Lists Display and Transformations
September 16, 2002
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What is a Display List?
w Something like a subroutine.
Rather than repeatedly put in primitives for an object it will allow you to reuse them. Cannot pass parameters to a display list Two steps, compile and call.
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Why use a Display List?
w Efficiency
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Compiling a Display List
glNewList (BOX, GL_COMPILE); (BOX must be a unique identifier) glBegin (insert primitives and attribute calls) glEnd() glEndList();
It is often possible to to gain speed/space advantages A simple change of a display list will change all occurences of the display list Can be transformed and reused multiple times.
w Ease of changee
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w Reusability
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Using a Display List
w glCallList(listID); Often want to isolate a display lists effects: glPushMatrix(); glPushAttrib(GL_ALL_ATTRIB_BITS); glCallList(); glPopAttrib(); glPopMatrix();
A Bigger Example
#include "glut.h" #include <cmath> #include <iostream> using namespace std; void init(); void display(); void menuHandler(int);
static int cubeID, sphereID, tetrahedronID, icosahedronID, currentID;
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Main Program
int main (int argCount, char *argValues[]) { int menuID; glutInit (&argCount, argValues); glutInitDisplayMode ( GLUT_SINGLE | GLUT_RGB); glutInitWindowSize (400, 400); glutInitWindowPosition (100, 100); glutCreateWindow (argValues[0]); init(); glutDisplayFunc (display); }
main (contd)
/* * Build a simple menu */ menuID = glutCreateMenu(menuHandler); glutAddMenuEntry("Cubes", 1); glutAddMenuEntry("Tetrahedron", 2); glutAddMenuEntry("Sphere", 3); glutAddMenuEntry("Isocahedron", 4); glutAddMenuEntry("Exit", 5); glutAttachMenu (GLUT_RIGHT_BUTTON); glutMainLoop ( ); return EXIT_SUCCESS;
init()
void init() { glClearColor(0.0, 0.0, 0.0, 0.0); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-3.0, 3.0, -3.0, 3.0, -10.0, 10.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); /* * It doesn't have to be done here but I'm going * to set up the displayLists at this point. */
init (contd)
cubeID = glGenLists(1); // Draw the cube glNewList(cubeID, GL_COMPILE); glBegin (GL_POLYGON); glVertex3f (-0.5, -0.5, 0.5); glVertex3f ( 0.5, -0.5, 0.5); glVertex3f ( 0.5, 0.5, 0.5); glVertex3f (-0.5, 0.5, 0.5); glEnd(); glBegin (GL_POLYGON); glVertex3f (-0.5, -0.5, -0.5); glVertex3f ( 0.5, -0.5, -0.5); glVertex3f ( 0.5, 0.5, -0.5); glVertex3f (-0.5, 0.5, -0.5); glEnd();
init (contd)
glBegin(GL_POLYGON); glVertex3f glVertex3f (-0.5, (-0.5, glVertex3f (-0.5, glVertex3f (-0.5, glEnd(); glBegin(GL_POLYGON); glVertex3f ( 0.5, glVertex3f ( 0.5, glVertex3f ( 0.5, glVertex3f ( 0.5, glEnd(); -0.5, -0.5); 0.5, -0.5); 0.5, 0.5); -0.5, 0.5);
init (contd)
glBegin(GL_POLYGON); glVertex3f ( -0.5, 0.5, glVertex3f ( 0.5, 0.5, glVertex3f ( 0.5, 0.5, glVertex3f ( -0.5, 0.5, glEnd(); glBegin(GL_POLYGON); glVertex3f ( -0.5,-0.5, glVertex3f ( 0.5,-0.5, glVertex3f ( 0.5,-0.5, glVertex3f ( -0.5,-0.5, glEnd(); glEndList(); -0.5); -0.5); 0.5); 0.5);
-0.5, -0.5); 0.5, -0.5); 0.5, 0.5); -0.5, 0.5);
-0.5); -0.5); 0.5); 0.5);
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init (contd)
sphereID = glGenLists(1); // Draw a sphere. glNewList(sphereID, GL_COMPILE); glutWireSphere(0.5, 10, 10); glEndList(); tetrahedronID = glGenLists(1);// Draw a tetrahedron glNewList(tetrahedronID, GL_COMPILE); glutWireTetrahedron(); glEndList();
init (contd)
icosahedronID = glGenLists(1); glNewList(icosahedronID, GL_COMPILE); glutWireIcosahedron(); glEndList(); currentID = cubeID; }
display
void display (void) { float xoffset, yoffset, zoffset; glClear(GL_COLOR_BUFFER_BIT); for (xoffset = -2.0; xoffset < 3.0; xoffset += 4.0) { for (yoffset = -2.0; yoffset < 3.0; yoffset += 4.0) { for (zoffset = -2.0; zoffset < 3.0; zoffset += 4) { glPushMatrix(); glTranslatef(xoffset,yoffset, zoffset); glCallList(currentID); glPopMatrix(); } } } glFlush(); }
menuHandler
void menuHandler(int itemPicked) { /* * Simple handler that changes color being drawn with. */ switch (itemPi...