1. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. CS 497: Computer Graphics James Money

2. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Object Collision What happens if a viewer walks into an object right now?

3. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Object Collision You walk right through the object!

4. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Object Collision What do we need to determine when a view comes in contact with an existing object? We need to determine the intersection of two volumes.

5. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Object Collision However, intersecting objects is an expensive operation. If we operate on bounding volumes, we can make this a simple operation. We just can check the bounding coordinates of the object’s volume!

6. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Object Collision Boolean Intersect(Object1 *obj1,Object2 *obj2){ if ((obj1->minX minX) && (obj1->maxX > obj2->minX)) || ((obj1->minX maxX) &&(obj1->maxX > obj2->maxX)){ if ((obj1->minY minY)&&(obj1->maxY>obj2->minY)) || ((obj1->minY maxY) &&(obj1->maxY>obj2->maxY)){ if ((obj1->minZ minZ) && (obj1->maxZ > obj2->minZ)) || ((obj1->minZ maxZ) &&(obj1->maxZ > obj2->maxZ)){ return TRUE; } if ((obj2->minX minX) && (obj2->maxX > obj1->minX)) || ((obj2->minX maxX) &&(obj2->maxX > obj1->maxX)){ if ((obj2->minY minY)&&(obj2->maxY>obj1->minY)) || ((obj2->minY maxY) &&(obj2->maxY>obj1->maxY)){ if ((obj2->minZ minZ) && (obj2->maxZ > obj1->minZ)) || ((obj2->minZ maxZ) &&(obj2->maxZ > obj1->maxZ)){ return TRUE; } return FALSE; }

7. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Object Collision int Polygon3D::PtInPolygon(Point3D &pt){ double total=pt.x*N->v[0] + pt.y*N->v[1] + pt.z*N->v[2] + N->v[3]; if (fabs(total) > 0.5E-5) return FALSE; int numEdges=0; double tx,ty,tz; for(int I=0;I<(numPoints-1);I++){ tx=(pt.x - pts[I].x)/(pts[I+1].x + pt.x - pts[I].x - maxX); ty=(pt.y - pts[I].y)/(pts[I+1].y + pt.x - pts[I].y - maxY); tz=(pt.z - pts[I].z)/(pts[I+1].z + pt.z - pts[I].z - maxZ); if (((tx>=0.5E-5) && (tx<=1.000005)) && ((ty>=0.5E-5) && (ty<=1.000005)) && ((tz>=0.5E-5) && (tz<=1.000005))) numEdges++; } tx=(pt.x - pts[numPoints-1].x)/ (pts[0].x + pt.x - pts[numPoints-1].x - maxX); ty=(pt.y - pts[numPoints-1].y)/ (pts[0].y + pt.x - pts[numPoints-1].y - maxY); tz=(pt.z - pts[numPoints-1].z)/ (pts[0].z + pt.z - pts[numPoints-1].z - maxZ); if (((tx>=0.5E-5) && (tx<=1.000005)) && ((ty>=0.5E-5) && (ty<=1.000005)) && ((tz>=0.5E-5) && (tz<=1.000005))) numEdges++; if (numEdges & 1) return TRUE; return FALSE; }

8. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Moving Up in the World Now we can detect if the user runs into an object in the world. What about stepping on objects or falling?? For stepping up, we can just check to see if the user’s height/4.0 is greater than the height from where you currently are and the top(Y max ) of the bounding rectangle of the object.

9. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Falling in the world! Now for falling, we have to check to see if the base of of the user object if equal to the base of some object in the world.(Remember in intersection that we don’t check if it’s equal!) We can make it easy by checking the point at the middle of the object on the bottom face of the user.

10. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Falling in the world! To make things easy, we keep a record of the last item you were on top of, and check it first. It the points fits the plane equation for that polygon, we do nothing. If not, we search for a polygon in the current room that has a normal that satisfies this point and save that polygon for next time. If none exists, we drop in world Y coordinates by some value(perhaps 0.2 meters) until we hit a polygon.

11. Copyright  1999 by James H. Money. All rights reserved. Except as permitted under United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the author. Falling in the world! To make things even easier, we will not check an object in the room whose X min, X max, Y min, Y max are not within our X,Y user position at the base.