Home » Archimedes archive » Acorn User » AU 1997-06 B.adf » Features » 3D/!AUA_Ray/source/c/engine
3D/!AUA_Ray/source/c/engine
This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.
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| Tape/disk: | Home » Archimedes archive » Acorn User » AU 1997-06 B.adf » Features |
| Filename: | 3D/!AUA_Ray/source/c/engine |
| Read OK: | ✔ |
| File size: | 8716 bytes |
| Load address: | 0000 |
| Exec address: | 0000 |
File contents
/*
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 SCREEN_WIDTH 320 /* This is the width of the mode 13 screen */
#define SCREEN_HEIGHT 256 /* This is the height of the mode 13 screen */
#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 */
/* these next defines represent a new fixed point form of angle-counting. Basically this system is used to avoid using floating point radian angles, which (especially on an Acorn) take a long time. It also makes look-up table referencing a lot easier, as the index has to be an integer anyway! */
#define ANGLE_0 0
#define ANGLE_6 30
#define ANGLE_30 160
#define ANGLE_45 240
#define ANGLE_60 320
#define ANGLE_90 480
#define ANGLE_180 960
#define ANGLE_225 1200
#define ANGLE_270 1440
#define ANGLE_360 1920
/* GLOBAL variables */
char world[WORLD_HEIGHT+1][WORLD_WIDTH+1];/* This holds our text data file */
char walls[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 9 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 */
/* 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)(13312/(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[8]; /* this is used to pass variables to a super fast sliver render */
/* 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[1]=(char *)walls;
variables[5]=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=319; 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=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)
{
/* 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;
}
else
{
/* 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)
{
/* 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;
}
else
{
/* 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[2]=(yi_save & 0x003f); /* this works out the column of the wall to be plotted (0-64), by calculating where abouts in the cell the intersection was, covered in the article. Note the optimization of yi_save % 64 */
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[6]=x_hit_type; /* finally we store the wall number to plot */
/* 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[2]=(xi_save & 0x003f); /*notice that we use xi instead of yi_save*/
variables[3]=scale-1;
variables[4]=ray;
/* 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! */
variables[6]=y_hit_type+1;
/* call our sliver engine */
ourlib_sliver(&variables[0]);
}
/* 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 */
}
/* 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! */
for(wall_number=1,y=0;y<SCREEN_HEIGHT;y+=WALL_HEIGHT)for(x=0;x<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;
}
}
/* 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';
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);
}
/* NEWER MAIN function .
This function now incorporates the following (see article)
FIXED POINT LOOK-UPS for MOVEMENT of viewpoint!
SCREEN BANKING to avoid flicker!
COLOURED FLOOR AND CEILINGS!
All changes are commented */
void main(void)
{
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! */
int temporary_variables[10]; /* this array can be used to pass parameters */
/* we'll assign those now, for clearing the screen (slowly) */
temporary_variables[1]=temporary_variables[2]=temporary_variables[5]=0;
temporary_variables[3]=320;temporary_variables[4]=256;
/* first, we need the user to input values for view_x,view_y and view_angle*/
printf("******* NEW, IMPROVED RAY CASTER *******\nThis month's ray caster involves SCREENBANKING, COLOURED FLOORS AND CEILINGS, FIXED POINT MATHS and MORE. It still runs at full screen, but next month will have an adjustable screen size to run much quicker. Next month's will go atleast 25 fps on a RPC 600. An assembler version is a possibility.\nPlease enter starting values for View_X, View_Y, Viewing angle. Make sure the view doesn't start in a wall!\n Use the cursor keys to move and Q to quit\n\n");
scanf("%d %d %d",&view_x,&view_y,&view_angle);
/* confirm this is ok */
printf("You entered %d %d and %d Press 0 to quit and re-enter or any other number to continue...\n",view_x,view_y,view_angle);
scanf("%d",&key_press);
/* if q is pressed then exit, else continue */
if(!key_press)exit(1);
/* 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();
/* 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);
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();
/* we shall clear the screen here */
temporary_variables[0]=screen_address_bank;
ourlib_colour_box(temporary_variables);
/* 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. In LATER VERSIONS of the engine these sort of details will be called through the COMMAND LINE, so no source code changing will be necessary */
ourlib_setup_background(148,25);
/* 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 */
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;
x_cell = view_x/CELL_X_SIZE;
y_cell = view_y/CELL_Y_SIZE;
x_sub_cell = view_x % CELL_X_SIZE;
y_sub_cell = view_y % CELL_Y_SIZE;
/* 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);
}
}
/* 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\n\nNote that this program should be slow even on a RISC PC. Next month will include variable screen sizes so the program is a lot faster. Don't panic!\n\n",(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,|
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00000090 20 61 74 20 74 68 65 0a 20 20 20 6f 77 6e 65 72 | at the. owner|
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000000b0 6e 20 55 73 65 72 20 6f 72 20 74 68 65 20 61 75 |n User or the au|
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000000f0 0a 2f 2a 20 41 55 54 48 4f 52 53 20 4e 4f 54 45 |./* AUTHORS NOTE|
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00000210 69 6c 6c 20 70 61 73 73 20 69 74 20 6f 6e 2e 20 |ill pass it on. |
00000220 54 68 61 6e 6b 20 79 6f 75 2e 20 2a 2f 0a 0a 2f |Thank you. */../|
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00008600 72 20 69 6e 66 6f 2e 20 2a 2f 0a 70 72 69 6e 74 |r info. */.print|
00008610 66 28 22 2a 2a 2a 2a 2a 2a 2a 20 46 52 41 4d 45 |f("******* FRAME|
00008620 53 20 50 45 52 20 53 45 43 4f 4e 44 20 2a 2a 2a |S PER SECOND ***|
00008630 2a 2a 2a 2a 2a 5c 6e 20 20 20 20 20 20 20 25 66 |*****\n %f|
00008640 5c 6e 5c 6e 4e 6f 74 65 20 74 68 61 74 20 74 68 |\n\nNote that th|
00008650 69 73 20 70 72 6f 67 72 61 6d 20 73 68 6f 75 6c |is program shoul|
00008660 64 20 62 65 20 73 6c 6f 77 20 65 76 65 6e 20 6f |d be slow even o|
00008670 6e 20 61 20 52 49 53 43 20 50 43 2e 20 4e 65 78 |n a RISC PC. Nex|
00008680 74 20 6d 6f 6e 74 68 20 77 69 6c 6c 20 69 6e 63 |t month will inc|
00008690 6c 75 64 65 20 76 61 72 69 61 62 6c 65 20 73 63 |lude variable sc|
000086a0 72 65 65 6e 20 73 69 7a 65 73 20 73 6f 20 74 68 |reen sizes so th|
000086b0 65 20 70 72 6f 67 72 61 6d 20 69 73 20 61 20 6c |e program is a l|
000086c0 6f 74 20 66 61 73 74 65 72 2e 20 44 6f 6e 27 74 |ot faster. Don't|
000086d0 20 70 61 6e 69 63 21 5c 6e 5c 6e 22 2c 28 66 6c | panic!\n\n",(fl|
000086e0 6f 61 74 29 66 72 61 6d 65 73 2f 28 66 6c 6f 61 |oat)frames/(floa|
000086f0 74 29 28 28 74 69 6d 65 5f 66 69 6e 69 73 68 2d |t)((time_finish-|
00008700 74 69 6d 65 5f 73 74 61 72 74 29 2f 31 30 30 29 |time_start)/100)|
00008710 29 3b 0a 7d 0a 0a |);.}..|
00008716 
.