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crt_nes.c
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crt_nes.c
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/*****************************************************************************/
/*
* NTSC/CRT - integer-only NTSC video signal encoding / decoding emulation
*
* by EMMIR 2018-2023
* modifications for Mesen by Persune
* https://github.com/LMP88959/NTSC-CRT
*
* YouTube: https://www.youtube.com/@EMMIR_KC/videos
* Discord: https://discord.com/invite/hdYctSmyQJ
*/
/*****************************************************************************/
#include "crt_core.h"
#if (CRT_SYSTEM == CRT_SYSTEM_NES)
#include <stdlib.h>
#include <string.h>
/* generate the square wave for a given 9-bit pixel and phase */
static int
square_sample(int p, int phase)
{
/* amplified IRE = ((mV / 7.143) - 312 / 7.143) * 1024 */
/* https://www.nesdev.org/wiki/NTSC_video#Brightness_Levels */
static int IRE[16] = {
/* 0d 1d 2d 3d */
-12042, 0, 34406, 81427,
/* 0d 1d 2d 3d emphasized */
-17203,-8028, 19497, 57342,
/* 00 10 20 30 */
43581, 75693, 112965, 112965,
/* 00 10 20 30 emphasized */
26951, 52181, 83721, 83721
};
static int active[6] = {
0300, 0100,
0500, 0400,
0600, 0200
};
int hue;
int e, l, v;
hue = (p & 0x0f);
/* last two columns are black */
if (hue >= 0x0e) {
return 0;
}
v = (((hue + phase) % 12) < 6);
/* red 0100, green 0200, blue 0400 */
e = (((p & 0700) & active[(phase >> 1) % 6]) > 0);
switch (hue) {
case 0x00: l = 1; break;
case 0x0d: l = 0; break;
default: l = v; break;
}
return IRE[(l << 3) + (e << 2) + ((p >> 4) & 3)];
}
#define NES_OPTIMIZED 1
/* toggle drawing of NES border
* (normally not in visible region, but it depends on your emulator)
* highly recommended to keep disabled for better performance if the border
* is not visible in your emulator.
*/
#define NES_BORDER 0
/* the optimized version is NOT the most optimized version, it just performs
* some simple refactoring to prevent a few redundant computations
*/
#if NES_OPTIMIZED
/* this function is an optimization
* basically factoring out the field setup since as long as CRT->analog
* does not get cleared, all of this should remain the same every update
*/
static void
setup_field(struct CRT *v)
{
int n;
for (n = 0; n < CRT_VRES; n++) {
int t; /* time */
signed char *line = &v->analog[n * CRT_HRES];
t = LINE_BEG;
/* vertical sync scanlines */
if (n >= 259 && n <= CRT_VRES) {
while (t < SYNC_BEG) line[t++] = BLANK_LEVEL; /* FP */
while (t < PPUpx2pos(327)) line[t++] = SYNC_LEVEL; /* sync separator */
while (t < CRT_HRES) line[t++] = BLANK_LEVEL; /* blank */
} else {
/* prerender/postrender/video scanlines */
while (t < SYNC_BEG) line[t++] = BLANK_LEVEL; /* FP */
while (t < BW_BEG) line[t++] = SYNC_LEVEL; /* SYNC */
while (t < CRT_HRES) line[t++] = BLANK_LEVEL;
}
}
}
extern void
crt_modulate(struct CRT *v, struct NTSC_SETTINGS *s)
{
int x, y, xo, yo;
int destw = AV_LEN;
int desth = CRT_LINES;
int n, phase;
int iccf[CRT_CC_VPER][CRT_CC_SAMPLES];
int ccburst[CRT_CC_VPER][CRT_CC_SAMPLES]; /* color phase for burst */
int sn, cs;
static int phasetab[CRT_CC_VPER] = { 0, 4, 8 };
if (!s->field_initialized) {
setup_field(v);
s->field_initialized = 1;
}
for (y = 0; y < CRT_CC_VPER; y++) {
xo = (y + s->dot_crawl_offset) * (360 / CRT_CC_VPER);
for (x = 0; x < CRT_CC_SAMPLES; x++) {
n = (s->hue + x * (360 / CRT_CC_SAMPLES) + xo + 33) % 360;
crt_sincos14(&sn, &cs, n * 8192 / 180);
ccburst[y][x] = sn >> 10;
}
}
xo = AV_BEG + s->xoffset;
yo = CRT_TOP + s->yoffset;
/* align signal */
xo = (xo & ~3);
#if NES_BORDER
for (n = CRT_TOP; n <= (CRT_BOT + 2); n++) {
int t; /* time */
signed char *line = &v->analog[n * CRT_HRES];
t = LINE_BEG;
phase = phasetab[(n + s->dot_crawl_offset) % CRT_CC_VPER] + 6;
t = LAV_BEG;
while (t < CRT_HRES) {
int ire, p;
p = s->border_color;
if (t == LAV_BEG) p = 0xf0;
ire = BLACK_LEVEL + v->black_point;
ire += square_sample(p, phase + 0);
ire += square_sample(p, phase + 1);
ire += square_sample(p, phase + 2);
ire += square_sample(p, phase + 3);
ire = (ire * v->white_point / 100) >> 12;
line[t++] = ire;
phase += 3;
}
}
#endif
for (y = 0; y < desth; y++) {
signed char *line;
int t, cb;
int sy = (y * s->h) / desth;
if (sy >= s->h) sy = s->h;
if (sy < 0) sy = 0;
n = (y + yo);
line = &v->analog[n * CRT_HRES];
/* CB_CYCLES of color burst at 3.579545 Mhz */
for (t = CB_BEG; t < CB_BEG + (CB_CYCLES * CRT_CB_FREQ); t++) {
cb = ccburst[n % CRT_CC_VPER][t % CRT_CC_SAMPLES];
line[t] = (BLANK_LEVEL + (cb * BURST_LEVEL)) >> 5;
iccf[n % CRT_CC_VPER][t % CRT_CC_SAMPLES] = line[t];
}
sy *= s->w;
phase = phasetab[(y + yo + s->dot_crawl_offset) % CRT_CC_VPER];
for (x = 0; x < destw; x++) {
int ire, p;
p = s->data[((x * s->w) / destw) + sy];
ire = BLACK_LEVEL + v->black_point;
ire += square_sample(p, phase + 0);
ire += square_sample(p, phase + 1);
ire += square_sample(p, phase + 2);
ire += square_sample(p, phase + 3);
ire = (ire * v->white_point / 100) >> 12;
v->analog[(x + xo) + (y + yo) * CRT_HRES] = ire;
phase += 3;
}
}
for (n = 0; n < CRT_CC_VPER; n++) {
for (x = 0; x < CRT_CC_SAMPLES; x++) {
v->ccf[n][x] = iccf[n][x] << 7;
}
}
}
#else
/* NOT NES_OPTIMIZED */
extern void
crt_modulate(struct CRT *v, struct NTSC_SETTINGS *s)
{
int x, y, xo, yo;
int destw = AV_LEN;
int desth = CRT_LINES;
int n, phase;
int iccf[CRT_CC_VPER][CRT_CC_SAMPLES];
int ccburst[CRT_CC_VPER][CRT_CC_SAMPLES]; /* color phase for burst */
int sn, cs;
static int phasetab[CRT_CC_VPER] = { 0, 4, 8 };
for (y = 0; y < CRT_CC_VPER; y++) {
xo = (y + s->dot_crawl_offset) * (360 / CRT_CC_VPER);
for (x = 0; x < CRT_CC_SAMPLES; x++) {
n = (s->hue + x * (360 / CRT_CC_SAMPLES) + xo + 33) % 360;
crt_sincos14(&sn, &cs, n * 8192 / 180);
ccburst[y][x] = sn >> 10;
}
}
xo = AV_BEG + s->xoffset;
yo = CRT_TOP + s->yoffset;
/* align signal */
xo = (xo & ~3);
for (n = 0; n < CRT_VRES; n++) {
int t; /* time */
signed char *line = &v->analog[n * CRT_HRES];
t = LINE_BEG;
/* vertical sync scanlines */
if (n >= 259 && n <= CRT_VRES) {
while (t < SYNC_BEG) line[t++] = BLANK_LEVEL; /* FP */
while (t < PPUpx2pos(327)) line[t++] = SYNC_LEVEL; /* sync separator */
while (t < CRT_HRES) line[t++] = BLANK_LEVEL; /* blank */
} else {
int cb;
/* prerender/postrender/video scanlines */
while (t < SYNC_BEG) line[t++] = BLANK_LEVEL; /* FP */
while (t < BW_BEG) line[t++] = SYNC_LEVEL; /* SYNC */
while (t < CB_BEG) line[t++] = BLANK_LEVEL; /* BW + CB + BP */
/* CB_CYCLES of color burst at 3.579545 Mhz */
for (t = CB_BEG; t < CB_BEG + (CB_CYCLES * CRT_CB_FREQ); t++) {
cb = ccburst[n % CRT_CC_VPER][t % CRT_CC_SAMPLES];
line[t] = (BLANK_LEVEL + (cb * BURST_LEVEL)) >> 5;
iccf[n % CRT_CC_VPER][t % CRT_CC_SAMPLES] = line[t];
}
while (t < LAV_BEG) line[t++] = BLANK_LEVEL;
#if NES_BORDER
if (n >= CRT_TOP && n <= (CRT_BOT + 2)) {
phase = phasetab[(n + s->dot_crawl_offset) % CRT_CC_VPER] + 6;
while (t < CRT_HRES) {
int ire, p;
p = s->border_color;
if (t == LAV_BEG) p = 0xf0;
ire = BLACK_LEVEL + v->black_point;
ire += square_sample(p, phase + 0);
ire += square_sample(p, phase + 1);
ire += square_sample(p, phase + 2);
ire += square_sample(p, phase + 3);
ire = (ire * v->white_point / 100) >> 12;
line[t++] = ire;
phase += 3;
}
} else {
#endif
while (t < CRT_HRES) line[t++] = BLANK_LEVEL;
#if NES_BORDER
}
#endif
}
}
for (y = 0; y < desth; y++) {
int sy = (y * s->h) / desth;
if (sy >= s->h) sy = s->h;
if (sy < 0) sy = 0;
sy *= s->w;
phase = phasetab[(y + yo + s->dot_crawl_offset) % CRT_CC_VPER];
for (x = 0; x < destw; x++) {
int ire, p;
p = s->data[((x * s->w) / destw) + sy];
ire = BLACK_LEVEL + v->black_point;
ire += square_sample(p, phase + 0);
ire += square_sample(p, phase + 1);
ire += square_sample(p, phase + 2);
ire += square_sample(p, phase + 3);
ire = (ire * v->white_point / 100) >> 12;
v->analog[(x + xo) + (y + yo) * CRT_HRES] = ire;
phase += 3;
}
}
for (n = 0; n < CRT_CC_VPER; n++) {
for (x = 0; x < CRT_CC_SAMPLES; x++) {
v->ccf[n][x] = iccf[n][x] << 7;
}
}
}
#endif
#endif