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Chapter 4/5

Chapter 4/5. glMatrixMode Modeling Transformations glTranslate quick look at glPushMatrix and glPopMatrix glScale reflection glRotate composing transformations placing multiple objects. MJBBasicTransformations.cpp. Notice display list for createshape

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Chapter 4/5

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  1. Chapter 4/5 glMatrixMode Modeling Transformations glTranslate quick look at glPushMatrix and glPopMatrix glScale reflection glRotate composing transformations placing multiple objects

  2. MJBBasicTransformations.cpp • Notice display list for createshape • note use of glPushMatrix() and glPopMatrix for isolating transformations for stroke text and transformed shape.

  3. MJBBasicTransformations.cpp • rotation • scaling • translation

  4. Multiple rotation experiment • work in pairs: • Both, place book face up so you can read it. • Person 1, rotate 90 degrees around z-axis, then rotate 180 degrees around y axis. • Person 2, rotate 180 degrees around y axis, then rotate 90 degrees around z-axis. • Compare.

  5. Multiple rotation experiment Conclusions: Order Matters!

  6. PROJECTION and MODELVIEW Matrices • GL_MODELVIEW is for organizing the pieces of the picture - building the model. • GL_PROJECTION is for setting viewing box and type of projection for viewing.

  7. PROJECTION and MODELVIEW Matrices • GL_MODELVIEW is for organizing the pieces of the picture - building the model. • drawing: glBegin, glutSphere,.... • GL_PROJECTION is for setting viewing box and type of projection for viewing. • glOrtho, glFrustum

  8. PROJECTION and MODELVIEW Matrices • Both matrices are alway active and being used. • We can only change or set one at a time. • To modify one we have to put it in the "matrix modifying machine", eg • glMatrixMode(GL_PROJECTION); • glMatrixMode(GL_MODELVIEW);

  9. PROJECTION and MODELVIEW Matrices • To make sure we start with a clean slate: glLoadIdentity(); • Any new changes are made to the matrix that is currently "in Mode". • The current state of both is used for whatever is being drawn.

  10. PROJECTION Matrix glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho... or glFrustum... This is usually in resize routine, but it can be modified in display routine. Remember to then return to the MODELVIEW matrix, glMatrixMode(GL_MODELVIEW);

  11. Modeling Transformations • Run box.cpp • In resize: glMatrixMode(GL_PROJECTION); glLoadIdentity(); glFrustum(-5.0, 5.0, -5.0, 5.0, 5.0, 100.0); glMatrixMode(GL_MODELVIEW);

  12. box.cpp • in drawScene glLoadIdentity(); // Modeling transformations. glTranslatef(0.0, 0.0, -15.0); glutWireCube(5.0); // Box. //A 5x5 cube, centered at the origin

  13. Moving the box into view

  14. glTranslatef( p, q, r) • translate (x,y,z) to (x+p,y+q,z+r); • Reminder - away from your eye is NEGATIVE z direction.

  15. boxWPushPop.cpp //Apply glTranslatef only to glutWireCube glPushMatrix(); glTranslatef(0.0, 0.0, -15.0); glutWireCube(5.0); // Box. glPopMatrix();

  16. boxV2.cpp //Modeling Transformations glTranslatef(0.0, 0.0, -15.0); ... glScalef(.7,2.0,3.0); Run boxV2.cpp

  17. boxV2.cpp Black box is • First scaled (while at the origin) • Then translated.

  18. glScalef(u,v,w); maps (x, y, z) of an object to (u*x, v*y, w*z)

  19. Reflection • glScale(1.0, -1.0, 1.0); • Run boxV3.cpp. press m to see before and after reflection. Notice toggle.

  20. boxV4.cpp //Modeling Transformations glTranslatef(0.0, 0.0, -15.0); ... glRotatef(60.0, 0.0,0.0,1.0); glutWireTeapot(3.0); Run and look at boxV4.cpp

  21. boxV4.cpp glRotatef(60.0, 0.0,0.0,1.0); Counterclockwise rotation looking from • origin to (0,0,1) or • (0,0,1) to origin?

  22. boxV4.cpp glRotatef(60.0, 0.0,0.0,1.0); Counterclockwise rotation looking from • origin to (0,0,1) or • (0,0,1) to origin?

  23. glRotatef(A, p, q, r) • rotate around the vector (p, q, r) • A is the angle • in degrees, counterclockwise • looking from the point (p, q, r) toward the origin

  24. Transformations • Run the experiments in the book. Think through the answer before you run it.

  25. Composing Transformations • run boxV5.cpp, draw on board • Key input t: glTranslatef(10.0,0.0,0.0); glRotatef(45.0, 0.0,0.0,1.0); glutWireCube(5.0); • Key input r: glRotatef(45.0, 0.0,0.0,1.0); glTranslatef(10.0,0.0,0.0); glutWireCube(5.0);

  26. Placing multiple objects • Do experiment with Powerpoint:

  27. Trotate.cpp //Modeling Transformations glTranslatef(0.0, 0.0, -15.0); ... glRotatef(60.0, 0.0,0.0,1.0); glBegin(GL_LINES); glVertex3f(0, 0, 0); glVertex3f(3, 0, 0); glVertex3f(3, -1, 0); glVertex3f(3, 1, 0); glEnd(); Run and look at Trotate.cpp

  28. boxV6.cpp • original - a box and a sphere • draw on board • m: translate together • o: say translate then rotate, but really rotate then translate • Check out the code! • try ortho and frustrum

  29. pushPopDemo.cpp Any transformations (rotate,translate, scale) put inside a glPushMatrix() and a glPopMatrix() pair are ignored outside that pair. Other statements (color, draw something,...) are NOT ignored

  30. pushPopDemo.cpp Any transformations (rotate,translate, scale) put inside a glPushMatrix() and a glPopMatrix() pair are ignored outside that pair. Other statements (color, draw something,...) are NOT ignored

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