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raycast.c
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raycast.c
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#include <math.h>
#include <fixmath.h>
#include <c64/vic.h>
#include <c64/asm6502.h>
#include "raycast.h"
#include "maze.h"
#include "display.h"
//static int sintab[64], costab[64];
//static int dsintab[64], dcostab[64];
#pragma data(tables)
// Table of 8.8 sine for 64 parts of a circle
const int sintab[64] = {
0, 25, 50, 74, 98, 121, 142, 162, 181, 198, 213, 226, 237, 245, 251, 255, 256, 255, 251, 245, 237, 226, 213, 198, 181, 162, 142, 121, 98, 74, 50, 25, 0, -25, -50, -74, -98, -121, -142, -162, -181, -198, -213, -226, -237, -245, -251, -255, -256, -255, -251, -245, -237, -226, -213, -198, -181, -162, -142, -121, -98, -74, -50, -25
};
// Table of 8.8 cosine for 64 parts of a circle
const int costab[64] = {
256, 255, 251, 245, 237, 226, 213, 198, 181, 162, 142, 121, 98, 74, 50, 25, 0, -25, -50, -74, -98, -121, -142, -162, -181, -198, -213, -226, -237, -245, -251, -255, -256, -255, -251, -245, -237, -226, -213, -198, -181, -162, -142, -121, -98, -74, -50, -25, 0, 25, 50, 74, 98, 121, 142, 162, 181, 198, 213, 226, 237, 245, 251, 255
};
// Table of scaled 8.8 sine for 64 parts of a circle for one column
const int dsintab[64] = {
0, -1, -2, -4, -5, -6, -7, -8, -9, -10, -11, -11, -12, -12, -13, -13, -13, -13, -13, -12, -12, -11, -11, -10, -9, -8, -7, -6, -5, -4, -2, -1, 0, 1, 2, 4, 5, 6, 7, 8, 9, 10, 11, 11, 12, 12, 13, 13, 13, 13, 13, 12, 12, 11, 11, 10, 9, 8, 7, 6, 5, 4, 2, 1
};
// Table of scaled 8.8 cosine for 64 parts of a circle for one column
const int dcostab[64] = {
13, 13, 13, 12, 12, 11, 11, 10, 9, 8, 7, 6, 5, 4, 2, 1, 0, -1, -2, -4, -5, -6, -7, -8, -9, -10, -11, -11, -12, -12, -13, -13, -13, -13, -13, -12, -12, -11, -11, -10, -9, -8, -7, -6, -5, -4, -2, -1, 0, 1, 2, 4, 5, 6, 7, 8, 9, 10, 11, 11, 12, 12, 13, 13
};
#pragma data(data)
// Static table of quotients 4096 / i clamped at 255
char inverse[4096] = {
255,
#assign i 1
#repeat
(4096 / i > 255) ? 255 : 4096 / i,
#assign i i + 1
#until i == 4096
#undef i
};
#pragma align(inverse, 256)
// Table of LSB and MSB of squares for fast 8 by 8 multiply
#pragma bss(dyntables)
char sqrtabl[256], sqrtabh[256];
#pragma align(sqrtabl, 256)
#pragma align(sqrtabh, 256)
char blut[136];
// Result of ray cast of full screen for each column
static char col_h[41], col_x[41], col_y[41], col_d[41];
#pragma bss(bss)
// Color lookup for maze block and direction
char clut[4 * 8] = {
0x00, 0x00, 0x00, 0x00, // MF_EMPTY
0x30, 0x30, 0x30, 0x30, // MF_EXIT
0xf0, 0xe0, 0xf0, 0xe0, // MF_MINE
0x00, 0x00, 0x00, 0x00, // MF_DUMMY
0x40, 0x50, 0x60, 0x50, // MF_RED
0x70, 0x80, 0x90, 0x80, // MF_BLUE
0xa0, 0xb0, 0xc0, 0xb0, // BF_PURPLE
0xd0, 0xe0, 0xf0, 0xe0, // MF_WHITE
};
void rcast_init_tables(void)
{
#if 0
for(int i=0; i<64; i++)
{
float f = 256 * sin(i * (PI / 32));
int j = (i + 48) & 63;
sintab[i] = f;
costab[j] = f;
dsintab[i] = - f * 0.05;
dcostab[j] = f * 0.05;
vic.color_border++;
}
#endif
// Init table of squares
for(unsigned i=0; i<256; i++)
{
unsigned s = i * i;
sqrtabl[i] = s & 0xff;
sqrtabh[i] = s >> 8;
// vic.color_border++;
}
for(int i=0; i<136; i++)
{
int t = 72 / (i + 8);
if (t > 6) t = 6;
blut[i] = 16 * (6 - t);
}
}
// Stub to call a fastcode function to fill a column with a given height and color
static void drawColumn(char col, char height, char color)
{
__asm
{
ldx col
// MSB address of function is based on height of column in chars
lda height
lsr
lsr
lsr
ora #$e0
sta jp + 2
// LSB is based on double buffer screen address
lda sindex
sta jp + 1
// Select bottom char based on height, replace the non exiting
// zero height char with the shared one
lda height
and #7
bne w1
ldy #2
bne w2
w1:
ora color
tay
w2:
// Select top char based on height / 2
lda height
lsr
and #7
ora #8
ora color
// Call fastcode
jp:
jmp $e000
}
}
void rcast_init_fastcode(void)
{
// Two sets of fastcode for the double buffering
for(int s=0; s<2; s++)
{
// Top left screen coordinate
unsigned sp = (unsigned)Screen + 0x0400 * s;
// Column heights in chars can range from 0 to 16, top section is half height
for(int i=0; i<=16; i++)
{
// Start address of fastcode routine
char * dp = (char *)0xe000 + 256 * i + 128 * s;
// Start position of filled section
char yl = 8 - (i >> 1);
// Height of bottom section
char yh = 8 + i;
// Offset into fastcode
char di = 0;
// Check if top partial filled char is visible
if (yl > 0)
{
// Write top char
unsigned fp = sp + 40 * (yl - 1);
di += asm_ax(dp + di, ASM_STA, fp);
}
// Check if there are inner chars to fill
if (yl < yh)
{
// Load inner char for color, by masking out bits from top char
di += asm_im(dp + di, ASM_AND, 0xf0);
// Add stores to fill the inner range
for(char j=yl; j<yh; j++)
{
unsigned fp = sp + 40 * j;
di += asm_ax(dp + di, ASM_STA, fp);
}
}
// Is there space for the partial filled bottom char
if (yh < 25)
{
// Draw bottom char
di += asm_np(dp + di, ASM_TYA);
unsigned fp = sp + 40 * yh;
di += asm_ax(dp + di, ASM_STA, fp);
}
// Load empty char
di += asm_im(dp + di, ASM_LDA, 0x00);
// Fill empty top region
for(char j=0; j<yl - 1; j++)
{
unsigned fp =sp + 40 * j;
di += asm_ax(dp + di, ASM_STA, fp);
}
// Load checkerd bottom char
di += asm_im(dp + di, ASM_LDA, 0x03);
// Fill floor region
for(char j=yh + 1; j<25; j++)
{
unsigned fp = sp + 40 * j;
di += asm_ax(dp + di, ASM_STA, fp);
}
// And done
di += asm_np(dp + di, ASM_RTS);
}
}
}
// Square of two unsigned bytes using table lookup
static inline unsigned square(char c)
{
return (unsigned)sqrtabl[c] | ((unsigned)sqrtabh[c] << 8);
}
// Multiply two eight bit numbers using binomials (a + b)^2 = a^2 + 2ab + b^2
static inline unsigned mul88(char a, char b)
{
unsigned s = a + b;
if (s >= 256)
{
s &= 0xff;
return ((square(s) - square(a) - square(b)) >> 1) + (s << 8);
}
else
return (square(s) - square(a) - square(b)) >> 1;
}
// Calculate height of a column with given distance r and scale d
static inline char colheight(unsigned d, unsigned r)
{
if (r >= 4096)
return 0;
else
{
unsigned h = mul88(d, inverse[r]) >> 4;
if (h >= 256)
return 255;
else
return h;
}
}
// Cast a single ray with unsigned fractionals
// sx : column on screen
// ix : x position in blocks in maze
// iy : y position in blocks in maze
// irx : distance in x direction to wall in 8.8
// iry : distacne in y direction to wall in 8.8
// dix : direction in x (+1, 0, -1)
// diy : direction in y (+1 ,0, -1)
// idx : fractional move in x direction
// idy : fractional move in y direction
static inline void dcast(char sx, char ix, char iy, unsigned irx, unsigned iry, signed char dix, signed char diy, unsigned idx, unsigned idy)
{
// Start position in maze
const char * bp = maze_grid + 256 * iy;
// Sacrifice some bits of directional precision to fit into a signed byte
char udx = idx >> 2, udy = idy >> 2;
// Calculate start fraction
signed char id = (int)(mul88(irx, udy) - mul88(iry, udx)) >> 8;
for(;;)
{
// Loop while next x block is closer in ray direction
while (id < 0)
{
// Advance in x direction
ix += dix;
// Check if filled block reached
if (bp[ix])
{
// Remember block and distance
col_x[sx] = ix;
col_y[sx] = (char)((unsigned)bp >> 8);
col_d[sx] = dix < 0 ? bp[ix] | 0 : bp[ix] | 2;
col_h[sx] = colheight(udx, irx);
return;
}
// Increase distance in x by one block
irx += 256;
// Update fraction
id += udy;
}
// Loop while next y block is closer in ray direction
while (id >= 0)
{
// Advance in y direction
bp += 256 * diy;
// Check if filled block reached
if (bp[ix])
{
// Remember block and distance
col_x[sx] = ix;
col_y[sx] = (char)((unsigned)bp >> 8);
col_d[sx] = diy < 0 ? bp[ix] | 1 : bp[ix] | 3;
col_h[sx] = colheight(udy, iry);
return;
}
// Increase distance in y by one block
iry += 256;
// Update fraction
id -= udx;
}
}
}
void rcast_draw_screen(void)
{
// For each column
for(char x=0; x<40; x++)
{
// Get height of column
char w = col_h[x];
// Clip
if (w > 135)
w = 135;
// Call fastcode to fill
drawColumn(x, w, clut[col_d[x]]);
}
}
// Cast a single ray with signed fractionals
// sx : column on screen
// ipx : x position in maze in 8.8
// ipy : y position in maze in 8.8
// idx : x component of ray in 8.8
// idy : y component of ray in 8.8
inline void icast(char sx, int ipx, int ipy, int idx, int idy)
{
// Get integer portion of position
char ix = ipx >> 8, iy = ipy >> 8;
// Unsigned fractional portion of position
unsigned irx = ipx & 255;
unsigned iry = ipy & 255;
// Expand inline code of dcast for each possible sign combination of
// ray direction
if (idx < 0)
{
if (idy < 0)
{
dcast(sx, ix, iy, irx, iry, -1, -1, -idx, -idy);
}
else
{
dcast(sx, ix, iy, irx, iry ^ 0xff, -1, 1, -idx, idy);
}
}
else
{
if (idy < 0)
{
dcast(sx, ix, iy, irx ^ 0xff, iry, 1, -1, idx, -idy);
}
else
{
dcast(sx, ix, iy, irx ^ 0xff, iry ^ 0xff, 1, 1, idx, idy);
}
}
}
void rcast_cast_rays(int ipx, int ipy, int idx, int idy, int iddx, int iddy)
{
// Let mine flicker
clut[MF_MINE + 0] ^= 0x10;
clut[MF_MINE + 1] ^= 0x10;
clut[MF_MINE + 2] ^= 0x10;
clut[MF_MINE + 3] ^= 0x10;
// Cast left most ray
icast(0, ipx, ipy, idx, idy);
// Step through all columns in a step size of two
for(int i=0; i<39; i+=2)
{
// Cast ray
icast(i + 2, ipx, ipy, idx + 2 * iddx, idy + 2 * iddy);
// Check if this is the same block as the one of the previous
// column (two to the left)
if (col_x[i] == col_x[i + 2] && col_y[i] == col_y[i + 2] && col_d[i] == col_d[i + 2])
{
// If so, just interpolate the column inbetween
col_x[i + 1] = col_x[i];
col_y[i + 1] = col_y[i];
col_d[i + 1] = col_d[i];
col_h[i + 1] = (col_h[i] + col_h[i + 2]) >> 1;
}
else
{
// Cast ray for column inbetween
icast(i + 1, ipx, ipy, idx + iddx, idy + iddy);
}
// Next column
idx += 2 * iddx;
idy += 2 * iddy;
}
}