Lab 5: object_find_closest()

Objectives

To write and test the object_find_closest() function, where the idea is to:
  1. given the following input: object list, ray base and direction, and the last object hit (could be NULL)
  2. find the object that (a) intersects the ray and (b) is the closest object to the ray base along the ray (smallest t value)
  3. set the (pass-by-reference) distance value to the intersection point and return the pointer to the closest object
The algorithm is as follows:
  1. iterate through the object list, inspecting in turn each object (via list_get_data(objs))
  2. if the object is the same as the last hit object, or the distance to the object/ray intersection is less than 0, skip it (continue;)
  3. otherwise set the currently found closest object and minimum distance to the current object and current distance to the ray/intersection point
Note that the above algorithm is essentially no different from "find the smallest item on the list" problem.

In this lab the material and object lists are also placed within a model_t object which also contains the camera_t object.

Assignment

  1. Use the following prototype for the object_find_closest() function: 
    
object_t* object_find_closest(list_t*,vec_t,vec_t,object_t*,double*);
    and write the body of the function.
  2. You code should be such that the following main.c file works unaltered: 
    
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <math.h>

#include "vector.h"
#include "pixel.h"
#include "list.h"
#include "material.h"
#include "object.h"
#include "model.h"

int main()
{
        model_t         *model;
        object_t        *obj;
        vec_t           pos = { 4.0,  3.0,  5.0};
        vec_t           dir = { 0.0,  0.0, -1.0};
        double          dist;
        FILE            *model_file=NULL, *hits_file=NULL;
    
  if(argc != 3) {
    fprintf(stderr,"Usage: %s  \n",argv[0]);
    exit(1);
  } 
    
  // open model file
  if((model_file = fopen(argv[1],"r")) == NULL) {
     printf("Error opening input file: %s\n",argv[1]);
     return;
  }

  // create model
  model = model_init(model_file);

  // close file
  fclose(model_file);

  // verify that we have all materials
  material_list_print(model->mats,stdout);

  // verify that we have all objects
  object_list_print(model->objs,stdout);

  // open hits file
  if((hits_file = fopen(argv[2],"r")) == NULL) {
     printf("Error opening input file: %s\n",argv[2]);
     return;
  }

 // read direction vectors from hits_file and perform hit comptuations
  while(fscanf(hits_file, "%lf %lf %lf",&dir[0],&dir[1],&dir[2]) == 3) {
    fprintf(stderr,"\n\n");
    vec_print(stderr,"Ray direction:", dir);
    vec_unit(dir,dir);

    obj = object_find_closest(model->objs,pos,dir,NULL,&dist);
    if(dist > 0) {
      fprintf(stderr,"Hit: %-12s ",obj->name);

      fprintf(stderr,"Dist = %8.3lf ",dist);
      vec_print(stderr,"Loc = ",obj->last_hit);
    } else
      fprintf(stderr,"Dist = %8.3lf \n", dist);

    fprintf(stderr, "\n\n");
    obj = object_find_closest(model->objs,pos,dir,obj,&dist);
    if(dist > 0) {
      fprintf(stderr,"Hit: %-12s ", obj->name);

      fprintf(stderr,"Dist = %8.3lf ",dist);
      vec_print(stderr,"Loc = ",obj->last_hit);
    } else
      fprintf(stderr,"Dist = %8.3lf \n", dist);
  }

  // close hits file
  fclose(hits_file);

  return(0);
}
  3. Sample input file model.txt: 
    material green
{
   ambient 0 5 0
}

material yellow
{
   ambient 6 5 0
}

material gray
{
   ambient 4 4 4
}

plane leftwall
{
   material green
   normal 3 0 1
   point  0 0 0
}

plane rightwall
{
   material yellow
   normal -3 0 1
   point  8 0 0
}

plane floor
{
   material gray
   normal 0 1 0
   point  0 0 0
}
  4. Sample input file hittest.txt: 
    -0.5 -0.1 -1
 0.5 -0.1 -1
 0  -0.5 -1.0
 1   1   1
  5. Sample output:
    loaded green 
loaded yellow 
loaded gray 
loaded leftwall 
loaded rightwall 
loaded floor 
material green
{
   ambient 0 5 0
}

material yellow
{
   ambient 6 5 0
}

material gray
{
   ambient 4 4 4
}

plane leftwall
{
   material green
   normal 1 0 0
   point  0 0 0
}

plane rightwall
{
   material yellow
   normal -1 0 0
   point  8 0 0
}

plane floor
{
   material gray
   normal 0 1 0
   point  0 0 0
}



Ray direction:  -0.500  -0.100  -1.000
Hit: leftwall     Dist =    7.633 Loc =    0.600   2.320  -1.800


Hit: floor        Dist =   33.675 Loc =  -11.000   0.000 -25.000


Ray direction:   0.500  -0.100  -1.000
Hit: rightwall    Dist =    7.633 Loc =    7.400   2.320  -1.800


Hit: floor        Dist =   33.675 Loc =   19.000   0.000 -25.000


Ray direction:   0.000  -0.500  -1.000
Hit: floor        Dist =    6.708 Loc =    4.000   0.000  -1.000


Hit: leftwall     Dist =   19.007 Loc =    4.000  -5.500 -12.000


Ray direction:   1.000   1.000   1.000
Dist =   -1.000 


Dist =   -1.000
  6. Note that the program is now run with two arguments: 
    ./main model.txt hittest.txt

Turn in

Turn in all of your code, in one tar.gz archive of your lab05/ directory, including:
  1. A README file containing
    1. Course id--section no
    2. Name
    3. Lab description
    4. Brief solution description (e.g., program design, description of algorithm, etc., however appropriate).
    5. Lessons learned, identified interesting features of your program
    6. Any special usage instructions
  2. Makefile
  3. source code (.h headers and .c source)
  4. object code (do a make clean before tar)

How to hand in

See submit notes.