আমি জিমির প্রস্তাবিত অ্যালগরিদম বাস্তবায়ন করেছি।
কোডটিতে কর্মের ভিডিও এখানে: https://youtu.be/lIlPfwlcbHo
/*
What this code does:
Rasterizes a single Field Of View octant on a grid, similar to the way
FOV / shadowcasting is implemented in some roguelikes.
Clips to bitmap
Steps on pixel centers
Optional attenuation
Optional circle clip
Optional lit blocking tiles
To rasterize the entire FOV, call this in a loop with octant in range 0-7
Inspired by http://blogs.msdn.com/b/ericlippert/archive/2011/12/12/shadowcasting-in-c-part-one.aspx
*/
static inline int Mini( int a, int b ) {
return a < b ? a : b;
}
static inline int Maxi( int a, int b ) {
return a > b ? a : b;
}
static inline int Clampi( int v, int min, int max ) {
return Maxi( min, Mini( v, max ) );
}
typedef union c2_s {
struct {
int x, y;
};
int a[2];
} c2_t;
static const c2_t c2zero = { .a = { 0, 0 } };
static const c2_t c2one = { .a = { 1, 1 } };
static inline c2_t c2xy( int x, int y ) {
c2_t c = { { x, y } };
return c;
}
static inline c2_t c2Neg( c2_t c ) {
return c2xy( -c.x, -c.y );
}
static inline c2_t c2Add( c2_t a, c2_t b ) {
return c2xy( a.x + b.x, a.y + b.y );
}
static inline c2_t c2Sub( c2_t a, c2_t b ) {
return c2xy( a.x - b.x, a.y - b.y );
}
static inline int c2Dot( c2_t a, c2_t b ) {
return a.x * b.x + a.y * b.y;
}
static inline int c2CrossC( c2_t a, c2_t b ) {
return a.x * b.y - a.y * b.x;
}
static inline c2_t c2Clamp( c2_t c, c2_t min, c2_t max ) {
return c2xy( Clampi( c.x, min.x, max.x ), Clampi( c.y, min.y, max.y ) );
}
static inline c2_t c2Scale( c2_t a, int s ) {
return c2xy( a.x * s, a.y * s );
}
void RasterizeFOVOctant( int originX, int originY,
int radius,
int bitmapWidth, int bitmapHeight,
int octant,
int skipAttenuation,
int skipClampToRadius,
int darkWalls,
const unsigned char *inBitmap,
unsigned char *outBitmap ) {
#define READ_PIXEL(c) inBitmap[(c).x+(c).y*bitmapWidth]
#define WRITE_PIXEL(c,color) outBitmap[(c).x+(c).y*bitmapWidth]=(color)
#define MAX_RAYS 64
#define ADD_RAY(c) {nextRays->rays[Mini(nextRays->numRays,MAX_RAYS-1)] = (c);nextRays->numRays++;}
#define IS_ON_MAP(c) ((c).x >= 0 && (c).x < bitmapWidth && (c).y >= 0 && (c).y < bitmapHeight)
typedef struct {
int numRays;
c2_t rays[MAX_RAYS];
} raysList_t;
// keep these coupled like this
static const const c2_t bases[] = {
{ { 1, 0 } }, { { 0, 1 } },
{ { 1, 0 } }, { { 0, -1 } },
{ { -1, 0 } }, { { 0, -1 } },
{ { -1, 0 } }, { { 0, 1 } },
{ { 0, 1 } }, { { -1, 0 } },
{ { 0, 1 } }, { { 1, 0 } },
{ { 0, -1 } }, { { 1, 0 } },
{ { 0, -1 } }, { { -1, 0 } },
};
c2_t e0 = bases[( octant * 2 + 0 ) & 15];
c2_t e1 = bases[( octant * 2 + 1 ) & 15];
raysList_t rayLists[2] = { {
.numRays = 2,
.rays = {
c2xy( 1, 0 ),
c2xy( 1, 1 ),
},
} };
c2_t bitmapSize = c2xy( bitmapWidth, bitmapHeight );
c2_t bitmapMax = c2Sub( bitmapSize, c2one );
c2_t origin = c2Clamp( c2xy( originX, originY ), c2zero, bitmapMax );
if ( READ_PIXEL( origin ) ) {
WRITE_PIXEL( origin, 255 );
return;
}
c2_t dmin = c2Neg( origin );
c2_t dmax = c2Sub( bitmapMax, origin );
int dmin0 = c2Dot( dmin, e0 );
int dmax0 = c2Dot( dmax, e0 );
int limit0 = Mini( radius, dmin0 > 0 ? dmin0 : dmax0 );
int dmin1 = c2Dot( dmin, e1 );
int dmax1 = c2Dot( dmax, e1 );
int limit1 = Mini( radius, dmin1 > 0 ? dmin1 : dmax1 );
c2_t ci = origin;
for ( int i = 0; i <= limit0; i++ ) {
int i2 = i * 2;
raysList_t *currRays = &rayLists[( i + 0 ) & 1];
raysList_t *nextRays = &rayLists[( i + 1 ) & 1];
nextRays->numRays = 0;
for ( int r = 0; r < currRays->numRays - 1; r += 2 ) {
c2_t r0 = currRays->rays[r + 0];
c2_t r1 = currRays->rays[r + 1];
int inyr0 = ( i2 - 1 ) * r0.y / r0.x;
int outyr0 = ( i2 + 1 ) * r0.y / r0.x;
int inyr1 = ( i2 - 1 ) * r1.y / r1.x;
int outyr1 = ( i2 + 1 ) * r1.y / r1.x;
// every pixel with a center INSIDE the frustum is lit
int starty = outyr0 + 1;
if ( c2CrossC( r0, c2xy( i2, outyr0 ) ) < 0 ) {
starty++;
}
starty /= 2;
c2_t start = c2Add( ci, c2Scale( e1, starty ) );
int endy = inyr1 + 1;
if ( c2CrossC( r1, c2xy( i2, inyr1 + 1 ) ) > 0 ) {
endy--;
}
endy /= 2;
//c2_t end = c2Add( ci, c2Scale( e1, endy ) );
{
int y;
c2_t p;
int miny = starty;
int maxy = Mini( endy, limit1 );
for ( y = miny, p = start; y <= maxy; y++, p = c2Add( p, e1 ) ) {
WRITE_PIXEL( p, 255 );
}
}
// push rays for the next column
// correct the bounds first
c2_t bounds0;
c2_t bounds1;
c2_t firstin = c2Add( ci, c2Scale( e1, ( inyr0 + 1 ) / 2 ) );
c2_t firstout = c2Add( ci, c2Scale( e1, ( outyr0 + 1 ) / 2 ) );
if ( ( IS_ON_MAP( firstin ) && ! READ_PIXEL( firstin ) )
&& ( IS_ON_MAP( firstout ) && ! READ_PIXEL( firstout ) ) ) {
bounds0 = r0;
} else {
int top = ( outyr0 + 1 ) / 2;
int bottom = Mini( ( inyr1 + 1 ) / 2, limit1 );
int y;
c2_t p = c2Add( ci, c2Scale( e1, top ) );
for ( y = top * 2; y <= bottom * 2; y += 2, p = c2Add( p, e1 ) ) {
if ( ! READ_PIXEL( p ) ) {
break;
}
// pixels that force ray corrections are lit too
WRITE_PIXEL( p, 255 );
}
bounds0 = c2xy( i2 - 1, y - 1 );
inyr0 = ( i2 - 1 ) * bounds0.y / bounds0.x;
outyr0 = ( i2 + 1 ) * bounds0.y / bounds0.x;
}
c2_t lastin = c2Add( ci, c2Scale( e1, ( inyr1 + 1 ) / 2 ) );
c2_t lastout = c2Add( ci, c2Scale( e1, ( outyr1 + 1 ) / 2 ) );
if ( ( IS_ON_MAP( lastin ) && ! READ_PIXEL( lastin ) )
&& ( IS_ON_MAP( lastout ) && ! READ_PIXEL( lastout ) ) ) {
bounds1 = r1;
} else {
int top = ( outyr0 + 1 ) / 2;
int bottom = Mini( ( inyr1 + 1 ) / 2, limit1 );
int y;
c2_t p = c2Add( ci, c2Scale( e1, bottom ) );
for ( y = bottom * 2; y >= top * 2; y -= 2, p = c2Sub( p, e1 ) ) {
if ( ! READ_PIXEL( p ) ) {
break;
}
// pixels that force ray corrections are lit too
WRITE_PIXEL( p, 255 );
}
bounds1 = c2xy( i2 + 1, y + 1 );
inyr1 = ( i2 - 1 ) * bounds1.y / bounds1.x;
outyr1 = ( i2 + 1 ) * bounds1.y / bounds1.x;
}
// closed frustum - quit
if ( c2CrossC( bounds0, bounds1 ) <= 0 ) {
continue;
}
// push actual rays
{
ADD_RAY( bounds0 );
int top = ( outyr0 + 1 ) / 2;
int bottom = Mini( ( inyr1 + 1 ) / 2, limit1 );
c2_t p = c2Add( ci, c2Scale( e1, top ) );
int prevPixel = READ_PIXEL( p );
for ( int y = top * 2; y <= bottom * 2; y += 2, p = c2Add( p, e1 ) ) {
int pixel = READ_PIXEL( p );
if ( prevPixel != pixel ) {
c2_t ray;
if ( pixel ) {
ray = c2xy( i2 + 1, y - 1 );
} else {
ray = c2xy( i2 - 1, y - 1 );
}
ADD_RAY( ray );
}
prevPixel = pixel;
}
ADD_RAY( bounds1 );
}
}
ci = c2Add( ci, e0 );
}
if ( ! skipAttenuation ) {
c2_t ci = origin;
int rsq = radius * radius;
for ( int i = 0; i <= limit0; i++ ) {
c2_t p = ci;
for ( int j = 0; j <= limit1; j++ ) {
c2_t d = c2Sub( p, origin );
int dsq = c2Dot( d, d );
int mod = 255 - Mini( dsq * 255 / rsq, 255 );
int lit = !! outBitmap[p.x + p.y * bitmapWidth];
WRITE_PIXEL( p, mod * lit );
p = c2Add( p, e1 );
}
ci = c2Add( ci, e0 );
}
} else if ( ! skipClampToRadius ) {
c2_t ci = origin;
int rsq = radius * radius;
for ( int i = 0; i <= limit0; i++ ) {
c2_t p = ci;
for ( int j = 0; j <= limit1; j++ ) {
c2_t d = c2Sub( p, origin );
if ( c2Dot( d, d ) > rsq ) {
WRITE_PIXEL( p, 0 );
}
p = c2Add( p, e1 );
}
ci = c2Add( ci, e0 );
}
}
if ( darkWalls ) {
c2_t ci = origin;
for ( int i = 0; i <= limit0; i++ ) {
c2_t p = ci;
for ( int j = 0; j <= limit1; j++ ) {
if ( READ_PIXEL( p ) ) {
WRITE_PIXEL( p, 0 );
}
p = c2Add( p, e1 );
}
ci = c2Add( ci, e0 );
}
}
}