling transformation). CGGM Lab. Tan-Chi Ho 2001

  3. The Camera Analogy2/2 • Choose a camera lens or adjust the zoom (projection transformation). • Determine how large you want the final photograph to be (viewport transformation). CGGM Lab. Tan-Chi Ho 2001

  4. Modelview Matrix Modelview Matrix View Transformation Perspective Division Vertex X Y Z W eye coordinates clip coordinates normalized device coordinates window coordinates Object coordinates Overview CGGM Lab. Tan-Chi Ho 2001

  5. Transformations1/12 • The Viewing Transformation • To positioning and aiming the camera. • Use gluLookAt() to indicate where the camera is placed and aimed. • If gluLookAt() was not called, the camera has a default position at the origin, points down the negative Z-axis, and an up-vector of (0, 1, 0). CGGM Lab. Tan-Chi Ho 2001

  6. Transformations2/12 • gluLookAt(GLdouble eyex, GLdouble eyey, GLdouble eyez, GLdouble centerx, GLdouble centery, GLdouble centerz, GLdouble upx, GLdouble upy, GLdoubpe upz); • eyex, eyey, eyez is where the camera is positioned. • centerx, centery, centerz is where the camera look at. • Upx, upy, upz is the up-vector of the camera. CGGM Lab. Tan-Chi Ho 2001

  7. Transformations3/12 • The Modeling Transformation • To position and orient the models. • Rotate, translate, scale and some combination of these operations. • In OpenGL, modeling and viewing transformation are combined into the modelview matrix before the transformation are applied. CGGM Lab. Tan-Chi Ho 2001

  8. Transformations4/12 • glTranslate{fd}(TYPE x,TYPE y,TYPE z); • Multiplies current matrix by a matrix that moves an object by x,y,z • glRotate{fd}(TYPR angle,TYPE x,TYPR y,TYPE z); • Multiplies current matrix by a matrix that rotates an object in a counterclockwise direction about the ray from origin to (x,y,z) with angle as the degrees. CGGM Lab. Tan-Chi Ho 2001

  9. Transformations5/12 • glScale{fd}(TYPE x,TYPE y,TYPE z); • Multiplies current matrix by a matrix that scales an object along axes. CGGM Lab. Tan-Chi Ho 2001

  10. Transformations6/12 • The Projection Transformation • Determine what the field of view(or viewing volume) is and how objects are projected onto the screen. • Two types of projections are provided: • Perspective projection • Orthographic projection CGGM Lab. Tan-Chi Ho 2001

  11. Transformations7/12 • Perspective Projection • glFrustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near, GLdouble far); CGGM Lab. Tan-Chi Ho 2001

  12. Transformations8/12 • gluPerspective(GLdouble fovy, GLdouble aspect, GLdouble near, GLdouble far); CGGM Lab. Tan-Chi Ho 2001

  13. Transformations9/12 • Orthographic Projection • glOrtho(Gldouble left, Gldouble right, Gldouble bottom, Gldouble top, Gldouble near, Gldouble far); • gluOrtho2D(Gldouble left, Gldouble right, Gldouble bottom, Gldouble top); • For 2D projection matrix • The Z coordinates for objects are assumed to lie between –1.0 and 1.0. CGGM Lab. Tan-Chi Ho 2001

  14. Transformations10/12 CGGM Lab. Tan-Chi Ho 2001

  15. Transformations11/12 • The Viewport Transformation • Transform the final image into some region of the window. • The viewport is measured in window coordinates. • glViewport(GLint x, GLint y, GLsizei width, GLsizei height); • Initial values are (0, 0, winWidth, winHeight). CGGM Lab. Tan-Chi Ho 2001

  16. Transformations12/12 • Switch between matrix modes • glMatrixMode(GLenum mode); • Switch between modelview, projection, tecture matrix mode.(GL_MODELVIEW, GL_PROJECTION, GL_TEXTURE) • Current matrix mode is a state variable. • glLoadIdentity(); • Set current matrix to the 4x4 identity matrix. • Always call this after change matrix mode. CGGM Lab. Tan-Chi Ho 2001

  17. The Matrix Manipulation • glLoadIdentity(); • glLoadMatrix{f,d}( const TYPE* m ); • glMultMatrix{f,d}( const TYPE* m ); • glPushMatrix(); • glPopMatrix(); • Stack operation of matrix is very useful for constructing a hierarchical structures. • Ex: a car with four wheels. CGGM Lab. Tan-Chi Ho 2001

  18. Transformation Program1/5 #include <GL/glut.h> static GLfloat year=0.0f, day=0.0f; void init() { glClearColor(0.0, 0.0, 0.0, 0.0); } void GL_display() { // clear the buffer glClear(GL_COLOR_BUFFER_BIT); glColor3f(1.0, 1.0, 1.0); glPushMatrix(); glutWireSphere(1.0, 20, 16); // the Sun glRotatef(year, 0.0, 1.0, 0.0); CGGM Lab. Tan-Chi Ho 2001

  19. Transformation Program2/5 glTranslatef(3.0, 0.0, 0.0); glRotatef(day, 0.0, 1.0, 0.0); glutWireSphere(0.5, 10, 8); // the Planet glPopMatrix(); // swap the front and back buffers glutSwapBuffers(); } void GL_reshape(GLsizei w, GLsizei h) { // viewport transformation glViewport(0, 0, w, h); // projection transformation glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(60.0, (GLfloat)w/(GLfloat)h, 1.0, 20.0); CGGM Lab. Tan-Chi Ho 2001

  20. Transformation Program3/5 // viewing and modeling transformation glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluLookAt(0.0, 3.0, 5.0, // eye 0.0, 0.0, 0.0, // center 0.0, 1.0, 0.0); // up } // GLUT idle function void GL_idle() { day += 10.0; if(day > 360.0) day -= 360.0; year += 1.0; if(year > 360.0) year -= 360.0; // recall GL_display() function glutPostRedisplay(); } CGGM Lab. Tan-Chi Ho 2001

  21. Transformation Program4/5 // GLUT keyboard function void GL_keyboard(unsigned char key, int x, int y) { switch(key) { case 'd': day += 10.0; if(day > 360.0) day -= 360.0; glutPostRedisplay(); break; case 'y': year += 1.0; if(year > 360.0) year -= 360.0; glutPostRedisplay(); break; case 'a': // assign idle function glutIdleFunc(GL_idle); break; case 'A': glutIdleFunc(NULL); break; case 27: exit(0); } } CGGM Lab. Tan-Chi Ho 2001

  22. Transformation Program5/5 int main(int argc, char** argv) { glutInit(&argc, argv); glutInitWindowSize(500, 500); glutInitWindowPosition(0, 0); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); glutCreateWindow("Planet"); init(); glutDisplayFunc(GL_display); glutReshapeFunc(GL_reshape); glutKeyboardFunc(GL_keyboard); glutMainLoop(); } CGGM Lab. Tan-Chi Ho 2001

  23. Any Question? ? CGGM Lab. Tan-Chi Ho 2001

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