Using GLU/GLUT Objects. GLU/GLUT Objects. glucylinder() glutwirecone() GLU/GLUT provides very simple object primitives

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1 Using GLU/GLUT Objects GLU/GLUT provides ver simple object primitives glutwirecone gluclinder glutwirecube GLU/GLUT Objects Each glu/glut object has its default sie, position, and orientation You need to perform modeling transformation to make it right for ou glutwirecube(1.0) - wire means wire frame Put a 111 cube with its center at world (0,0,0) glutwireteapot To create a table top - need to call glscalef(2, 0.1, 2) before ou call glutwirecube(1.0) gluclinder() Three steps to create a clinder sphere, clinder, disk, partial disk 1. Create a GLU quadric object GLUquadricObj *p = glunewquadric(); 2. Set to wire frame mode gluquadricdrawstle(glu LINE); 3. Derive a clinder object from p gluclinder(p,, top, height, slice, stacks) glutwirecone() Use glutwirecone and gluclinder to make a lamp glutwirecone(, height, slices, stacks) - A polgon approimation of a cone. top radius radius height num. of vertical lines num. of horiontal lines The default position is also with at = 0 plane Default position: its at Z = 0 plane : the width of its height: the height of the cone slices: the number of vertical lines used to make up the cone stace: the number of horiontal lines used to make up the cone 1

2 glutwireteapot() The famous Utah Teapot has become an unofficial computer graphics mascot glutwireteapot(0.5) - Transformations Two was to specif transformations (1) Each part of the object is transformed independentl relative to the origin Not the OpenGL Wa! Create a teapot with sie 0.5, and position its center at (0,0,0) Again, ou need to appl transformations to position it at the right spot Translate the b (5,0,0); Translate the lower arm b (5,00); Translate the upper arm b (5,00); Relative Transformation Object Dependenc A better (and easier) wa: (2) Relative transformation: Specif the transformation for each object relative to its parent A graphical scene often consists of man small objects The attributes of an object (positions, orientations) can depend on others A Robot! hammer upper arm lower arm 2

3 Hierarchical Representation - Scene Graph We can describe the object dependenc using a tree structure Relative Transformation Relative transformation: Specif the transformation for each object relative to its parent Root node The position and orientation of an object can be affected b its parent, grand-parent, grand-grand-parent nodes Step 1: Translate and its descendants b (5,0,0); Leaf node This hierarchical representation is referred to as Scene Graph Relative Transformation (2) Step 2: Rotate the lower arm and all its descendants relative to its local ais b -90 degree Relative Transformation (3) Represent relative transformations using scene graph Translate (5,0,0) Rotate (-90) about its local Appl all the wa down Appl all the wa down 3

4 Do it in OpenGL Translate and all its descendants b (5,0,0) Rotate the lower arm and its descendants b -90 degree about the local glmatrimode(gl_modelview); glloadidentit(); // setup our camera gltranslatef(5,0,0); Draw_(); glrotatef(-90, 0, 1, 0); Draw_lower _arm(); Draw_upper_arm(); Draw_hammer(); A more complicated eample How about this model? left hammer Right hammer Scene Graph? (left hammer) (right hammer) Do this and everthing translate (5,0,0) Left hammer rotate 75 degree about the local Right hammer rotate -75 degree about the local Depth-first traversal Program this transformation b depth-first traversal Do transformation(s) Draw (left hammer) (right hammer) Depth First Traversal Do transformation(s) What are the? Draw left arm Do transformation(s) Draw right arm 4

5 How about this? Something is wrong What s wrong? We want to transform the right hammer relative to the, not to the left hammer Translate(5,0,0) Draw Rotate(75, 0, 1, 0) How about this? Do Translate(5,0,0) Draw We should undo the left hammer transformation before we transform the right hammer (left hammer) (right hammer) What s wrong?! Rotate(-75, 0, 1, 0) Do Rotate(75, 0, 1, 0) What s wrong?! Do Rotate(-75, 0, 1, 0) Need to undo this first Undo the previous transformation(s) Need to save the modelview matri right after we draw Initial modelview M Translate(5,0,0) -> M = M T Draw Rotate(75, 0, 1, 0) Rotate(-75, 0, 1, 0) Undo the previous transformation means we want to restore the Modelview Matri M to what it was here i.e., save M right here And then restore the saved Modelview Matri OpenGL Matri Stack We can use OpenGL Matri Stack to perform matri save and restore * Store the current modelview matri Initial modelview M - Make a cop of the current matri and push into OpenGL Matri Stack: Do Translate(5,0,0) -> M = M T call glpushmatri() Draw Do Rotate(75, 0, 1, 0) Do Rotate(-75, 0, 1, 0) - continue to modif the current matri * Restore the saved Matri -Popthe top of the Matri and cop it back to the current Modelview Matri: Call glpopmatri() 5

6 Push and Pop Matri Stack Push and Pop Matri Stack A simple OpenGL routine: push (left hammer) Depth First Traversal pop (right hammer) gltranslate(5,0,0) Draw_(); glpushmatri(); glrotate(75, 0,1,0); Draw_left_hammer(); glpopmatri(); glrotate(-75, 0,1,0); Draw_right_hammer(); Nested push and pop operations Modelview matri (M) glmatrimode(gl_modelview); glloadidentit(); M = I // Transform using M1; M = M1 // Transform using M2; M = M1 M2 glpushmatri(); // Transform using M3 M = M1 M2 M3 glpushmatri();.. // Transform using M4 M = M1 M2 M3 M4 M = M1 M2 M3 glpopmatri(); // Transform using M5 M = M1 M2 M3 M5 glpopmatri(); M = M1 M2 Stack M1M2 M1M2M3 M1 M2 M1 M2 6