3D/!AU_Attack/source/c/engine

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/*
   engine.c : Written by Greg Scott   1997
   for Acorn User, as part of the "Virtual
   Worlds" series.

   Usage of the source code is done at the
   owners risk, and Acorn User or the auth
   or hold no responsibility for damages.
*/

/* AUTHORS NOTE: A lot of the code in here is very complex, and can never be adequately explained. PLEASE PLEASE contact me for more assistance, it is much easier to address personal problems with the ideas than in general.

AUThreeD@aol.com

or contact the Acorn User offices and they will pass it on. Thank you. */

/* ANSI C includes */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/* OTHER includes */

#include "our_lib.h"


/* DEFINES */

#define WORLD_WIDTH 64 /* This is the number of walls across in our world */
#define WORLD_HEIGHT 64 /* This is the number of walls down in our world */
#define WALL_WIDTH 64 /* This is the width of each wall in pixels */
#define WALL_HEIGHT 64 /* This is the height of each wall in pixels */
#define WALL_NUMBER 20 /* This defines the number of walls allowed */
#define CELL_X_SIZE 64 /* this is the size in units of each cell */
#define CELL_Y_SIZE 64 /* this is the size in units of each cell */
#define CELL_X_SIZE_FP 6 /* this is used in binary shifting */
#define CELL_Y_SIZE_FP 6 /* this is used in binary shifting */
#define FOUND_WALL 1 /* this flag is used to indicate when an intersection has be found */
#define MAX_DISTANCE 4000 /* this defines the largest distance a ray could travel in the world, used for look up tables */
#define STEP_LENGTH 15 /* this new define holds how far forward and backwards the viewpoint moves each time */
#define CLOSEST 50 /* this stores the closest a player can walk into a wall */

/* NEW use of ANGLES variables, they are now not defines but are inputted by the command line at the beginning of main()*/

int ANGLE_0,ANGLE_6,ANGLE_30,ANGLE_90,ANGLE_180,ANGLE_270,ANGLE_360;

int VERTICAL_SCALE;
int SCREEN_HEIGHT,SCREEN_WIDTH;
/*
#define ANGLE_0 0
#define ANGLE_6 30
#define ANGLE_30 160
#define ANGLE_90 480
#define ANGLE_270 1440
#define ANGLE_360 1920
#define ANGLE_180 960*/
/* GLOBAL variables */

char world[WORLD_HEIGHT+1][WORLD_WIDTH+1];/* This holds our text data file */
char objects[WORLD_HEIGHT+1][WORLD_WIDTH+1]; /* NEW object array (as world)*/
char walls[WALL_NUMBER+1][(WALL_WIDTH*WALL_HEIGHT)+1];
char objgraphics[WALL_NUMBER+1][(WALL_WIDTH*WALL_HEIGHT)+1];
/* This holds the wall graphics in a two dimensional array */
/* Note the usage of char and not "int" in both cases. This is because a char is 8 bytes, which gives 256 colours (used in our Mode 13 screen) and also an integer up to 256, when our text file doesn't go over 20 in number! Hence there is no need for an int array in either case. */

char *screen_address; /* this will hold the base of the screen memory which we will manipulate. By altering values in the screen memory, we alter what appears on the screen. Note that this is of type "char *" because it holds the memory address of a byte array - the 256 colour mode 13 screen (well it will do!) */
char *screen_address_bank; /* this is another pointer to the other area of screen memory which we will be using for SCREEN BANKING - avoiding flickering of the screen during animating graphics */
char *screen_address_temp; /* this is a spare pointer for use during the switching of the two above values */

/* these new FIXED POINT INTEGER pointers point to look-up tables used in the ray casting engine. These are explained of in the engine, but the look-ups are generated in aua_tables() */

int *tan_table,*inv_tan_table; /* pointers to tangent look_ups */
int *y_step,*x_step;           /* pointers to more complex look_ups */
int *inv_cos_table,            /* sin/cos tables (look_ups)    */
    *inv_sin_table;
int *cos_table;                /* cosinal look_up table    */
int *recip_table;              /* reciprocal table used instead of a division
. See later */

int *dx_table,                 /* NEW FIXED POINT tables for moving the */
    *dy_table;                 /* view point very quickly */
     /* used to store scale values of each sliver*/
/* FUNCTION definitions */

/* this function generates LOOK UP tables - arrays holding pre-calculated trigonometric variables used in the ray casting process */

void aua_tables(void)
{

int ang, /* this is used to hold values while making look-ups */
    angt; /* same */

float rad_angle; /* this holds the radians equivalent of the fixed point angle system (0-1920 = 0-360 degrees = 0-6.whatever radians. Next month I'll be changing the system so it becomes 0-1800 instead of 1920, this will allow a slightly smaller screen width, more like Wolfenstein, this will lead to an increase in frame rate. Yes! */

/* dynamically allocated adequate memory for the look-ups */
tan_table     = (int *)malloc(sizeof(int) * (ANGLE_360+1));
inv_tan_table = (int *)malloc(sizeof(int) * (ANGLE_360+1));

y_step        = (int *)malloc(sizeof(int) * (ANGLE_360+1));
x_step        = (int  *)malloc(sizeof(int) * (ANGLE_360+1));

cos_table     = (int  *)malloc(sizeof(int) * (ANGLE_360+1));
inv_cos_table = (int  *)malloc(sizeof(int) * (ANGLE_360+1));
inv_sin_table = (int  *)malloc(sizeof(int) * (ANGLE_360+1));
/* new table, for the engine, to avoid using a divide */
recip_table   = (int  *)malloc(sizeof(int) * (MAX_DISTANCE+1));
/* new tables for moving the view point */
dx_table      = (int  *)malloc(sizeof(int) * (ANGLE_360+1));
dy_table      = (int  *)malloc(sizeof(int) * (ANGLE_360+1));
/* generate them, their use is explained in the ray casting engine */

for(angt=ANGLE_0;angt<=ANGLE_360;angt++)
{
ang=angt;
/* this next line calculates the radian angle to pass to the trig. functions */
rad_angle=(float)((3.272e-4) + ang * 2*3.141592654/ANGLE_360);

tan_table[ang]=(int)(tan(rad_angle)*65536);
inv_tan_table[ang]=(int)((1/tan(rad_angle))*65536);
/* note tha above conversions to fixed point integers */

/* we do the same for these tables, but unfortunately at the asymptotes the numbers become awkwardly large to store in our fixed point representation. Instead of multiplying by 64 we do 8, to make sure that no overflow can occur at this stage. We only need to multiply by another 8 later in the engine, its okay */

if(ang>=ANGLE_0 && ang<ANGLE_180)
{
y_step[ang]=fabs( (8) * (tan_table[ang]) );
}
else
  y_step[ang]=-fabs( (8) * (tan_table[ang]) );

if(ang>=ANGLE_90 && ang<ANGLE_270)
{
x_step[ang]=-fabs( (8) * (inv_tan_table[ang]) );
}
else
{
x_step[ang]=fabs( (8) * (inv_tan_table[ang]) );
}

/* conversion to fixed point */
inv_cos_table[ang]=(int)((1/cos(rad_angle))*65536);
inv_sin_table[ang]=(int)((1/sin(rad_angle))*65536);

/* work out tables for moving the viewpoint */
dx_table[ang]=(int)(cos(6.28*ang/ANGLE_360)*STEP_LENGTH)*65536;
dy_table[ang]=(int)(sin(6.28*ang/ANGLE_360)*STEP_LENGTH)*65536;
}

/* the cosine table is used to get rid of the "fish bowl effect", explained in the ray caster. Basically we work out cosines for our own span of vision, from -30 degrees to +30 degrees. This means that as we scan from left to right, or vice versa, our rays of light are actually cast out in a cartesian, circular way. Our world is however square, polar, so we have to acknowledge the distortion caused by mixing cartesian and polar coordinates. In this look up we also have a bit of scaling in it, yet more time saving !!! */

for(ang=-ANGLE_30;ang<=ANGLE_30;ang++)
{
/* work out radians to pass to cosine function */
rad_angle=(float)((3.272e-4)+ ang * 2*3.141592654/ANGLE_360);

/*fixed point conversion */
cos_table[ang+ANGLE_30]=(int)(VERTICAL_SCALE/(cos(rad_angle))*65536);
}

/* this creates a reciprocal table, so we don't have to use divides. Multiplying by the reciprocal of a number is the same as dividing by it: After all,

8 / 4 = 2 and 8 * 0.25 (1 over 4) = 2 - they produce the same result */

for(ang=1;ang<MAX_DISTANCE;ang++)
{
  /* it is still fixed point though */
  recip_table[ang]=(int)(1.0/(float)ang*65536);
}

}

/* this function is the heart of the program, the engine, to generate the first person view */
void aua_raycaster(int view_x,int view_y,int view_angle)
{
/* remember that we are thinking in 2-D, not in 3D when we discuss ideas. Below does not mean "a floor below", it really means "behind", but we say below because we are imagining looking down on the view point to form a 2-D plan */

/* this function, for each column of the 320 pixel width Mode 13 screen, casts out two rays. One ray looks for X, horizontal intersections with walls, and the other tracks intersections with Y, vertical wall boundaries. After all, the only time a collision could occur is on a boundary of a cell, as the wall fills up the entire cell. Expect to see lots of 64's, though remember that this ray caster is very routine, and has not at all been put through my "box of magic". The engine will become much more personalised very soon! */



int cell_x, /* used to store which cell of the walls data the ray is in */
cell_y, /* " */
casting=2, /* used to store if ray casting has finished */
x_hit_type, /* this stores the wall type hit by the x casting ray */
y_hit_type, /* this sotres the wall type (number) hit by the y ray */
x_bound, /* this holds the next x boundary for a possible intersection */
y_bound, /* this holds the next y boundary for a possible intersection */
next_y_cell, /* this is used to figure out the quadrant of the ray (+/-)*/
next_x_cell, /* " */
x_delta, /* this is +'d to the x_bound var. to move to the next boundary */
y_delta, /* this is +'d to the y_bound var. to move to the next boundary */
xi_save, /* this stores where the x casting ray made its intersection */
yi_save, /* this stores where the y casting ray made its intersection */
scale,   /* this stores the scale of the sliver to be drawn in each column */
ray, /* this stores the ray number being cast out (0-320)*/
xray, /* this flag is used to show if casting is over */
yray, /* " */
dist_x, /* this holds the distance to the x intersection */
dist_y; /* this holds the distance to the y intersection */

int xi,
      yi,
      xadd,
      yadd; /* these are used to accurately trace and move each ray */


int variables[5]; /* this is used to pass variables to a super fast sliver render */

int xtrans_dist, /* these NEW TRANSPARENT variables are used for windows */
    ytrans_dist, /* each one will be used later to draw transparent walls*/
    xtrans_col,
    ytrans_col,
    xtrans_type,
    ytrans_type,
    xtrans_done,/* these last two are used as flags to mark if a transpar-*/
    ytrans_done;/*ency has been found or not */

/* firstly, we set up the variables[] we already know, such as screen_address, walls and the screen height we are using. These are all things which our sliver renderer needs to know to plot its column */

variables[0]=(char *)screen_address;
variables[2]=SCREEN_HEIGHT;

/* now we get down to the nitty gritty. Here we subtract 30 degrees from the viewing angle remember that our FOV is 60 degrees which means that we cast from -30 to +30 */

if ( (view_angle-=ANGLE_30) < 0)
   {
   /* this ensures that we don't go over or under 0/360 degrees! */
   view_angle=ANGLE_360 + view_angle;
   }
/* now we start the main loop, start at the right of the screen (319), and cast each column one by one to the left */

for (ray=SCREEN_WIDTH-1; ray>=0; ray--)
    {
/* for each ray to be cast we actually cast out two rays : one to check for vertical boundary collisions and the other to check for horizontal boundary collisions. Considering that walls fill up each cell, we need only look for intersections on the boundaries. We have to perform seperate cast because just casting one ray complicates the matter and it doesn't give much speed increase, if any. */

/* NEW LINE : We have to check to see if the viewing angle is at the asymptotes, unfortunately the fixed point system cannot store the values held at these angles, so we have to avoid their use. This is not very elegant I know, but it saves a lot of head aches and no one can tell we've done it! */

if(view_angle==ANGLE_0 || view_angle==ANGLE_90 || view_angle ==ANGLE_180 || view_angle==ANGLE_270)view_angle++;
/* SECTION 1 : CALCULATING THE FIRST X and Y INTERSECTIONS*/
/* Once we have done this the following intersections are easy*/


/* The X CASTING RAY : here we test to see if the angle of the ray is facing upwards. We need to know which halfplane we're casting from relative to the y-axis. */


 if (view_angle >= ANGLE_0 && view_angle < ANGLE_180)
       {
/* if so then we assign variables to that effect. We must compute the first horizontal line that could be intersected with the ray. Note : it will be above the viewer.*/

y_bound = (CELL_Y_SIZE + (view_y & 0xffc0)); /* this line is merely an optimized version of CELL_Y_SIZE + (view_y % 64). I use it many times in this engine. */

y_delta = CELL_Y_SIZE; /* this means that for every movement of the ray, the y boundary moves up one cell, which it would. It is the delta to get to the next horizontal line */

/* next we use the inverse tan function to calculate the initial position of the x boundary searching ray on its first intersection. We have to use tan because it is related to slopes */

/* NEW FIXED POINT CALCULATION of
xi = (float)(inv_tan_table[view_angle] * (y_bound - view_y)) +view_x; */

xi=((y_bound-view_y))*(inv_tan_table[view_angle]);
xi+=(view_x<<16);

/* this means that the quadrant of the ray is not negative, that is the next y boundary will appear above the view point and not below (in terms of looking down on the viewer). This is the cell delta */
next_y_cell = 0;

       }
/* if the viewing angle is greater than 180 degrees and less than 270 degrees then we have to do other calculations (lower half plane) */
    else
       {
/* we know that because the viewing angle is downwards, so then the horizontal intersection has to be BELOW the viewer */
y_bound = (int)(view_y & 0xffc0);

/* because of this we also know that the next Y intersections will be a cell below each other. So the delta for each horizontal intersection will be a cell below  the last */
y_delta = -CELL_Y_SIZE;

/* we again use the tangent function, just as before, to calculate the first x intersection with a boundary. */

/* NEW FIXED POINT, I won't show the old lines any more */

xi=((y_bound-view_y))*(inv_tan_table[view_angle]);
xi+=(view_x<<16);

/* and we know also that the quadrant is below the player, so the cell y delta will be negative */

next_y_cell = -1;

       }
/* Y RAY : we do similar calculations but this time to calculate the first y intersections */

/* we test to see if the view angle is within the vertical asymptotes of 360 degrees. We need to know which halfplane we're casting from relative to the x-axis. */

if (view_angle < ANGLE_90 || view_angle >= ANGLE_270)
       {
/* we can deduce certain things, just as with the x ray. We know that because the view angle is to the right, the next X boundary (which is constant) will be to the RIGHT of the viewer. */
x_bound = (int)(CELL_X_SIZE + (view_x & 0xffc0));

/* notice this recurring optimization of view_x % 64 */

/* and we also know that each vertical cell boundary after the first will be a cell's width away */

x_delta = CELL_X_SIZE;
/* this time we use the tangent function (not the inverse tan) to calculate where the first y boundary intersection will occur). */

/* NEW FIXED POINT */

yi=((x_bound - view_x))*(tan_table[view_angle]);
yi+=(view_y<<16);
/* and we know also that because the view is positive, the next_x_cell delta does not need to be negative */

next_x_cell = 0;

       }
/* otherwise, if the viewing angle is towards the other direction...*/
    else
       {
/* we know that the first x boundary can occur only to the left of the viewer because the ray angle is facing left. So we can do view_x % 64 to calculate the first vertical boundary, this should be becoming obvious */
x_bound = (int)(view_x & 0xffc0);

/* we also know that the delta for the cell will be to the left, each time the ray moves to the next boundary the next vertical intersection will be a cell to the left than the last. */
x_delta = -CELL_X_SIZE;

/* we use the tangental function again to calculate the position on the horizontal intersections */

/* NEW FIXED POINT */

yi=((x_bound - view_x))*(tan_table[view_angle]);
yi+=(view_y<<16);
/* and we also know that the x cell value will be minus, because as the ray moves to another cell, because the ray is going left, the value must be minus. */
next_x_cell = -1;

       }

/* Now we have performed the slightly tricky task of the first intersections, we can move on to calculating the next ones. This is more simple, as we know that the intersections can only occur at cell boundaries.*/

/* SECTION 2 : Testing for further intersections */

/* these flags store if casting of both rays is complete */
xray=yray=xtrans_done=ytrans_done=0;

/* X Ray is first */
/* because we are testing for each next intersection, we can figure out more easily the following intersections. */
/* this is a look up table holding the next y intercepts, based on the tangental function and the size of cells. Basically we add this to the ray each time we move it a bit more, searching for a wall at a cell boundary */

/* NEW FIXED POINT, note the shift 3 times to the left, the equivalent of a multiply by 8, this takes no time, and really I don't know why I've done it like this! It works. */

xadd=y_step[view_angle]<<3;

/* start casting the x ray */
while(!xray)
{
/* compute current cell position of the ray to inspect*/

cell_x = ( (x_bound+next_x_cell) >> CELL_X_SIZE_FP);
/* Note we have to shift not only by 6, but also by 16 to convert BACK to normal maths */
cell_y = (int)yi>>22;

/* both of the above examples use binary shifting to achieve a divide by 64. Cell_y computation uses identical techniques to those covered in the magazine. Cell_x is calculated by using the x_bound and next_x_cell values calculated beforehand. */

if(cell_x<0)cell_x=0;if(cell_x>63)cell_x=63;
if(cell_y<0)cell_y=0;if(cell_y>63)cell_y=63;
/* these simple lines ensure that the ray doesn't go out of the world, though they aren't really needed. */

/* we look up in the world file to see if there is a wall at the intersection of our ray */
if ((x_hit_type =world[cell_y][cell_x])!=0)
{
 /* or any (extra or different) tile value you wish */
if(x_hit_type==9 || x_hit_type==7){
  /*THEN THE WALL IS TRANSPARENT!!!*/
 xtrans_dist=((yi-(view_y<<16))>>8)*(inv_sin_table[view_angle]>>8);
 xtrans_type=x_hit_type;
 xtrans_col=((int)(yi>>16) & 0x003f);
 xtrans_done=FOUND_WALL;
/* we record all required details then continue */
                 }

else
{
/* if so we calculate the distance to it using the old O-Level technique of using sine and cosine instead of doing the standard PYTHAGORAS technique.*/

/* NEW FIXED POINT calculation, notice that in this next line we have both a conversion TO fixed point (view_y) and also the check against over flow is very apparent, we share the accuracy. See the article for more details */

dist_x  = ( (yi - (view_y<<16))>>8) * (inv_sin_table[view_angle]>>8);
/* we also save the exact position of the intersection because we will need it later to add texture mapping. */

/* We save yi after converting it back to normal maths */

yi_save = (int)yi>>16;

/* because the x ray has found a wall, we can stop casting */
xray=FOUND_WALL;

}
}

{
/* if not, we compute the next possible intersection */
yi +=xadd; /* FIXED POINT ADDITION requires no extra work */
x_bound += x_delta; /* and we also calculate the next horizontal boundary, which we know will be x_delta away, no need for complex workings. */
}

}
/* SECTION 3 */
/* WE NOW do exactly the same but for the yray, we cast it out, check for a wall, if there is one we take the distance to it etc, if not, we move  the ray until a wall it found. */

/* look up the value to add to the ray each time we move it */

/* See above for more information, this is FIXED POINT remember */
yadd=x_step[view_angle]<<3;

/* start casting the ray */
while(!yray)
{

/* compute current cell to inspect */

/* Because XI IS IN FIXED POINT we have to not only divide by 64 but also we have to convert BACK to normal maths */

cell_x = (int)xi>>22;
cell_y = ( (y_bound + next_y_cell) >> CELL_Y_SIZE_FP);
/* these calculations work out which cells the ray is in, ready to check for walls in the world[][] array. They both use binary shifting to perform divide by 64's. */

/* check that the ray has not gone out of the world, though this isn't really necessary */
if(cell_x<0)cell_x=0;if(cell_x>63)cell_x=63;
if(cell_y<0)cell_y=0;if(cell_y>63)cell_y=63;

/* look and see if there is a wall at the current point of intersection */
if ((y_hit_type = world[cell_y][cell_x])!=0)
{
if(y_hit_type==9 || y_hit_type==7){
  /*THEN THE WALL IS TRANSPARENT!!!*/
ytrans_dist=((xi-(view_x<<16))>>8)*(inv_cos_table[view_angle]>>8);
ytrans_type=y_hit_type;
ytrans_col=((int)(xi>>16) & 0x003f);
ytrans_done=FOUND_WALL;
}
/* we record all required details then continue */

else
{



/* Use the old O-Level triangle method of calulating distance using cos, rather than using PYTHAGORAS, which is slower because it uses a square root! */
/* FIXED POINT calculation, just the same as the inv_sin calculation see above. */
dist_y  = ( (xi - (view_x<<16))>>8) * (inv_cos_table[view_angle]>>8);

/* save the exact intersection point, we will need it later */
/* Same as aobve, very simple conversion back from FIXED POINT to normal maths */
xi_save = (int)xi>>16;
/* STOP y casting in that case, a wall has been found. */
yray=FOUND_WALL;
}
}

{
/* if not, move the ray on */
xi+=yadd; /* AGAIN, no extra work is required for FIXED POINT ADDITION */
y_bound += y_delta; /* and move to the next vertical boundary position */
}

}

/* SECTION 4*/
/* Both rays have been cast, both rays have met a wall, we now need to see which is closer, and then plot it correctly. */

/* find out which wall (x or y) is nearer the viewer. */

/* we have altered this distance checking line to avoid minus distances being selected to draw, which produces large spikes on the screen! Again this is because of fixed point */

    if (dist_x < dist_y && dist_x>0 || dist_y<0)

       {


/* we need to take into account here, when computing the scale of the vertical strip (sliver) to be drawn, a phenemenon (of sorts) known as the "fish bowl effect". This is caused by mizing of cartesian and polar coordinates. To get rid of it we use the cosine function. I have combined other multiplies of a vertical scaling factor with the cosine transformation to save time. All we eventually be explained. You could replace the line with scale=13312/dist_x++ and see what weird results you get! */

/* NEW NEW NEW : We have fixed point here, and using the reciprocal table (see around) we don't have to do a length divide! Notice how we convert dist_x back to normal to index the recip_table array, and that all accuracy is lost with the cos_table, because all its figures are above zero (see aua_tables) and also that we actually convert the whole answer back to normal maths for scale */

scale = (int)( (cos_table[ray]>>16) * (recip_table[dist_x>>16]) >>16);

/* assign the variables we need to the variables to be passed to the ASM sliver renderer (super fast!) */

variables[3]=scale-1; /*stores the scale of the strip (height of it)*/
variables[4]=ray; /* we use ray as the x position to plot to (0-319)*/
variables[1]=&walls[x_hit_type][(yi_save & 0x003f)];

/* and we call the assembler function (explained at a later date)*/
ourlib_sliver(&variables[0]);

       }
/* else the dist_y was nearer, everything from above applies */
    else
       {

/* avoid fish bowl effect and scale properly with FIXED POINT clever bits!, see above */
scale = (int)( (cos_table[ray]>>16) * (recip_table[dist_y>>16]) >> 16);


/* set up variables for our sliver engine, see above */

variables[3]=scale-1; /*stores the scale of the strip (height of it)*/
variables[4]=ray; /* we use ray as the x position to plot to (0-319)*/
variables[1]=&walls[y_hit_type+1][(xi_save & 0x003f)];

/* notice we add one to the wall graphic selection, so the darker tile is used for added variation. See the article for more details of this sort of shading, if you want to call it that! */

/* call our sliver engine */
ourlib_sliver(&variables[0]);

       }
/* it is here that we draw the overlaying transparent wall */
if(xtrans_done && xtrans_dist<dist_y)
{
  scale=(int)((cos_table[ray]>>16) * (recip_table[xtrans_dist>>16])>>16);
  variables[3]=scale-1;
  variables[4]=ray;
  variables[1]=&walls[xtrans_type][xtrans_col];

/* now call our special function which treats color 0 as a mask */

ourlib_sliver_mask(variables);

}
else if(ytrans_done && ytrans_dist<dist_x)
{
  scale=(int)((cos_table[ray]>>16) * (recip_table[ytrans_dist>>16])>>16);
  variables[3]=scale-1;
  variables[4]=ray;
  variables[1]=&walls[ytrans_type+1][ytrans_col];

/* now call our special function which treats color 0 as a mask */

ourlib_sliver_mask(variables);

}




/* this ray has been finished. Increase the angle of the next ray and start again! */

    if (++view_angle>=ANGLE_360)
       {
       /* this ensures that the ray angle doesn't go over 360 degrees! */
       view_angle=0;

       }
/* ray loop */
    }
/* end ray caster engine */
/* objects*/
}



/* this function grabs all the different walls from a single file */

void aua_graphics(void)
{
int x, /* this is used to store the x coordinate of a point on the screen */
    y, /* this is used to store the y coordinate of a point on the screen */
    wall_number; /* this will be used to index the walls[x][] char array */

/* first of all we get the graphics file <AUARay$Dir>.graphics onto the screen */

system("*ScreenLoad <AUARay$Dir>.graphics");

/* next we start grabbing each tile, 64 x 64 pixels, into the walls[][] array */

/* we use this large for loop at the ourlib_bitmap_grab function to invidually grab each tile into its own walls[x][] array slot, note that we CAN'T HAVE WALL 0 as this represents a gap in the world! */

ourlib_killcursor(); /* get rid of cursor first */

for(wall_number=1,y=0;y<256/*SCREEN_HEIGHT*/;y+=WALL_HEIGHT)for(x=0;x<320/*SCREEN_WIDTH*/;x+=WALL_WIDTH,wall_number++)
{
/* this calls the function ourlib_bitmap_grab (I said it would be handy!) which grabs the area of screen memory marked by the first four parameters, stores it in the byte array pointer in parameter five, reading it all from the screen pointed to by screen_address */

ourlib_bitmap_grab(x,y,x+WALL_WIDTH-1,y+WALL_HEIGHT-1,&walls[wall_number][0],screen_address);

/* this makes sure we don't go over our number of walls limit */

if(wall_number>=WALL_NUMBER)break;
}

/* new stuff load in objects separately */
/* see above for comments (its identical) */
system("*ScreenLoad <AURay$Dir>.Objgraphic");
ourlib_killcursor();

for(wall_number=1,y=0;y<256/*SCREEN_HEIGHT*/;y+=WALL_HEIGHT)for(x=0;x<320/*SCREEN_WIDTH*/;x+=WALL_WIDTH,wall_number++)
{
ourlib_bitmap_grab(x,y,x+63,y+63,&objgraphics[wall_number][0],screen_address);
if(wall_number>WALL_NUMBER)break;
}


}

/* this function loads in the data from our world text file and stores it in the world[][] array */

void aua_world(void)
{

FILE *world_file; /* we need a file pointer as we will be loading in text */

int row, /* this will be used to index the world[][] array */
    column; /* this will be used to index the world[][] array */

char ch; /* this is used to store each number as it is loaded in */

/* open the world file, if it is not there then exit the program */

if(!(world_file=fopen("<AUARay$Dir>.world","r")))exit(1);

/* this program loads in the data from the world file, row by row, column by column using the getc() ANSI function */

for(row=0;row<WORLD_HEIGHT;row++)
{
for(column=0;column<WORLD_WIDTH;column++)
{
while((ch=getc(world_file))==10){} /* this filters out any mess, though not often used! */

if(ch==' ')ch=0; /*this ensures the correct value is stored, if there is a gap in the file, this means a space in the world, a zero */
else ch=ch-'0';

/* this new line will (should!) convert letters into their appropriate number */

if(ch>16)ch-=6;

world[(WORLD_HEIGHT-1)-row][column]=ch; /* this finally stores the value in the correct position */

/*printf("%d",ch); uncomment this line to see the world data loaded in */
}
/*printf("\n"); uncomment this line to see the world data loaded in */
}

/* when all is done, close the file */
fclose(world_file);

/* new part to load in object data, see above for comments */

if(!(world_file=fopen("<AUARay$Dir>.objworld","r"))) exit(1);
for(row=0;row<WORLD_HEIGHT;row++)
{
  for(column=0;column<WORLD_WIDTH;column++)
  {
  while((ch=getc(world_file))==10){}
  if(ch==' ')ch=0;
  else ch=ch-'0';
  if(ch>16)ch-=6;
  objects[(WORLD_HEIGHT-1)-row][column]=ch;
  }
}
fclose(world_file);

}


/* NEWER MAIN function .

All changes are commented */

void main(int argc,char *argv[])
{
  int view_x, /* this holds the viewing x coordinate */
      view_y, /* this holds the viewing y coordinate */
      view_angle; /* this holds the viewing angle in fixed units 0-1920 */

  int key_press, /* this is used to confirm input of values */
      done=0,    /* flag to indicate if the user wants to quit */
      dx,        /* movement variables for the viewer */
      dy,
      y_cell,    /* these NEW variables are used to store the player/viewer*/
      x_cell,    /* world positions, for calculating viewer hitting walls */
      y_sub_cell,
      x_sub_cell,
      time_start,
      time_finish, /* These last few variables are used to work out */
      frames=0,    /* the frames per sec. of the system, slow for now! */
      door_x,
      door_y;      /* These new variables will be used for door things */

/* NEW system of passing, we use the standard argc and argv to supply parameters to the engine. FIRST we must extract them:*/

/* check that correct number of parameters have been passed */

if(argc!=8)
{
/* quit if not */
printf("Error: Incorrect number of parameters passed. _Exiting\n"); exit(1);
/* "beep" (on most machines)*/ putchar('\a');
}
/* use atoi to get it right */
/* INPUT ALL VALUES FROM COMMAND LINE using ATOI and then work out needed*/
/* angle values for the ray casting engine. */
view_x=atoi(argv[1]);view_y=atoi(argv[2]);view_angle=atoi(argv[3]);
SCREEN_WIDTH=atoi(argv[4]);SCREEN_HEIGHT=atoi(argv[5]);
ANGLE_360=atoi(argv[6]);ANGLE_180=ANGLE_360/2;ANGLE_90=ANGLE_180/2;
ANGLE_6=(int)ANGLE_360/60;ANGLE_30=(int)ANGLE_90/3;ANGLE_0=0;
ANGLE_270=ANGLE_90*3;VERTICAL_SCALE=atoi(argv[7]);
/* DONE. Now continue as normal with the program */


/* now we call aua_world to load in the text world file which defines our walls type and layout */

printf("loading in text file <AUARay$Dir>.world\n");
aua_world();

/* check to see if the viewer is inside a game cell WALL, which would be bad news! */

if(world[view_y>>6][view_x>>6])
{
  printf("Bad coordinates given, viewer is IN a WALL!, exiting\n");
  exit(1);
}

/* now we call aua_tables to generate some look-up tables for the engine to use, look-ups are explained up at the top of the file next to the global variables */

printf("calling aua_tables() this could take a long time on some machines\n");
/* newer fixed point version */
aua_tables();

/* all is done in terms of input for now. We need to switch to Mode 13 */

printf("Switching to Mode 13\n");

/* call ourlib_changemode to switch to mode 13 */

ourlib_changemode(13);

/* call ourlib_findscreen to get the screen base address of mode 13,  without the correct address we can't draw anything and the computer could crash */

screen_address=(char *)ourlib_findscreen();
/* NEW LOAD TITLE SCREEN */
system("*ScreenLoad <AUARay$Dir>.title");ourlib_killcursor();
ourlib_wait(200);
/*ourlib_screen_dissolve(screen_address,81920); USE IF WANTED */

/* THEN WAIT THEN SCREENDISSOLVE OUT, see above */

/* now we need to *screenload our graphics file, and grab each individual wall graphic one by one, the function aua_graphics does this */

aua_graphics();


/* NOW we call setup_screens, a small function which helps with banking */
/* With all the data loaded in we shall try and initiate SCREEN BANKS. First we change to MODE 15, so that screen memory becomes available for two times MODE 13 */

ourlib_setup_screens();
ourlib_changemode(15);

/* Now we switch to MODE 13, and get the first screen address */

ourlib_changemode(13);
ourlib_killcursor();
/*os_clg();*/
screen_address=(char *)ourlib_findscreen();

/* Now we switch to the other screen bank and get the other screen address */

ourlib_simpleswitch();

screen_address_bank=(char *)ourlib_findscreen();
ourlib_slowclear(screen_address_bank,81920,0);
ourlib_killcursor();
/* Switch back to the other screen */

ourlib_simpleswitch();

/* NOW we can call setup background, to tell the screen clearer the colour of the floor and ceilings we want.*/

ourlib_setup_background(208,45);

/* NOW we can start the main loop, exitable only by pressing the Q key. Use the Cursors to move the viewpoint around */
/* We shall also take a reading to work out the frame rate of the system, slow for now */

/* NEW ADJUSTING LINES : we add an offset to both screen memory areas in order to centre the image in the middle of the screen no matter what size */

screen_address+=(320-SCREEN_WIDTH)>>1;
screen_address_bank+=(320-SCREEN_WIDTH)>>1;

ourlib_killcursor(); /* get rid of the cursor flashing away */
time_start=ourlib_gettime();

while(!done) /* the loop will continue until done */
{

 ourlib_fastclg_two(screen_address,SCREEN_WIDTH,SCREEN_HEIGHT); /* we call the floor/ceiling function to colour the whole screen */
/* then we call the ray caster to draw over it */
  aua_raycaster(view_x,view_y,view_angle);

/* reset the variables for moving the viewpoint */

dx=dy=0;

/* now we test for different key presses and take action accordingly */

if(ourlib_keydown(16)==255)done=1; /* if Q is pressed then quit */

/* LEFT */
if(ourlib_keydown(121)==255)
{
  if((view_angle-=ANGLE_6)<ANGLE_0)
  view_angle=ANGLE_360;
}

/*RIGHT */
if(ourlib_keydown(25)==255)
{
  if((view_angle+=ANGLE_6)>ANGLE_360)
  view_angle=ANGLE_0;
}
/* UP and DOWN */
if(ourlib_keydown(57)==255)
{
  dx=dx_table[view_angle];
  dy=dy_table[view_angle];
}

if(ourlib_keydown(41)==255)
{

  dx=-dx_table[view_angle];
  dy=-dy_table[view_angle];
}

/* NOW we need to move the player and recalculate the cell the viewer is in, and ALSO check to see if the player has hit a wall */

/* Watch for the conversions of fixed point and things */

/* Player X actually is in normal maths */
 view_x= (int)((view_x<<16)+dx)>>16;
 view_y= (int)((view_y<<16)+dy)>>16;

/* NEW OPTIMIZED VERSIONS OF MOVING THE PLAYER */

 x_cell = view_x>>6;
 y_cell = view_y>>6;

 x_sub_cell = view_x & 0x003f;
 y_sub_cell = view_y & 0x003f;

/* CHECK to see if player has walked into walls */
 if ((dx>>8)>0 ){
 if ((world[y_cell][x_cell+1] != 0)  && (x_sub_cell>(CELL_X_SIZE-CLOSEST)))
                {
                view_x-= (x_sub_cell-(CELL_X_SIZE-CLOSEST ));
                }
                }
 else
 {
 if ( (world[y_cell][x_cell-1] != 0)  && (x_sub_cell < (CLOSEST) ) )
                {
                view_x+= (CLOSEST-x_sub_cell) ;
                }
 }

 if ((dy>>8)>0 ){
 if ( (world[(y_cell+1)][x_cell] != 0)  &&
                (y_sub_cell > (CELL_Y_SIZE-CLOSEST ) ) )
                {
                view_y-= (y_sub_cell-(CELL_Y_SIZE-CLOSEST ));
                }
                }
 else
 {
 if ( (world[(y_cell-1)][x_cell] != 0)  && (y_sub_cell < (CLOSEST) ) )
                {
                view_y+= (CLOSEST-y_sub_cell);
                }
 }



/* NEW DOOR code. A "probe" is sent out in front of the player, if a door tile is found near it then the block is destroyed. */

if(ourlib_keydown(98)==255)
{
/* Use similar techniques to above to find door */

dx=dx_table[view_angle];
dy=dy_table[view_angle];

/* Calculate door x and y, it is in normal maths */
 door_x= (int)((view_x<<16)+(dx<<3))>>16;
 door_y= (int)((view_y<<16)+(dy<<3))>>16;

/* NEW OPTIMIZED VERSIONS OF FINDIN DOORS */
/* now find the cell we are looking in with the standard equation */

 x_cell = (int)door_x>>6;
 y_cell = (int)door_y>>6;

/* Check if a doors is present */

if(world[y_cell][x_cell]==7 /* OR WHATEVER YOU LIKE */)
{
world[y_cell][x_cell]=0; /* or alternatively do what you like */
}
}




/* PHEW! Now we can wait for a vysnc and then switch the views/banks over ot  produce flicker-free animation */
ourlib_waitvsync();
ourlib_simpleswitch();

/* We also have to switch the memory addresses around so our functions draw to the correct memory */

screen_address_temp=screen_address_bank;
screen_address_bank=screen_address;
screen_address=screen_address_temp;

/* add one to the frames count, we are counting the number of frames generated  */
frames++;
}
/* record the time stopped */

time_finish=ourlib_gettime();

/* take a screenshot, using *screen save, and save it inside the directory */

system("*ScreenSave <AUARay$Dir>.scrshot");

/* close down the screens using an ourlib function */

ourlib_closedown_screens();

/* change to mode 15 and bring back the cursor just in case */

ourlib_changemode(15);
ourlib_revivecursor();

/* print the calculation and other info. */
printf("******* FRAMES PER SECOND ********\n%f",(float)frames/(float)((time_finish-time_start)/100));
}

00000000  2f 2a 0a 20 20 20 65 6e  67 69 6e 65 2e 63 20 3a  |/*.   engine.c :|
00000010  20 57 72 69 74 74 65 6e  20 62 79 20 47 72 65 67  | Written by Greg|
00000020  20 53 63 6f 74 74 20 20  20 31 39 39 37 0a 20 20  | Scott   1997.  |
00000030  20 66 6f 72 20 41 63 6f  72 6e 20 55 73 65 72 2c  | for Acorn User,|
00000040  20 61 73 20 70 61 72 74  20 6f 66 20 74 68 65 20  | as part of the |
00000050  22 56 69 72 74 75 61 6c  0a 20 20 20 57 6f 72 6c  |"Virtual.   Worl|
00000060  64 73 22 20 73 65 72 69  65 73 2e 0a 0a 20 20 20  |ds" series...   |
00000070  55 73 61 67 65 20 6f 66  20 74 68 65 20 73 6f 75  |Usage of the sou|
00000080  72 63 65 20 63 6f 64 65  20 69 73 20 64 6f 6e 65  |rce code is done|
00000090  20 61 74 20 74 68 65 0a  20 20 20 6f 77 6e 65 72  | at the.   owner|
000000a0  73 20 72 69 73 6b 2c 20  61 6e 64 20 41 63 6f 72  |s risk, and Acor|
000000b0  6e 20 55 73 65 72 20 6f  72 20 74 68 65 20 61 75  |n User or the au|
000000c0  74 68 0a 20 20 20 6f 72  20 68 6f 6c 64 20 6e 6f  |th.   or hold no|
000000d0  20 72 65 73 70 6f 6e 73  69 62 69 6c 69 74 79 20  | responsibility |
000000e0  66 6f 72 20 64 61 6d 61  67 65 73 2e 0a 2a 2f 0a  |for damages..*/.|
000000f0  0a 2f 2a 20 41 55 54 48  4f 52 53 20 4e 4f 54 45  |./* AUTHORS NOTE|
00000100  3a 20 41 20 6c 6f 74 20  6f 66 20 74 68 65 20 63  |: A lot of the c|
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00000220  54 68 61 6e 6b 20 79 6f  75 2e 20 2a 2f 0a 0a 2f  |Thank you. */../|
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00000750  36 2c 41 4e 47 4c 45 5f  33 30 2c 41 4e 47 4c 45  |6,ANGLE_30,ANGLE|
00000760  5f 39 30 2c 41 4e 47 4c  45 5f 31 38 30 2c 41 4e  |_90,ANGLE_180,AN|
00000770  47 4c 45 5f 32 37 30 2c  41 4e 47 4c 45 5f 33 36  |GLE_270,ANGLE_36|
00000780  30 3b 0a 0a 69 6e 74 20  56 45 52 54 49 43 41 4c  |0;..int VERTICAL|
00000790  5f 53 43 41 4c 45 3b 0a  69 6e 74 20 53 43 52 45  |_SCALE;.int SCRE|
000007a0  45 4e 5f 48 45 49 47 48  54 2c 53 43 52 45 45 4e  |EN_HEIGHT,SCREEN|
000007b0  5f 57 49 44 54 48 3b 0a  2f 2a 0a 23 64 65 66 69  |_WIDTH;./*.#defi|
000007c0  6e 65 20 41 4e 47 4c 45  5f 30 20 30 0a 23 64 65  |ne ANGLE_0 0.#de|
000007d0  66 69 6e 65 20 41 4e 47  4c 45 5f 36 20 33 30 0a  |fine ANGLE_6 30.|
000007e0  23 64 65 66 69 6e 65 20  41 4e 47 4c 45 5f 33 30  |#define ANGLE_30|
000007f0  20 31 36 30 0a 23 64 65  66 69 6e 65 20 41 4e 47  | 160.#define ANG|
00000800  4c 45 5f 39 30 20 34 38  30 0a 23 64 65 66 69 6e  |LE_90 480.#defin|
00000810  65 20 41 4e 47 4c 45 5f  32 37 30 20 31 34 34 30  |e ANGLE_270 1440|
00000820  0a 23 64 65 66 69 6e 65  20 41 4e 47 4c 45 5f 33  |.#define ANGLE_3|
00000830  36 30 20 31 39 32 30 0a  23 64 65 66 69 6e 65 20  |60 1920.#define |
00000840  41 4e 47 4c 45 5f 31 38  30 20 39 36 30 2a 2f 0a  |ANGLE_180 960*/.|
00000850  2f 2a 20 47 4c 4f 42 41  4c 20 76 61 72 69 61 62  |/* GLOBAL variab|
00000860  6c 65 73 20 2a 2f 0a 0a  63 68 61 72 20 77 6f 72  |les */..char wor|
00000870  6c 64 5b 57 4f 52 4c 44  5f 48 45 49 47 48 54 2b  |ld[WORLD_HEIGHT+|
00000880  31 5d 5b 57 4f 52 4c 44  5f 57 49 44 54 48 2b 31  |1][WORLD_WIDTH+1|
00000890  5d 3b 2f 2a 20 54 68 69  73 20 68 6f 6c 64 73 20  |];/* This holds |
000008a0  6f 75 72 20 74 65 78 74  20 64 61 74 61 20 66 69  |our text data fi|
000008b0  6c 65 20 2a 2f 0a 63 68  61 72 20 6f 62 6a 65 63  |le */.char objec|
000008c0  74 73 5b 57 4f 52 4c 44  5f 48 45 49 47 48 54 2b  |ts[WORLD_HEIGHT+|
000008d0  31 5d 5b 57 4f 52 4c 44  5f 57 49 44 54 48 2b 31  |1][WORLD_WIDTH+1|
000008e0  5d 3b 20 2f 2a 20 4e 45  57 20 6f 62 6a 65 63 74  |]; /* NEW object|
000008f0  20 61 72 72 61 79 20 28  61 73 20 77 6f 72 6c 64  | array (as world|
00000900  29 2a 2f 0a 63 68 61 72  20 77 61 6c 6c 73 5b 57  |)*/.char walls[W|
00000910  41 4c 4c 5f 4e 55 4d 42  45 52 2b 31 5d 5b 28 57  |ALL_NUMBER+1][(W|
00000920  41 4c 4c 5f 57 49 44 54  48 2a 57 41 4c 4c 5f 48  |ALL_WIDTH*WALL_H|
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00000950  5f 4e 55 4d 42 45 52 2b  31 5d 5b 28 57 41 4c 4c  |_NUMBER+1][(WALL|
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00000980  68 6f 6c 64 73 20 74 68  65 20 77 61 6c 6c 20 67  |holds the wall g|
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00000b30  20 42 79 20 61 6c 74 65  72 69 6e 67 20 76 61 6c  | By altering val|
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00000b50  6e 20 6d 65 6d 6f 72 79  2c 20 77 65 20 61 6c 74  |n memory, we alt|
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00000bd0  61 72 72 61 79 20 2d 20  74 68 65 20 32 35 36 20  |array - the 256 |
00000be0  63 6f 6c 6f 75 72 20 6d  6f 64 65 20 31 33 20 73  |colour mode 13 s|
00000bf0  63 72 65 65 6e 20 28 77  65 6c 6c 20 69 74 20 77  |creen (well it w|
00000c00  69 6c 6c 20 64 6f 21 29  20 2a 2f 0a 63 68 61 72  |ill do!) */.char|
00000c10  20 2a 73 63 72 65 65 6e  5f 61 64 64 72 65 73 73  | *screen_address|
00000c20  5f 62 61 6e 6b 3b 20 2f  2a 20 74 68 69 73 20 69  |_bank; /* this i|
00000c30  73 20 61 6e 6f 74 68 65  72 20 70 6f 69 6e 74 65  |s another pointe|
00000c40  72 20 74 6f 20 74 68 65  20 6f 74 68 65 72 20 61  |r to the other a|
00000c50  72 65 61 20 6f 66 20 73  63 72 65 65 6e 20 6d 65  |rea of screen me|
00000c60  6d 6f 72 79 20 77 68 69  63 68 20 77 65 20 77 69  |mory which we wi|
00000c70  6c 6c 20 62 65 20 75 73  69 6e 67 20 66 6f 72 20  |ll be using for |
00000c80  53 43 52 45 45 4e 20 42  41 4e 4b 49 4e 47 20 2d  |SCREEN BANKING -|
00000c90  20 61 76 6f 69 64 69 6e  67 20 66 6c 69 63 6b 65  | avoiding flicke|
00000ca0  72 69 6e 67 20 6f 66 20  74 68 65 20 73 63 72 65  |ring of the scre|
00000cb0  65 6e 20 64 75 72 69 6e  67 20 61 6e 69 6d 61 74  |en during animat|
00000cc0  69 6e 67 20 67 72 61 70  68 69 63 73 20 2a 2f 0a  |ing graphics */.|
00000cd0  63 68 61 72 20 2a 73 63  72 65 65 6e 5f 61 64 64  |char *screen_add|
00000ce0  72 65 73 73 5f 74 65 6d  70 3b 20 2f 2a 20 74 68  |ress_temp; /* th|
00000cf0  69 73 20 69 73 20 61 20  73 70 61 72 65 20 70 6f  |is is a spare po|
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00000d30  6f 76 65 20 76 61 6c 75  65 73 20 2a 2f 0a 0a 2f  |ove values */../|
00000d40  2a 20 74 68 65 73 65 20  6e 65 77 20 46 49 58 45  |* these new FIXE|
00000d50  44 20 50 4f 49 4e 54 20  49 4e 54 45 47 45 52 20  |D POINT INTEGER |
00000d60  70 6f 69 6e 74 65 72 73  20 70 6f 69 6e 74 20 74  |pointers point t|
00000d70  6f 20 6c 6f 6f 6b 2d 75  70 20 74 61 62 6c 65 73  |o look-up tables|
00000d80  20 75 73 65 64 20 69 6e  20 74 68 65 20 72 61 79  | used in the ray|
00000d90  20 63 61 73 74 69 6e 67  20 65 6e 67 69 6e 65 2e  | casting engine.|
00000da0  20 54 68 65 73 65 20 61  72 65 20 65 78 70 6c 61  | These are expla|
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00000e00  61 6e 5f 74 61 62 6c 65  2c 2a 69 6e 76 5f 74 61  |an_table,*inv_ta|
00000e10  6e 5f 74 61 62 6c 65 3b  20 2f 2a 20 70 6f 69 6e  |n_table; /* poin|
00000e20  74 65 72 73 20 74 6f 20  74 61 6e 67 65 6e 74 20  |ters to tangent |
00000e30  6c 6f 6f 6b 5f 75 70 73  20 2a 2f 0a 69 6e 74 20  |look_ups */.int |
00000e40  2a 79 5f 73 74 65 70 2c  2a 78 5f 73 74 65 70 3b  |*y_step,*x_step;|
00000e50  20 20 20 20 20 20 20 20  20 20 20 2f 2a 20 70 6f  |           /* po|
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00000e70  6f 6d 70 6c 65 78 20 6c  6f 6f 6b 5f 75 70 73 20  |omplex look_ups |
00000e80  2a 2f 0a 69 6e 74 20 2a  69 6e 76 5f 63 6f 73 5f  |*/.int *inv_cos_|
00000e90  74 61 62 6c 65 2c 20 20  20 20 20 20 20 20 20 20  |table,          |
00000ea0  20 20 2f 2a 20 73 69 6e  2f 63 6f 73 20 74 61 62  |  /* sin/cos tab|
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00000ec0  20 20 2a 2f 0a 20 20 20  20 2a 69 6e 76 5f 73 69  |  */.    *inv_si|
00000ed0  6e 5f 74 61 62 6c 65 3b  0a 69 6e 74 20 2a 63 6f  |n_table;.int *co|
00000ee0  73 5f 74 61 62 6c 65 3b  20 20 20 20 20 20 20 20  |s_table;        |
00000ef0  20 20 20 20 20 20 20 20  2f 2a 20 63 6f 73 69 6e  |        /* cosin|
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00000f20  70 5f 74 61 62 6c 65 3b  20 20 20 20 20 20 20 20  |p_table;        |
00000f30  20 20 20 20 20 20 2f 2a  20 72 65 63 69 70 72 6f  |      /* recipro|
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00000f80  6c 65 2c 20 20 20 20 20  20 20 20 20 20 20 20 20  |le,             |
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00000fd0  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 2f  |               /|
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00001000  20 20 2f 2a 20 75 73 65  64 20 74 6f 20 73 74 6f  |  /* used to sto|
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00001030  0a 2f 2a 20 46 55 4e 43  54 49 4f 4e 20 64 65 66  |./* FUNCTION def|
00001040  69 6e 69 74 69 6f 6e 73  20 2a 2f 0a 0a 2f 2a 20  |initions */../* |
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00001130  20 61 6e 67 74 3b 20 2f  2a 20 73 61 6d 65 20 2a  | angt; /* same *|
00001140  2f 0a 0a 66 6c 6f 61 74  20 72 61 64 5f 61 6e 67  |/..float rad_ang|
00001150  6c 65 3b 20 2f 2a 20 74  68 69 73 20 68 6f 6c 64  |le; /* this hold|
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00001170  75 69 76 61 6c 65 6e 74  20 6f 66 20 74 68 65 20  |uivalent of the |
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000011b0  20 3d 20 30 2d 36 2e 77  68 61 74 65 76 65 72 20  | = 0-6.whatever |
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00001200  31 38 30 30 20 69 6e 73  74 65 61 64 20 6f 66 20  |1800 instead of |
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00001280  72 61 6d 65 20 72 61 74  65 2e 20 59 65 73 21 20  |rame rate. Yes! |
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000012d0  0a 74 61 6e 5f 74 61 62  6c 65 20 20 20 20 20 3d  |.tan_table     =|
000012e0  20 28 69 6e 74 20 2a 29  6d 61 6c 6c 6f 63 28 73  | (int *)malloc(s|
000012f0  69 7a 65 6f 66 28 69 6e  74 29 20 2a 20 28 41 4e  |izeof(int) * (AN|
00001300  47 4c 45 5f 33 36 30 2b  31 29 29 3b 0a 69 6e 76  |GLE_360+1));.inv|
00001310  5f 74 61 6e 5f 74 61 62  6c 65 20 3d 20 28 69 6e  |_tan_table = (in|
00001320  74 20 2a 29 6d 61 6c 6c  6f 63 28 73 69 7a 65 6f  |t *)malloc(sizeo|
00001330  66 28 69 6e 74 29 20 2a  20 28 41 4e 47 4c 45 5f  |f(int) * (ANGLE_|
00001340  33 36 30 2b 31 29 29 3b  0a 0a 79 5f 73 74 65 70  |360+1));..y_step|
00001350  20 20 20 20 20 20 20 20  3d 20 28 69 6e 74 20 2a  |        = (int *|
00001360  29 6d 61 6c 6c 6f 63 28  73 69 7a 65 6f 66 28 69  |)malloc(sizeof(i|
00001370  6e 74 29 20 2a 20 28 41  4e 47 4c 45 5f 33 36 30  |nt) * (ANGLE_360|
00001380  2b 31 29 29 3b 0a 78 5f  73 74 65 70 20 20 20 20  |+1));.x_step    |
00001390  20 20 20 20 3d 20 28 69  6e 74 20 20 2a 29 6d 61  |    = (int  *)ma|
000013a0  6c 6c 6f 63 28 73 69 7a  65 6f 66 28 69 6e 74 29  |lloc(sizeof(int)|
000013b0  20 2a 20 28 41 4e 47 4c  45 5f 33 36 30 2b 31 29  | * (ANGLE_360+1)|
000013c0  29 3b 0a 0a 63 6f 73 5f  74 61 62 6c 65 20 20 20  |);..cos_table   |
000013d0  20 20 3d 20 28 69 6e 74  20 20 2a 29 6d 61 6c 6c  |  = (int  *)mall|
000013e0  6f 63 28 73 69 7a 65 6f  66 28 69 6e 74 29 20 2a  |oc(sizeof(int) *|
000013f0  20 28 41 4e 47 4c 45 5f  33 36 30 2b 31 29 29 3b  | (ANGLE_360+1));|
00001400  0a 69 6e 76 5f 63 6f 73  5f 74 61 62 6c 65 20 3d  |.inv_cos_table =|
00001410  20 28 69 6e 74 20 20 2a  29 6d 61 6c 6c 6f 63 28  | (int  *)malloc(|
00001420  73 69 7a 65 6f 66 28 69  6e 74 29 20 2a 20 28 41  |sizeof(int) * (A|
00001430  4e 47 4c 45 5f 33 36 30  2b 31 29 29 3b 0a 69 6e  |NGLE_360+1));.in|
00001440  76 5f 73 69 6e 5f 74 61  62 6c 65 20 3d 20 28 69  |v_sin_table = (i|
00001450  6e 74 20 20 2a 29 6d 61  6c 6c 6f 63 28 73 69 7a  |nt  *)malloc(siz|
00001460  65 6f 66 28 69 6e 74 29  20 2a 20 28 41 4e 47 4c  |eof(int) * (ANGL|
00001470  45 5f 33 36 30 2b 31 29  29 3b 0a 2f 2a 20 6e 65  |E_360+1));./* ne|
00001480  77 20 74 61 62 6c 65 2c  20 66 6f 72 20 74 68 65  |w table, for the|
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000014a0  64 20 75 73 69 6e 67 20  61 20 64 69 76 69 64 65  |d using a divide|
000014b0  20 2a 2f 0a 72 65 63 69  70 5f 74 61 62 6c 65 20  | */.recip_table |
000014c0  20 20 3d 20 28 69 6e 74  20 20 2a 29 6d 61 6c 6c  |  = (int  *)mall|
000014d0  6f 63 28 73 69 7a 65 6f  66 28 69 6e 74 29 20 2a  |oc(sizeof(int) *|
000014e0  20 28 4d 41 58 5f 44 49  53 54 41 4e 43 45 2b 31  | (MAX_DISTANCE+1|
000014f0  29 29 3b 0a 2f 2a 20 6e  65 77 20 74 61 62 6c 65  |));./* new table|
00001500  73 20 66 6f 72 20 6d 6f  76 69 6e 67 20 74 68 65  |s for moving the|
00001510  20 76 69 65 77 20 70 6f  69 6e 74 20 2a 2f 0a 64  | view point */.d|
00001520  78 5f 74 61 62 6c 65 20  20 20 20 20 20 3d 20 28  |x_table      = (|
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00001540  7a 65 6f 66 28 69 6e 74  29 20 2a 20 28 41 4e 47  |zeof(int) * (ANG|
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00007910  69 66 28 77 6f 72 6c 64  5b 76 69 65 77 5f 79 3e  |if(world[view_y>|
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00007930  7b 0a 20 20 70 72 69 6e  74 66 28 22 42 61 64 20  |{.  printf("Bad |
00007940  63 6f 6f 72 64 69 6e 61  74 65 73 20 67 69 76 65  |coordinates give|
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00007980  0a 7d 0a 0a 2f 2a 20 6e  6f 77 20 77 65 20 63 61  |.}../* now we ca|
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00007af0  70 72 69 6e 74 66 28 22  53 77 69 74 63 68 69 6e  |printf("Switchin|
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