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spacetaxi/stSim.c
Scott Duensing df36b0ae84 Updates to match JoeyLib.
2026-10-19 15:47:41 -05:00

1794 lines
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// Space Taxi -- the game tick ($5F40 main loop), physics, landing,
// collision, crash sequence, fuel and HUD arithmetic.
//
// Every function names the original routine it mirrors. The order of
// calls inside stSimTick is the order of the JSRs in the C64 main
// loop; the two raster waits that split it are where the VIC latched
// the frame, so the sprite snapshot (marshal) and the collision test
// sit at the same places.
#include <string.h>
#include "stSim.h"
// Jingle selection ($6935 / $70D4). Song numbers index kStSongs.
#define ST_JINGLE_SONG_BONUS 4u // level-25 start and the bonus cab
#define ST_JINGLE_LEVEL_25 0x19u // $7215 compared against #$19
// The descent lamp ($6419): two cell pairs beside the fuel gauge, the
// colors they light in, and the Y velocities that pick one.
#define ST_LAMP_CELL_SLOW ST_CELL(23, 10) // $DBA2
#define ST_LAMP_CELL_FAST ST_CELL(24, 10) // $DBCA
#define ST_LAMP_OFF 0x0Bu // dark gray
#define ST_LAMP_SLOW 0x03u // cyan
#define ST_LAMP_FALL 0x07u // yellow
#define ST_LAMP_FAST 0x02u // red
#define ST_LAMP_FALL_VEL 0x0080 // high byte 0, low bit 7
#define ST_LAMP_FAST_VEL 0x0100 // high byte positive
#define ST_LAMP_TICK_MASK 7u // $71BE counts mod 8...
#define ST_LAMP_LIT_TICKS 5u // ...and lights on 0..4
// Screen-code strings the engine writes (all ASCII-compatible glyphs).
// $6C38 -- the 12-character blank that clears the message row (every
// message is 12 characters: "PAD PLEASE", " UP PLEASE! " and the rest).
static const uint8_t kTextBlank[] = " ";
// $43B1 -- the fare meter's blank template: three leading blanks, then
// "0.00" in the inverse-video digit glyphs.
static const uint8_t kHudTemplate[ST_NUMBER_CHARS] = { 0x66, 0x66, 0x66, 0x74, 0x77, 0x74, 0x74 };
// Fuel-pump chirp frequencies while refuelling ($6DFA, indexed by the
// mod-8 pump tick 1..4).
static const uint8_t kPumpFreq[5] = { 0x04, 0x05, 0x07, 0x0A, 0x10 };
const uint8_t kStBit[ST_HW_SPRITES] = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80 };
static void applyVelocityX(StSimT *sim);
static void applyVelocityY(StSimT *sim);
static bool backgroundRowHits(const StSimT *sim, int16_t firstCol, int16_t py, const uint8_t *w);
static bool cabRowsTouchBackground(StSimT *sim, int16_t firstCol, int16_t py, uint8_t phase);
static const uint8_t *cabWindows(StSimT *sim, uint8_t s);
static int16_t cellOfPixel(int16_t px);
static void collisionDispatch(StSimT *sim);
static void collisionPhase1(StSimT *sim);
static void collisionPhase2(StSimT *sim);
static StTickResultE collisionPhase3(StSimT *sim);
static void computeCollisions(StSimT *sim);
static bool coveringCellsSolid(const StSimT *sim, int16_t firstCol, int16_t topRow, int16_t botRow);
static void crashStart(StSimT *sim);
static void drawCabIcons(StSimT *sim);
static void drawScreensCount(StSimT *sim);
static void edgeReflect(StSimT *sim);
static void fireButtonEdge(StSimT *sim);
static uint8_t frameBgCollisions(StSimT *sim);
static uint8_t frameSpriteCollisions(StSimT *sim);
static void fuelBarHud(StSimT *sim);
static void fuelTick(StSimT *sim);
static void hudDraw(StSimT *sim);
static void landedHandler(StSimT *sim);
static bool levelEndCheck(const StSimT *sim);
static void markCell(StSimT *sim, uint16_t cell);
static void padDetect(StSimT *sim);
static void padLandingBob(StSimT *sim);
static void passengerArrTick(StSimT *sim);
static void physicsTick(StSimT *sim);
static uint8_t readInput(StSimT *sim);
static void rowWindow(const uint8_t *row, uint8_t s, uint8_t *w);
static void setCell(StSimT *sim, uint16_t cell, uint8_t ch);
static void setColorCell(StSimT *sim, uint16_t cell, uint8_t color);
static void sfxEnvelopeTick(StSimT *sim);
static void spriteMasks(StSimT *sim, uint8_t idx);
static bool spriteRowsTouchBackground(const StSimT *sim, uint8_t idx, int16_t firstCol, int16_t py, uint8_t phase);
static bool spriteTouchesBackground(StSimT *sim, uint8_t idx);
static void spritesOffReset(StSimT *sim);
static bool spritesTouch(StSimT *sim, uint8_t a, uint8_t b, int16_t dx, int16_t dy);
static void taxiSpawnInit(StSimT *sim);
static void taxiSpriteCelSelect(StSimT *sim);
static uint8_t validateDigit(uint8_t ch);
static void voicesOff(StSimT *sim);
// $6112 -- add the X velocity to the 17-bit X position (msb:col:frac)
// and refresh the sprite-0 column shadow.
static void applyVelocityX(StSimT *sim) {
uint16_t pos = (uint16_t)(((uint16_t)sim->posXcol << 8) | sim->posXlo);
uint32_t sum = (uint32_t)pos + (uint16_t)sim->velX;
uint8_t msb = (uint8_t)(sim->posXmsb + (uint8_t)(sum >> 16));
if (sim->velX < 0) {
msb++;
}
sim->posXmsb = (uint8_t)(msb & 1u);
sim->posXlo = (uint8_t)sum;
sim->posXcol = (uint8_t)(sum >> 8);
sim->spr[0].msb = sim->posXmsb;
sim->spr[0].col = sim->posXcol;
}
// $6145 -- Y: velocity += accel + gravity, position += velocity.
static void applyVelocityY(StSimT *sim) {
uint16_t pos;
sim->velY = (int16_t)((uint16_t)sim->accelY + sim->gravTemplateY + (uint16_t)sim->velY);
pos = (uint16_t)(((uint16_t)sim->posYrow << 8) | sim->posYlo);
pos = (uint16_t)(pos + (uint16_t)sim->velY);
sim->posYlo = (uint8_t)pos;
sim->posYrow = (uint8_t)(pos >> 8);
sim->spr[0].row = sim->posYrow;
}
// Whether a 4-byte row window (rowWindow: byte j covers character
// column firstCol + j) meets character graphics on screen pixel row py.
static bool backgroundRowHits(const StSimT *sim, int16_t firstCol, int16_t py, const uint8_t *w) {
uint8_t glyphRow;
uint8_t j;
if (py < 0 || py >= (int16_t)(ST_SCREEN_ROWS * 8u)) {
return false;
}
glyphRow = (uint8_t)(py & 7);
for (j = 0u; j < 4u; j++) {
int16_t col = (int16_t)(firstCol + (int16_t)j);
if (w[j] != 0u && col >= 0 && col < (int16_t)ST_SCREEN_COLS) {
if ((stSimGlyphRow(sim, sim->screen[ST_CELL((uint16_t)py >> 3, (uint16_t)col)], glyphRow) & w[j]) != 0u) {
return true;
}
}
}
return false;
}
// The cab's 21 cached row windows at grid phase `phase` against the
// background rows under it.
static bool cabRowsTouchBackground(StSimT *sim, int16_t firstCol, int16_t py, uint8_t phase) {
uint8_t first = sim->collRowFirst[0];
uint8_t left = (uint8_t)(sim->collRowLast[0] + 1u - first);
const uint8_t *win;
if (first == ST_SPRITE_H) {
return false;
}
win = cabWindows(sim, phase) + (uint16_t)first * 4u;
py = (int16_t)(py + first);
// Counted down to zero: `dec a / bne` needs no compare. (It also
// dodged the llvm816 bug, fixed 2026-09-22, where the up-counting form
// compiled to `cmp #end / inc a / bne` with the inc trampling the
// compare's Z, so the loop ran past row 20 into the next phase's
// windows -- the false landing crash in the IIgs "Puzzles" demo.)
do {
if (backgroundRowHits(sim, firstCol, py, win)) {
return true;
}
win += 4;
py++;
left--;
} while (left != 0u);
return false;
}
// The cab's 21 row windows at grid phase s, 4 bytes per row, built on
// first use after the cab's mask changed and cached until it changes
// again. The cab is one side of every collision test, so no test
// shifts a row (a variable 32-bit shift is a library bit loop on the
// 65816 and this was the collision test's whole cost).
static const uint8_t *cabWindows(StSimT *sim, uint8_t s) {
uint8_t (*win)[4] = sim->cabWin[s];
uint8_t r;
if ((sim->cabWinValid & (uint8_t)(1u << s)) == 0u) {
for (r = 0u; r < ST_SPRITE_H; r++) {
rowWindow(sim->collMask[0][r], s, win[r]);
}
sim->cabWinValid |= (uint8_t)(1u << s);
}
return &win[0][0];
}
// Which character column (or row) a pixel coordinate falls in: floor
// division by 8. A shift, not a divide -- the 65816 has no divider and
// the compiler's signed-division helper cost more than the collision
// test that calls it. The +256/-32 bias makes the shift exact for any
// coordinate down to -256, well past the furthest a sprite can hang off
// the left or top edge.
static int16_t cellOfPixel(int16_t px) {
return (int16_t)(((px + 256) >> 3) - 32);
}
// $6966 -- latch the frame's collisions and run the crash phases.
static void collisionDispatch(StSimT *sim) {
computeCollisions(sim);
if (sim->collisionPhase != 0u) {
// Phases 1..3 dispatch elsewhere (stSimTick handles 3's exit).
return;
}
stFarePadLightingGate(sim);
if ((sim->spriteBgColl & 1u) == 0u) {
if ((sim->spriteSpriteColl & 1u) == 0u) {
return;
}
if (sim->deathInProgress != 0u) {
return;
}
if ((sim->spriteSpriteColl & 2u) != 0u) {
if ((sim->spriteSpriteColl & 0xF8u) != 0u) {
return;
}
stFareSquashed(sim);
}
if ((sim->spriteSpriteColl & 0xF8u) == 0u) {
return;
}
}
// $6A01: the level's verdict on sprite contact; background contact
// always kills.
sim->hitDispatchResult = stHookHitVerdict(sim);
if ((sim->spriteBgColl & 1u) == 0u) {
if (sim->hitDispatchResult == 0u) {
return;
}
}
crashStart(sim);
}
// $6A72 -- the wreck falls: every second tick sweep the scream, flip
// the debris cel, jitter, reflect off the side walls, drift with the
// old X velocity and accelerate down until row $DA.
static void collisionPhase1(StSimT *sim) {
uint8_t jitter;
uint16_t sum;
if ((sim->hitDispatchResult & 0x80u) == 0u) {
sim->phaseTimer--;
if (sim->phaseTimer != 0u) {
return;
}
sim->phaseTimer = sim->phaseReload;
sim->thrustSweep--;
stAudioThrustSweep((uint8_t)(sim->thrustSweep >> 1));
sim->spr[0].ptr ^= 1u;
// $6A98: rng(5) - 3 added to the sprite column (msb follows).
jitter = (uint8_t)(stSimRng(sim, 5u) - 3u);
stSimSpriteAddX(sim, 0u, jitter);
edgeReflect(sim);
applyVelocityX(sim);
// vy += 40 (low byte with carry into the high byte), row += vy hi.
sum = (uint16_t)((uint16_t)(sim->velY & 0xFFu) + 0x28u);
sim->velY = (int16_t)((uint16_t)(((uint16_t)sim->velY & 0xFF00u) + (sum & 0x100u)) | (sum & 0xFFu));
sim->spr[0].row = (uint8_t)(sim->spr[0].row + (uint8_t)((uint16_t)sim->velY >> 8));
if (sim->spr[0].row < 0xDAu) {
return;
}
sim->spr[0].row = 0xDAu;
}
// $6AD6: hit the floor -> phase 2 with a fresh 2-tick cadence.
sim->collisionPhase++;
sim->phaseReload = 2u;
sim->phaseTimer = 2u;
stSimSfx(sim, stC64SfxProgram(ST_SFX_IMPACT));
}
// $6B24 -- walk the wreck cels $CC..$D1 at a slowing rate, then hide.
static void collisionPhase2(StSimT *sim) {
sim->phaseTimer--;
if (sim->phaseTimer != 0u) {
return;
}
sim->phaseReload++;
sim->phaseTimer = sim->phaseReload;
sim->spr[0].ptr++;
if (sim->spr[0].ptr != ST_SPRITE_WRECK_LAST) {
return;
}
sim->spr[0].enable = 0u;
sim->collisionPhase++;
sim->phaseTimer = 0x46u;
}
// $6B4C -- 70-tick pause, then the life bookkeeping.
static StTickResultE collisionPhase3(StSimT *sim) {
sim->phaseTimer--;
if (sim->phaseTimer != 0u) {
return ST_TICK_CONTINUE;
}
if (sim->demoMode != 0u) {
return ST_TICK_CRASH_DONE;
}
return stSimLoseCab(sim);
}
// $6966 -- what its read of $D01E/$D01F sees: this tick's frame OR the
// frame drawn before the flush (see prevFrameSpriteColl in StSimT).
static void computeCollisions(StSimT *sim) {
uint8_t ss = frameSpriteCollisions(sim);
sim->spriteSpriteColl = (uint8_t)(ss | sim->prevFrameSpriteColl);
sim->spriteBgColl = (uint8_t)(frameBgCollisions(sim) | sim->prevFrameBgColl);
sim->prevFrameSpriteColl = ss;
}
// Whether any character cell in rows topRow..botRow, columns firstCol..
// firstCol+3 (the cells a sprite at that spot covers) is non-blank.
static bool coveringCellsSolid(const StSimT *sim, int16_t firstCol, int16_t topRow, int16_t botRow) {
int16_t rr;
int16_t cc;
for (rr = topRow; rr <= botRow; rr++) {
for (cc = firstCol; cc <= (int16_t)(firstCol + 3); cc++) {
if (cc >= 0 && cc < (int16_t)ST_SCREEN_COLS && sim->screen[ST_CELL((uint16_t)rr, (uint16_t)cc)] != ST_CHAR_SPACE) {
return true;
}
}
}
return false;
}
// $6A2B -- start the wreck sequence.
static void crashStart(StSimT *sim) {
sim->spr[0].ptr = ST_SPRITE_WRECK_FIRST;
sim->collisionPhase++;
sim->phaseTimer = 2u;
sim->phaseReload = 2u;
stAudioNoise(false);
sim->eventDispatchType = ST_EVENT_NONE;
sim->activePad = 0u;
sim->spr[2].enable = 0u;
sim->spr[2].row = 0u;
sim->velY = 0x0303;
stSimSfx(sim, stC64SfxProgram(ST_SFX_CRASH));
sim->thrustSweep = 0xA0u;
if (sim->stage == ST_STAGE_WALK_TO_CAB) {
sim->stage--;
}
}
// $6372 -- one cab icon per spare cab (cabs - 1 of them).
static void drawCabIcons(StSimT *sim) {
uint8_t k = sim->cabs[sim->player];
while (k > 1u) {
k--;
setCell(sim, (uint16_t)(ST_CELL_CAB_ICONS + k), ST_CHAR_CAB_ICON);
}
}
// $6384 -- screens completed, or the finished marker past 25.
static void drawScreensCount(StSimT *sim) {
uint8_t v = sim->levelState;
uint8_t tens = 0u;
if (v >= 0x19u) {
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 0u), 0xCBu);
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 1u), 0xCCu);
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 2u), 0xCDu);
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 3u), 0xCEu);
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 4u), 0xCFu);
return;
}
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 2u), 0xCAu);
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 3u), ST_CHAR_ZERO);
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 4u), ST_CHAR_ZERO);
while (v >= 10u) {
v = (uint8_t)(v - 10u);
tens++;
}
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 1u), (v == 0u) ? ST_CHAR_ZERO : (uint8_t)(ST_CHAR_DIGIT_BASE + v));
setCell(sim, (uint16_t)(ST_CELL_SCREENS + 0u), (tens == 0u) ? ST_CHAR_BLANK : (uint8_t)(ST_CHAR_DIGIT_BASE + tens));
}
// $6AED -- negate the X velocity when the wreck crosses column 23
// leftward or column 65 (in the high half) rightward.
static void edgeReflect(StSimT *sim) {
bool reflect = false;
if (sim->spr[0].msb == 0u) {
if (sim->velX < 0 && sim->spr[0].col < 0x17u) {
reflect = true;
}
} else {
if (sim->velX >= 0 && sim->spr[0].col >= 0x41u) {
reflect = true;
}
}
if (reflect) {
sim->velX = (int16_t)(-sim->velX);
}
}
// $63DD -- FIRE press edge while airborne toggles the landing gear.
static void fireButtonEdge(StSimT *sim) {
if (sim->activePad != 0u) {
return;
}
if (sim->fireWasHeld != 0u) {
sim->fireWasHeld = (uint8_t)(sim->inputMask & 0x10u);
return;
}
if ((sim->inputMask & 0x10u) == 0u) {
return;
}
sim->fireWasHeld = 0x10u;
sim->spr[0].ptr ^= 1u;
stSimSfx(sim, stC64SfxProgram(ST_SFX_GEAR));
}
// $6D6A -- sprite 2 is the exhaust: two columns left of the cab,
// visible every other tick while a direction is held.
void stSimFlameUpdate(StSimT *sim) {
uint16_t x;
if (sim->dirMask == 0u) {
stAudioNoise(false);
sim->spr[2].enable = 0u;
return;
}
stAudioNoise(true);
x = (uint16_t)(stSimSpriteX(sim, 0u) - 2u);
sim->spr[2].col = (uint8_t)x;
sim->spr[2].msb = (uint8_t)(x >> 8);
sim->spr[2].row = sim->spr[0].row;
sim->flameParity ^= 1u;
if (sim->flameParity == 0u) {
sim->spr[2].enable = 0u;
return;
}
sim->spr[2].ptr = stC64FlameCel(sim->dirMask & 0x0Fu);
sim->spr[2].enable = 1u;
}
// The displayed frame's $D01F bits over the current picture -- only the
// bits anyone reads: the cab's, and those of the hazards levels J and P
// opt in through bgCollSprites.
static uint8_t frameBgCollisions(StSimT *sim) {
uint8_t bg = 0u;
uint8_t b;
for (b = 0u; b < ST_HW_SPRITES; b++) {
if ((sim->frame.enableMask & kStBit[b]) == 0u) {
continue;
}
if (b != 0u && (sim->bgCollSprites & kStBit[b]) == 0u) {
continue;
}
spriteMasks(sim, b);
if (spriteTouchesBackground(sim, b)) {
bg |= kStBit[b];
}
}
return bg;
}
// The displayed frame's $D01E: both bits of every pair of shown sprites
// whose pixels meet -- any pair, because the hooks test whole groups of
// bits (G's and the dispatch's AND #$F8 also catch a hook sprite touching
// the exhaust flame or another hook sprite, H's and U's walk every bit,
// and the pad light's AND #$02 catches the passenger touching anything).
static uint8_t frameSpriteCollisions(StSimT *sim) {
uint8_t shown = sim->frame.enableMask;
uint8_t ss = 0u;
uint8_t a;
uint8_t b;
for (a = 0u; a < (uint8_t)(ST_HW_SPRITES - 1u); a++) {
if ((shown & kStBit[a]) == 0u) {
continue;
}
for (b = (uint8_t)(a + 1u); b < ST_HW_SPRITES; b++) {
uint8_t pair = (uint8_t)(kStBit[a] | kStBit[b]);
int16_t dx;
int16_t dy;
// A pair already latched on both sides cannot add a bit, and
// most pairs are too far apart to test at all.
if ((shown & kStBit[b]) == 0u || (ss & pair) == pair) {
continue;
}
dx = (int16_t)((int16_t)sim->frame.x[b] - (int16_t)sim->frame.x[a]);
dy = (int16_t)((int16_t)sim->frame.y[b] - (int16_t)sim->frame.y[a]);
if (dx <= -ST_SPRITE_W || dx >= ST_SPRITE_W || dy <= -ST_SPRITE_H || dy >= ST_SPRITE_H) {
continue;
}
if (spritesTouch(sim, a, b, dx, dy)) {
ss |= pair;
}
}
}
return ss;
}
// $6419 -- the descent lamp beside the fuel gauge. Every tick its two
// cell pairs ($DBA2 on row 23, $DBCA on row 24) go dark gray; then, on
// five ticks of every eight, one pair lights by the Y velocity
// ($714F/$714E, positive = falling): red on row 24 when the high byte is
// positive ($643D), yellow on row 23 when it is zero and the low byte has
// bit 7 set ($6450), and cyan on row 23 otherwise ($6449) -- any climb,
// a hover and a slow fall alike.
static void fuelBarHud(StSimT *sim) {
uint16_t cell = ST_LAMP_CELL_SLOW;
uint8_t color = ST_LAMP_SLOW;
setColorCell(sim, ST_LAMP_CELL_SLOW, ST_LAMP_OFF);
setColorCell(sim, (uint16_t)(ST_LAMP_CELL_SLOW + 1u), ST_LAMP_OFF);
setColorCell(sim, ST_LAMP_CELL_FAST, ST_LAMP_OFF);
setColorCell(sim, (uint16_t)(ST_LAMP_CELL_FAST + 1u), ST_LAMP_OFF);
sim->fuelBarTick = (uint8_t)((sim->fuelBarTick + 1u) & ST_LAMP_TICK_MASK);
if (sim->fuelBarTick >= ST_LAMP_LIT_TICKS) {
return;
}
if (sim->velY >= ST_LAMP_FAST_VEL) {
color = ST_LAMP_FAST;
cell = ST_LAMP_CELL_FAST;
} else if (sim->velY >= ST_LAMP_FALL_VEL) {
color = ST_LAMP_FALL;
}
setColorCell(sim, cell, color);
setColorCell(sim, (uint16_t)(cell + 1u), color);
}
// $6E23 -- the fuel gauge: half a cell burns every fuelRate ticks in
// the air; on the fuel pad (the extra last pad) it refills at ten
// cents per half cell.
static void fuelTick(StSimT *sim) {
const StLevelT *L = sim->level;
uint8_t x;
if (sim->activePad == sim->padCount && sim->activePad != sim->specialPad) {
if (sim->screen[ST_CELL_FUEL_LAST] == ST_CHAR_BLANK) {
return;
}
if (!stSimDecrementNumber(sim, ST_CELL_SCORE, 5u)) {
return;
}
sim->padAnimTick = (uint8_t)((sim->padAnimTick + 1u) & 7u);
if (sim->padAnimTick == 0u) {
stSimSfx(sim, stC64SfxProgram(ST_SFX_CASH));
} else if (sim->padAnimTick < 5u) {
stAudioVoice1Freq(kPumpFreq[sim->padAnimTick]);
}
if (sim->padAnimTick != 0u) {
return;
}
x = sim->fuelCells;
if (sim->screen[ST_CELL_FUEL + x] == ST_CHAR_BLANK) {
x++;
sim->fuelCells = x;
setCell(sim, (uint16_t)(ST_CELL_FUEL + x), ST_CHAR_FUEL_HALF);
return;
}
setCell(sim, (uint16_t)(ST_CELL_FUEL + x), ST_CHAR_BLANK);
if (sim->screen[ST_CELL_FUEL_LAST] == ST_CHAR_BLANK) {
stSimSfx(sim, stC64SfxProgram(ST_SFX_FUEL_FULL));
}
return;
}
// $6EAA
if (sim->activePad != 0u) {
return;
}
sim->fuelCountdown--;
if (sim->fuelCountdown != 0u) {
return;
}
if (sim->fuelCells < 3u) {
stSimSfx(sim, stC64SfxProgram(ST_SFX_FUEL_LOW));
}
sim->fuelCountdown = L->fuelRate;
x = sim->fuelCells;
if (sim->screen[ST_CELL_FUEL] == ST_CHAR_FUEL_HALF) {
return;
}
if (sim->screen[ST_CELL_FUEL + x] == ST_CHAR_FUEL_HALF) {
setCell(sim, (uint16_t)(ST_CELL_FUEL + x), ST_CHAR_FUEL_EMPTY);
x--;
sim->fuelCells = x;
return;
}
setCell(sim, (uint16_t)(ST_CELL_FUEL + x), ST_CHAR_FUEL_HALF);
}
// $43E5 -- the fare meter loses a penny every tick.
static void hudDraw(StSimT *sim) {
(void)stSimDecrementNumber(sim, ST_CELL_FARE, 6u);
}
// $657B -- parked on a pad: wait for UP to be released, then UP takes
// off (velocities cleared, gear retracted).
static void landedHandler(StSimT *sim) {
if (sim->activePadMirror != 0u) {
if ((sim->inputMask & 1u) == 0u) {
sim->activePadMirror = 0u;
}
return;
}
if (sim->deathInProgress != 0u) {
return;
}
if ((sim->inputMask & 1u) == 0u) {
return;
}
sim->velY = 0;
sim->velX = 0;
sim->activePad = 0u;
sim->spr[0].ptr &= 0xFEu;
if (sim->stage == ST_STAGE_WALK_TO_CAB) {
sim->stage--;
}
}
// $6BE7 -- the cab has flown out of the top of the screen.
static bool levelEndCheck(const StSimT *sim) {
return sim->posYrow < 0x1Bu;
}
// $645C -- with the gear down and a slow descent, an exact row match
// inside a pad's X bounds is a landing.
static void padDetect(StSimT *sim) {
int8_t i;
if (sim->activePad != 0u) {
return;
}
if ((sim->spr[0].ptr & 1u) == 0u) {
return;
}
if (((uint16_t)sim->velY >> 8) != 0u) {
return;
}
for (i = (int8_t)(sim->padCount - 1u); i >= 0; i--) {
const StPadT *p = &sim->pads[i];
int16_t taxiX = (int16_t)(((uint16_t)sim->posXmsb << 8) | sim->posXcol);
int16_t x1 = (int16_t)(((int16_t)p->x1Hi << 8) | p->x1Lo);
int16_t x2 = (int16_t)(((int16_t)p->x2Hi << 8) | p->x2Lo);
if (sim->spr[0].row != p->row) {
continue;
}
if ((int16_t)(taxiX - x1) < 0) {
continue;
}
if ((int16_t)(x2 - taxiX) < 0) {
continue;
}
sim->activePad = (uint8_t)(i + 1);
sim->activePadMirror = sim->activePad;
sim->eventDispatchType = ST_EVENT_NONE;
if (sim->activePad != sim->activeSpriteIdx) {
if (sim->stage == ST_STAGE_RIDING) {
sim->eventDispatchType = (sim->activeSpriteIdx == ST_FARE_DEST_UP) ? ST_EVENT_WRONG_PAD_UP : ST_EVENT_WRONG_PAD;
} else if (sim->stage == ST_STAGE_WAIT) {
sim->eventDispatchType = ST_EVENT_HAIL;
}
}
sim->dirMask = 0u;
sim->deathInProgress = 1u;
stSimPadLight(sim, true);
sim->bobTimer = 2u;
if (((uint8_t)sim->velY & 0x80u) == 0u) {
stSimSfx(sim, stC64SfxProgram(ST_SFX_LAND_SOFT));
return;
}
sim->bobTimer = 8u;
stSimSfx(sim, stC64SfxProgram(ST_SFX_LAND_HARD));
if (sim->stage == ST_STAGE_RIDING) {
stSimHudInit(sim);
}
return;
}
}
// $6DFF -- the touchdown bob: the sprite dips and rises while the
// timer runs down.
static void padLandingBob(StSimT *sim) {
if (sim->bobTimer == 0u) {
return;
}
sim->bobTimer--;
if ((sim->bobTimer & 1u) != 0u) {
sim->spr[0].row--;
return;
}
sim->spr[0].row++;
if (sim->bobTimer == 0u) {
sim->deathInProgress = 0u;
stSimPadLight(sim, false);
}
}
// $70B1 -- one bonus cab when the score's hundreds digit reaches 3.
static void passengerArrTick(StSimT *sim) {
uint8_t p = sim->player;
if (sim->bonusLatch[p] != 0u) {
return;
}
if (sim->screen[ST_CELL_SCORE + 1u] < 0x6Du) {
return;
}
sim->cabs[p]++;
sim->bonusLatch[p] = sim->cabs[p];
setCell(sim, (uint16_t)(ST_CELL_CAB_ICONS - 1u + sim->cabs[p]), ST_CHAR_CAB_ICON);
// $70D4: the bonus-cab jingle (song 4), blocking.
sim->jingleRequest = (uint8_t)(ST_JINGLE_SONG_BONUS + 1u);
}
// $6032 -- input, thrust, gravity, integration.
static void physicsTick(StSimT *sim) {
uint8_t in;
sim->accelX = 0;
sim->accelY = 0;
in = readInput(sim);
in = stHookInput(sim, in);
sim->inputMask = in;
if (sim->activePad != 0u) {
landedHandler(sim);
return;
}
if (sim->screen[ST_CELL_FUEL] == ST_CHAR_FUEL_HALF) {
// The leftmost cell is down to its last half: out of fuel, so
// only FIRE survives and there is no thrust at all.
sim->inputMask &= 0x10u;
} else {
if ((sim->inputMask & 0x0Cu) != 0u) {
if ((sim->spr[0].ptr & 1u) != 0u) {
sim->inputMask &= 0x13u;
} else {
sim->accelX = (int16_t)sim->accelTemplateX;
if ((sim->inputMask & 0x08u) == 0u) {
sim->accelX = (int16_t)(-sim->accelX);
}
}
}
if ((sim->inputMask & 0x03u) != 0u) {
sim->accelY = (int16_t)sim->accelTemplateY;
if ((sim->inputMask & 0x02u) == 0u) {
sim->accelY = (int16_t)(-sim->accelY);
}
}
}
sim->dirMask = (uint8_t)(sim->inputMask & 0x0Fu);
sim->velX = (int16_t)((uint16_t)sim->accelX + sim->gravTemplateX + (uint16_t)sim->velX);
applyVelocityX(sim);
applyVelocityY(sim);
}
// $6040 + $48F2 -- the joystick byte, or the recorded demo mask.
static uint8_t readInput(StSimT *sim) {
uint8_t mask;
uint16_t next;
if (sim->demoMode == 0u || sim->postMortem != 0u) {
return sim->rawInput;
}
mask = sim->demoBuf[sim->demoOff];
sim->demoTimer--;
if (sim->demoTimer == 0u) {
next = (uint16_t)(sim->demoOff + 3u);
if (next < sizeof(sim->demoBuf)) {
sim->demoTimer = sim->demoBuf[next];
}
next = (uint16_t)(sim->demoOff + 2u);
if (next < sizeof(sim->demoBuf)) {
sim->demoOff = next;
}
}
return mask;
}
static void markCell(StSimT *sim, uint16_t cell) {
if (sim->cellDirty[cell] != 0u) {
return;
}
sim->cellDirty[cell] = 1u;
if (sim->dirtyCount < (uint16_t)(sizeof(sim->dirtyList) / sizeof(sim->dirtyList[0]))) {
sim->dirtyList[sim->dirtyCount++] = cell;
} else {
sim->dirtyAll = true;
}
}
// ---- glyph reverse index (see StSimT in stSim.h) --------------------
// Take `cell` out of the list of whatever glyph it currently shows.
// Reads sim->screen[cell], so call it BEFORE the new character lands.
static void glyphIndexUnlink(StSimT *sim, uint16_t cell) {
uint16_t prev = sim->cellPrev[cell];
uint16_t next = sim->cellNext[cell];
if (prev == ST_GLYPH_CELL_NONE) {
sim->glyphHead[sim->screen[cell]] = next;
} else {
sim->cellNext[prev] = next;
}
if (next != ST_GLYPH_CELL_NONE) {
sim->cellPrev[next] = prev;
}
}
// Push `cell` onto the front of glyph `ch`'s list.
static void glyphIndexLink(StSimT *sim, uint16_t cell, uint8_t ch) {
uint16_t head = sim->glyphHead[ch];
sim->cellPrev[cell] = ST_GLYPH_CELL_NONE;
sim->cellNext[cell] = head;
if (head != ST_GLYPH_CELL_NONE) {
sim->cellPrev[head] = cell;
}
sim->glyphHead[ch] = cell;
}
// Re-derive every list from screen[]. Bulk screen writes (level load,
// title, the blanked intro) bypass setCell, and all of them call
// stSimDirtyAll, so that is the one place this has to hang off.
static void glyphIndexRebuild(StSimT *sim) {
uint16_t cell;
uint16_t k;
for (k = 0u; k < ST_CHARSET_CHARS; k++) {
sim->glyphHead[k] = ST_GLYPH_CELL_NONE;
}
// Built back to front, so each list comes out in ASCENDING cell
// order and the repaint walk moves forward through the stage the
// way the old span scan did.
cell = ST_SCREEN_CELLS;
while (cell != 0u) {
cell--;
glyphIndexLink(sim, cell, sim->screen[cell]);
}
}
// A sprite row (3 bytes, leftmost pixel = bit 7 of byte 0) shifted
// right by s (0..7) into a 4-byte window whose byte j holds the row's
// pixels 8j-s .. 8j-s+7: the row aligned to a grid of 8-pixel cells
// that its left edge sits s pixels into. Fixed shifts by 4, 2 and 1
// on 16-bit halves -- a variable-count shift is a library bit loop on
// the 65816, and a byte carry chain gets folded back into one.
static void rowWindow(const uint8_t *row, uint8_t s, uint8_t *w) {
uint16_t hi = (uint16_t)(((uint16_t)row[0] << 8) | row[1]);
uint16_t lo = (uint16_t)((uint16_t)row[2] << 8);
if ((s & 4u) != 0u) {
lo = (uint16_t)((lo >> 4) | (uint16_t)(hi << 12));
hi = (uint16_t)(hi >> 4);
}
if ((s & 2u) != 0u) {
lo = (uint16_t)((lo >> 2) | (uint16_t)(hi << 14));
hi = (uint16_t)(hi >> 2);
}
if ((s & 1u) != 0u) {
lo = (uint16_t)((lo >> 1) | (uint16_t)(hi << 15));
hi = (uint16_t)(hi >> 1);
}
w[0] = (uint8_t)(hi >> 8);
w[1] = (uint8_t)hi;
w[2] = (uint8_t)(lo >> 8);
w[3] = (uint8_t)lo;
}
static void setCell(StSimT *sim, uint16_t cell, uint8_t ch) {
if (sim->screen[cell] != ch) {
glyphIndexUnlink(sim, cell);
sim->screen[cell] = ch;
glyphIndexLink(sim, cell, ch);
markCell(sim, cell);
}
}
static void setColorCell(StSimT *sim, uint16_t cell, uint8_t color) {
color = (uint8_t)(color & 0x0Fu);
if (sim->color[cell] != color) {
sim->color[cell] = color;
markCell(sim, cell);
}
}
// $4320 -- the release countdown of voices 1 and 2. Gating a voice off
// when its count runs out is the audio layer's business; the counts are
// what the game reads.
static void sfxEnvelopeTick(StSimT *sim) {
uint8_t v;
for (v = 0u; v < ST_SID_TIMED_VOICES; v++) {
if (sim->sidRelTimer[v] != 0u) {
sim->sidRelTimer[v]--;
}
}
}
// 21 rows of 3-byte foreground masks for a displayed sprite, kept in
// collMask[idx] and rebuilt only when its bitmap or multicolor mode
// changes. A multicolor sprite's 2-bit pairs cover two pixels each: a
// non-zero pair is two set mask bits (kPairMask maps a nibble's two
// pairs at once). The cab's cached windows die with its mask.
static void spriteMasks(StSimT *sim, uint8_t idx) {
static const uint8_t kPairMask[16] = {
0x0u, 0x3u, 0x3u, 0x3u, 0xCu, 0xFu, 0xFu, 0xFu,
0xCu, 0xFu, 0xFu, 0xFu, 0xCu, 0xFu, 0xFu, 0xFu
};
const uint8_t *bm = stSimSpriteBitmap(sim, sim->frame.ptr[idx]);
uint8_t multi = (uint8_t)((sim->frame.multiMask & kStBit[idx]) != 0u ? 1u : 0u);
uint8_t *row = sim->collMask[idx][0];
uint16_t n;
uint8_t first;
uint8_t last;
if (bm != 0 && bm == sim->collMaskBm[idx] && multi == sim->collMaskMulti[idx]) {
return;
}
for (n = 0u; n < (uint16_t)(ST_SPRITE_H * 3u); n++) {
uint8_t b = 0u;
if (bm != 0) {
b = bm[n];
if (multi != 0u) {
b = (uint8_t)((kPairMask[b >> 4] << 4) | kPairMask[b & 0x0Fu]);
}
}
row[n] = b;
}
first = ST_SPRITE_H;
last = 0u;
for (n = 0u; n < ST_SPRITE_H; n++) {
if ((row[n * 3u] | row[n * 3u + 1u] | row[n * 3u + 2u]) != 0u) {
if (first == ST_SPRITE_H) {
first = (uint8_t)n;
}
last = (uint8_t)n;
}
}
sim->collRowFirst[idx] = first;
sim->collRowLast[idx] = last;
sim->collMaskBm[idx] = bm;
sim->collMaskMulti[idx] = multi;
if (idx == 0u) {
sim->cabWinValid = 0u;
}
}
// A non-cab sprite's rows (shifted here, only rows with pixels) against
// the background rows under it.
static bool spriteRowsTouchBackground(const StSimT *sim, uint8_t idx, int16_t firstCol, int16_t py, uint8_t phase) {
uint8_t first = sim->collRowFirst[idx];
uint8_t left = (uint8_t)(sim->collRowLast[idx] + 1u - first);
const uint8_t *row;
if (first == ST_SPRITE_H) {
return false;
}
row = sim->collMask[idx][first];
py = (int16_t)(py + first);
// Counted down like cabRowsTouchBackground.
do {
if ((row[0] | row[1] | row[2]) != 0u) {
uint8_t w[4];
rowWindow(row, phase, w);
if (backgroundRowHits(sim, firstCol, py, w)) {
return true;
}
}
row += 3;
py++;
left--;
} while (left != 0u);
return false;
}
// One displayed sprite against the background pixels ($D01F). The
// background can only touch it where a covering character cell is
// non-blank. In open flight every covering cell is the space glyph
// (all-zero pixels), so the 21-row pixel test is skipped there; any
// non-space cell falls through to the exact test, so the result is
// unchanged (space is the only zero-pixel glyph the test can hit).
// Needs spriteMasks(sim, idx) run for this frame first. The row tests
// live in cabRowsTouchBackground / spriteRowsTouchBackground, whose
// loops count DOWN -- see the note there before "simplifying" them.
static bool spriteTouchesBackground(StSimT *sim, uint8_t idx) {
int16_t px = (int16_t)((int16_t)sim->frame.x[idx] - ST_SPRITE_X_ORIGIN);
int16_t py = (int16_t)((int16_t)sim->frame.y[idx] - ST_SPRITE_Y_ORIGIN);
int16_t firstCol = cellOfPixel(px);
int16_t topRow = (py < 0) ? 0 : cellOfPixel(py);
int16_t botRow = cellOfPixel((int16_t)(py + (int16_t)ST_SPRITE_H - 1));
uint8_t phase = (uint8_t)(px - (int16_t)(firstCol << 3));
if (botRow >= (int16_t)ST_SCREEN_ROWS) {
botRow = (int16_t)(ST_SCREEN_ROWS - 1u);
}
if (!coveringCellsSolid(sim, firstCol, topRow, botRow)) {
return false;
}
if (idx == 0u) {
return cabRowsTouchBackground(sim, firstCol, py, phase);
}
return spriteRowsTouchBackground(sim, idx, firstCol, py, phase);
}
// $6946 -- the VIC's sprites off ($D015; the shadow enables are $4248's
// job), the collision latches cleared, nobody on a pad.
static void spritesOffReset(StSimT *sim) {
sim->spriteSpriteColl = 0u;
sim->spriteBgColl = 0u;
sim->activePad = 0u;
sim->activeSpriteIdx = 0u;
}
// Whether shown sprites a < b, b sitting dx right of a and dy below it
// (both inside a sprite's size), have a pixel in common. With dx = 8q - s
// (s in 0..7), b's row byte k lines up with byte k + q of a's row shifted
// to phase s, and only 0 <= k + q <= 3 can overlap; rows r of a meet rows
// r - dy of b, and only the rows where both have pixels are walked. The
// cab's shifted rows are cached (cabWindows) -- it is a side of most
// tests -- any other sprite's are shifted as they are needed.
static bool spritesTouch(StSimT *sim, uint8_t a, uint8_t b, int16_t dx, int16_t dy) {
uint8_t s;
int16_t q;
uint8_t kLo;
uint8_t kHi;
uint8_t r;
uint8_t rHi;
int16_t lo;
int16_t hi;
const uint8_t *win = 0;
const uint8_t *bRow;
uint8_t own[4];
spriteMasks(sim, a);
spriteMasks(sim, b);
if (sim->collRowFirst[a] == ST_SPRITE_H || sim->collRowFirst[b] == ST_SPRITE_H) {
return false;
}
s = (uint8_t)((0 - dx) & (ST_ROW_PHASES - 1));
q = (int16_t)(((dx + (int16_t)s + 32) >> 3) - 4);
kLo = (q < 0) ? (uint8_t)(0 - q) : 0u;
kHi = (q > 1) ? (uint8_t)(3 - q) : 2u;
lo = (int16_t)sim->collRowFirst[a];
hi = (int16_t)(sim->collRowLast[a] + 1);
if ((int16_t)sim->collRowFirst[b] + dy > lo) {
lo = (int16_t)((int16_t)sim->collRowFirst[b] + dy);
}
if ((int16_t)sim->collRowLast[b] + 1 + dy < hi) {
hi = (int16_t)((int16_t)sim->collRowLast[b] + 1 + dy);
}
if (lo >= hi) {
return false;
}
r = (uint8_t)lo;
rHi = (uint8_t)hi;
bRow = sim->collMask[b][(uint8_t)((int16_t)r - dy)];
if (a == 0u) {
win = cabWindows(sim, s) + (uint16_t)r * 4u;
}
for (; r < rHi; r++, bRow += 3) {
const uint8_t *w = win;
uint8_t k;
if (a == 0u) {
win += 4;
} else {
rowWindow(sim->collMask[a][r], s, own);
w = own;
}
for (k = kLo; k <= kHi; k++) {
if ((bRow[k] & w[(uint8_t)((int16_t)k + q)]) != 0u) {
return true;
}
}
}
return false;
}
// $6888 -- place the cab at the level's spawn point with a full tank.
static void taxiSpawnInit(StSimT *sim) {
const StLevelT *L = sim->level;
uint8_t k;
sim->spr[0].enable = 1u;
sim->multiColorMask = 0x07u;
sim->spr[0].ptr = ST_SPRITE_CAB_RIGHT;
sim->posYlo = L->spawn[3];
sim->posYrow = L->spawn[4];
sim->posXlo = L->spawn[0];
sim->posXcol = L->spawn[1];
sim->posXmsb = L->spawn[2];
sim->spr[0].msb = L->spawn[2];
sim->spr[0].col = L->spawn[1];
sim->spr[0].row = L->spawn[4];
sim->velX = 0;
sim->velY = 0;
sim->deathInProgress = 0u;
sim->dirMask = 0u;
sim->inputMask = 0u;
sim->activePad = 0u;
sim->collisionPhase = 0u;
sim->padAnimTick = 0u;
stSimPadLight(sim, false);
fuelBarHud(sim);
sim->fuelCells = 11u;
for (k = 0u; k < ST_FUEL_CELLS; k++) {
setCell(sim, (uint16_t)(ST_CELL_FUEL + k), ST_CHAR_BLANK);
}
sim->fuelCountdown = L->fuelRate;
}
// $619B -- LEFT/RIGHT pick the facing pair; bit 0 (the gear) survives.
static void taxiSpriteCelSelect(StSimT *sim) {
uint8_t gear = (uint8_t)(sim->spr[0].ptr & 1u);
uint8_t base;
if ((sim->dirMask & 0x04u) != 0u) {
base = ST_SPRITE_CAB_LEFT;
} else if ((sim->dirMask & 0x08u) != 0u) {
base = ST_SPRITE_CAB_RIGHT;
} else {
return;
}
sim->spr[0].ptr = (uint8_t)(base | gear);
}
// $4345 -- a HUD glyph's numeric value: blanks and the zero glyph are 0.
static uint8_t validateDigit(uint8_t ch) {
uint8_t v;
if (ch == ST_CHAR_BLANK) {
return 0u;
}
v = (uint8_t)(ch - ST_CHAR_DIGIT_BASE);
if (v == 10u) {
return 0u;
}
return v;
}
// $6909 / $6C02 -- voices 1 and 2 gated off, their release timers cleared.
static void voicesOff(StSimT *sim) {
stAudioSilence();
memset(sim->sidRelTimer, 0, sizeof(sim->sidRelTimer));
}
// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------
// $61FB -- next player's turn; wraps to player 0 when everybody has had
// this screen (the caller then loads the next one).
bool stSimAdvancePlayer(StSimT *sim) {
sim->player++;
if (sim->player == sim->playerCount) {
sim->player = 0u;
return true;
}
return false;
}
// $704E -- keep the current player's score and fare rows.
void stSimArchiveHud(StSimT *sim) {
memcpy(sim->scoreBackup[sim->player], &sim->screen[ST_CELL_SCORE], ST_NUMBER_CHARS);
memcpy(sim->fareBackup[sim->player], &sim->screen[ST_CELL_FARE], ST_NUMBER_CHARS);
}
// $4354 -- add a 7-glyph decimal blob onto the number at dstCell,
// right to left, skipping the decimal point, with leading blanks.
void stSimBcdAdd(StSimT *sim, uint16_t dstCell, const uint8_t *blob) {
int8_t y;
uint8_t carry = 0u;
for (y = 6; y >= 0; y--) {
uint8_t sum;
uint8_t ch;
if (y == 4) {
continue;
}
sum = (uint8_t)(validateDigit(blob[y]) + validateDigit(sim->screen[dstCell + (uint16_t)y]) + carry);
carry = 0u;
if (sum >= 10u) {
carry = 1u;
sum = (uint8_t)(sum - 10u);
}
ch = (uint8_t)(ST_CHAR_DIGIT_BASE + sum);
if (ch == ST_CHAR_DIGIT_BASE) {
ch = ST_CHAR_ZERO;
}
setCell(sim, (uint16_t)(dstCell + (uint16_t)y), ch);
}
// $4393: leading-zero suppression across the integer part.
for (y = 0; y < 3; y++) {
if (sim->screen[dstCell + (uint16_t)y] != ST_CHAR_ZERO) {
break;
}
setCell(sim, (uint16_t)(dstCell + (uint16_t)y), ST_CHAR_BLANK);
}
}
// $6C38 -- blank the message row (color 1, as the original writes it).
void stSimClearMessage(StSimT *sim) {
stSimDrawText(sim, ST_MESSAGE_COL, ST_MESSAGE_ROW, kTextBlank, 1u);
}
// $440B -- subtract one from the digit at `position` of the number at
// `cell`, borrowing leftward. False when there is nothing to take.
bool stSimDecrementNumber(StSimT *sim, uint16_t cell, uint8_t position) {
uint8_t y = position;
uint8_t ch;
for (;;) {
ch = sim->screen[cell + y];
if (ch == ST_CHAR_BLANK) {
return false;
}
if (ch != ST_CHAR_ZERO) {
break;
}
do {
y--;
} while (y == 4u);
}
y = position;
for (;;) {
ch = sim->screen[cell + y];
if (ch != ST_CHAR_ZERO) {
break;
}
setCell(sim, (uint16_t)(cell + y), (uint8_t)(ST_CHAR_DIGIT_BASE + 9u));
do {
y--;
} while (y == 4u);
}
ch = (uint8_t)(ch - 1u);
setCell(sim, (uint16_t)(cell + y), ch);
if (ch != ST_CHAR_DIGIT_BASE) {
return true;
}
setCell(sim, (uint16_t)(cell + y), ST_CHAR_ZERO);
if (y >= 3u) {
return true;
}
if (y == 0u) {
setCell(sim, cell, ST_CHAR_BLANK);
return true;
}
if (sim->screen[cell + y - 1u] != ST_CHAR_BLANK) {
return true;
}
setCell(sim, (uint16_t)(cell + y), ST_CHAR_BLANK);
return true;
}
// $41C2 -- write a screen-code string (terminated by any byte < 6)
// with one color.
void stSimDrawText(StSimT *sim, uint8_t col, uint8_t row, const uint8_t *text, uint8_t color) {
uint16_t cell = ST_CELL(row, col);
while (*text >= 6u) {
setCell(sim, cell, *text);
setColorCell(sim, cell, color);
cell++;
text++;
}
}
// A character's eight 1bpp rows: the game's edit of it, or the const ROM
// glyph when it has never been edited.
const uint8_t *stSimGlyph(const StSimT *sim, uint8_t ch) {
uint8_t slot = sim->glyphSlot[ch];
if (slot != 0u) {
return sim->glyphOverride[slot - 1u].rows;
}
return &stC64Charset()[(uint16_t)ch << 3];
}
// The writable eight rows, copied out of ROM on the first edit. A full
// table parks the edit in the spill entry rather than stealing another
// character's slot: that glyph then simply stays at its ROM form.
uint8_t *stSimGlyphMut(StSimT *sim, uint8_t ch) {
uint8_t slot = sim->glyphSlot[ch];
if (slot == 0u) {
if (sim->glyphOverrideCount >= ST_GLYPH_OVERRIDES) {
return sim->glyphOverride[ST_GLYPH_OVERRIDES].rows;
}
sim->glyphOverrideCount++;
slot = sim->glyphOverrideCount;
sim->glyphSlot[ch] = slot;
memcpy(sim->glyphOverride[slot - 1u].rows, &stC64Charset()[(uint16_t)ch << 3], 8u);
}
return sim->glyphOverride[slot - 1u].rows;
}
// Every glyph back to the ROM set (a scene load).
void stSimGlyphReset(StSimT *sim) {
memset(sim->glyphSlot, 0, sizeof(sim->glyphSlot));
sim->glyphOverrideCount = 0u;
}
// One row of a character's glyph. The collision background test reads
// four of these per sprite row, so it skips the pointer round trip.
uint8_t stSimGlyphRow(const StSimT *sim, uint8_t ch, uint8_t row) {
uint8_t slot = sim->glyphSlot[ch];
if (slot != 0u) {
return sim->glyphOverride[slot - 1u].rows[row];
}
return stC64Charset()[((uint16_t)ch << 3) + row];
}
// $43A5 -- blank the fare meter back to its template.
void stSimHudInit(StSimT *sim) {
uint8_t k;
for (k = 0u; k < ST_NUMBER_CHARS; k++) {
setCell(sim, (uint16_t)(ST_CELL_FARE + k), kHudTemplate[k]);
}
}
// $62F0 + $5F18 -- load the screen image and run the level prelude.
void stSimEnterLevel(StSimT *sim, const StLevelT *level) {
uint8_t k;
sim->level = level;
memcpy(sim->pads, level->pads, sizeof(sim->pads));
sim->padCount = level->padCount;
sim->specialPad = level->specialPad;
sim->bgCollSprites = 0u;
memcpy(sim->screen, level->screen, ST_SCREEN_CELLS);
memcpy(sim->color, level->color, ST_SCREEN_CELLS);
stSimDirtyAll(sim);
stSimGlyphReset(sim);
sim->charDirtyAll = true;
sim->charDirtyCount = 0u;
// Level sprites live in the one level buffer, so the same bitmap
// address now holds other pixels: rebuild every collision mask.
memset(sim->collMaskBm, 0, sizeof(sim->collMaskBm));
sim->borderColor = level->header[0];
sim->bgColor = level->header[1];
sim->spr[0].color = level->header[7];
sim->spr[1].color = level->header[8];
sim->spriteMc0 = level->header[5];
sim->spriteMc1 = level->header[6];
sim->accelTemplateY = level->accelY;
sim->accelTemplateX = level->accelX;
sim->gravTemplateY = level->gravY;
sim->gravTemplateX = level->gravX;
memset(sim->spriteSlots, 0, sizeof(sim->spriteSlots));
sim->fareSlotCount = 0u;
// $634D: this player's HUD rows come back.
for (k = 0u; k < ST_NUMBER_CHARS; k++) {
setCell(sim, (uint16_t)(ST_CELL_SCORE + k), sim->scoreBackup[sim->player][k]);
setCell(sim, (uint16_t)(ST_CELL_FARE + k), sim->fareBackup[sim->player][k]);
}
for (k = 0u; k < 7u; k++) {
setCell(sim, (uint16_t)(ST_CELL_CAB_ICONS + k), ST_CHAR_BLANK);
}
drawCabIcons(sim);
drawScreensCount(sim);
// Prelude $5F18 (the player-turn bookkeeping ran before the load).
for (k = 0u; k < ST_HW_SPRITES; k++) {
sim->spr[k].enable = 0u;
}
sim->hookLevel = level->levelIndex;
stHookSceneLoad(sim);
spritesOffReset(sim);
stHookPrelude0(sim);
stFareTakeoffSetup(sim);
stSimRespawn(sim);
}
// $5F27 -- the respawn half of the prelude.
void stSimRespawn(StSimT *sim) {
taxiSpawnInit(sim);
stHookPrelude1(sim);
// $6906 framePresent: the start-of-screen jingle, then the SID (and
// the demo RNG) reset. $6935: level 25 gets song 4, every other
// screen rotates songs 0..3 on $5E9B. The host plays it with the sim
// frozen, which is what the C64's blocking play-and-wait amounts to.
stSimMarshal(sim);
voicesOff(sim);
sim->jingleRotate++;
if (sim->levelState == ST_JINGLE_LEVEL_25) {
sim->jingleRequest = (uint8_t)(ST_JINGLE_SONG_BONUS + 1u);
} else {
sim->jingleRequest = (uint8_t)((sim->jingleRotate & 3u) + 1u);
}
sim->spriteSpriteColl = 0u;
sim->spriteBgColl = 0u;
// $6920 cleared the latch, but the VIC goes on showing this frame
// through the jingle, so the first tick's read still sees it.
sim->prevFrameSpriteColl = frameSpriteCollisions(sim);
sim->rngT1 = 0x06u;
sim->rngT2 = 0x17u;
stFareTakeoffVoice(sim);
}
// $5EC4 + $4207 + $48AD -- a fresh game (or the attract demo).
void stSimNewGame(StSimT *sim, uint8_t playerCount, bool demo) {
uint8_t p;
uint8_t keepBuf[sizeof(sim->demoBuf)];
uint8_t keepParity = sim->flameParity;
uint8_t keepWave = sim->waveIdx;
uint8_t keepWalk = sim->walkParity;
// $5EC4 clears the game state but the playback buffer, the flame
// parity, the wave index and the walk parity all survive. So does
// the displayed picture -- screen RAM, color RAM and the charset
// are not game state, and the attract demo's "GET READY" banner is
// drawn over the still-live title screen -- so the clear starts at
// ST_SIM_CLEAR_FROM. Every level entry rebinds the image anyway
// (stSimEnterLevel), so nothing downstream sees the difference.
memcpy(keepBuf, sim->demoBuf, sizeof(keepBuf));
memset((uint8_t *)sim + ST_SIM_CLEAR_FROM, 0, sizeof(*sim) - ST_SIM_CLEAR_FROM);
memcpy(sim->demoBuf, keepBuf, sizeof(keepBuf));
sim->flameParity = keepParity;
sim->waveIdx = keepWave;
sim->walkParity = keepWalk;
sim->stage0Rng = 0x64u;
sim->decayReload = 3u;
sim->playerCount = playerCount;
sim->player = 0u;
sim->playersDone = 0u;
sim->levelState = 0u;
sim->demoMode = demo ? 1u : 0u;
sim->rngHost = 0x2545F491u;
for (p = 0u; p < ST_MAX_PLAYERS; p++) {
sim->cabs[p] = ST_CABS_PER_PLAYER;
memcpy(sim->scoreBackup[p], kHudTemplate, ST_NUMBER_CHARS);
memcpy(sim->fareBackup[p], kHudTemplate, ST_NUMBER_CHARS);
}
sim->rngT1 = 0x06u;
sim->rngT2 = 0x17u;
}
// $6B64..$6BCD -- the game's side of a finished wreck (the attract
// demo returns to the title instead): a fare aboard is lost -- its meter,
// its pads, an open hatch, its message -- then the player's cab count
// drops. With cabs left the host respawns the cab (stSimRespawn, $5F27).
StTickResultE stSimLoseCab(StSimT *sim) {
uint8_t p;
if (sim->stage == ST_STAGE_RIDING) {
stSimHudInit(sim);
if (sim->fareSlotCount != 0u) {
sim->spriteSlots[sim->activeDyingSlot] = 0u;
sim->fareSlotCount--;
if (sim->activeSpriteIdx == ST_FARE_DEST_UP) {
uint8_t k;
for (k = 0u; k < ST_TRANSPORTER_CELLS; k++) {
setCell(sim, (uint16_t)(ST_CELL_TRANSPORTER + k), ST_CHAR_TRANSPORTER);
}
} else {
sim->spriteSlots[sim->activeSpriteIdx] = 0u;
sim->fareSlotCount--;
}
}
sim->activeSpriteIdx = 0u;
sim->stage = ST_STAGE_IDLE;
stSimClearMessage(sim);
}
// $6BBA
p = sim->player;
sim->cabs[p]--;
if (sim->cabs[p] == 0u) {
return ST_TICK_PLAYER_OUT;
}
setCell(sim, (uint16_t)(ST_CELL_CAB_ICONS + sim->cabs[p]), ST_CHAR_BLANK);
return ST_TICK_LIFE_LOST;
}
// Everything must be repainted.
// A glyph's bits changed: the renderer has to repaint every cell showing
// that character. The list is short (one or two per frame), so a linear
// scan for duplicates is cheaper than any index; an overflow just says
// "all of them" and costs one full repaint.
void stSimMarkChar(StSimT *sim, uint8_t ch) {
uint8_t k;
if (sim->charDirtyAll) {
return;
}
for (k = 0u; k < sim->charDirtyCount; k++) {
if (sim->charDirtyList[k] == ch) {
return;
}
}
if (sim->charDirtyCount == ST_CHAR_DIRTY_MAX) {
sim->charDirtyAll = true;
return;
}
sim->charDirtyList[sim->charDirtyCount] = ch;
sim->charDirtyCount++;
}
// $4253 + $4293 -- snapshot the sprite shadows into the frame the VIC
// shows next. The title and level-intro loops flush the same way.
void stSimMarshal(StSimT *sim) {
uint8_t i;
uint8_t enable = 0u;
for (i = 0u; i < ST_HW_SPRITES; i++) {
sim->frame.x[i] = (uint16_t)(((uint16_t)(sim->spr[i].msb != 0u ? 1u : 0u) << 8) | sim->spr[i].col);
sim->frame.y[i] = sim->spr[i].row;
sim->frame.ptr[i] = sim->spr[i].ptr;
sim->frame.color[i] = sim->spr[i].color;
if (sim->spr[i].enable != 0u) {
enable |= kStBit[i];
}
}
sim->frame.enableMask = enable;
sim->frame.multiMask = sim->multiColorMask;
}
// Every cell repaints AND the glyph index is rebuilt: for callers that
// replaced the screen bytes wholesale (a level load, the title scene).
void stSimDirtyAll(StSimT *sim) {
stSimDirtyCells(sim);
// Every bulk screen write calls this, and those bypass setCell, so
// this is where the glyph reverse index gets re-derived.
glyphIndexRebuild(sim);
}
// Every cell repaints; the screen bytes are as they were, so the glyph
// index stands. A rebuild is ~0.15 s on the IIgs (1000 far-pointer
// list links), and the level-entry path used to pay it twice.
void stSimDirtyCells(StSimT *sim) {
memset(sim->cellDirty, 1, ST_SCREEN_CELLS);
sim->dirtyCount = 0u;
sim->dirtyAll = true;
}
// $6866 / $6877 -- the pad indicator cells beside the HUD.
void stSimPadLight(StSimT *sim, bool on) {
if (on) {
setColorCell(sim, ST_CELL(23, 28), 0x0Bu);
setColorCell(sim, ST_CELL(23, 29), 0x0Bu);
setColorCell(sim, ST_CELL(24, 28), 0x02u);
setColorCell(sim, ST_CELL(24, 29), 0x02u);
} else {
setColorCell(sim, ST_CELL(24, 28), 0x0Bu);
setColorCell(sim, ST_CELL(24, 29), 0x0Bu);
setColorCell(sim, ST_CELL(23, 28), 0x07u);
setColorCell(sim, ST_CELL(23, 29), 0x07u);
}
}
// $401B -- one character into screen RAM.
void stSimPutChar(StSimT *sim, uint8_t col, uint8_t row, uint8_t ch) {
setCell(sim, ST_CELL(row, col), ch);
}
// $401E -- one color into color RAM.
void stSimPutColor(StSimT *sim, uint8_t col, uint8_t row, uint8_t color) {
setColorCell(sim, ST_CELL(row, col), color);
}
// $4080 -- 1..n. The demo walks a 64-byte table so its rides replay
// exactly; a real game reads the SID noise oscillator, which a host
// LCG stands in for.
uint8_t stSimRng(StSimT *sim, uint8_t n) {
uint8_t r;
uint16_t product;
if (sim->demoMode != 0u) {
sim->rngT1 = (uint8_t)((sim->rngT1 + 1u) & 0x3Fu);
sim->rngT2++;
r = (uint8_t)(stC64RngByte(sim->rngT1) + sim->rngT2);
} else {
sim->rngHost = sim->rngHost * 1103515245u + 12345u;
r = (uint8_t)(sim->rngHost >> 16);
}
product = (uint16_t)((uint16_t)n * (uint16_t)r);
return (uint8_t)((product >> 8) + 1u);
}
// $63D0 -- rotate every row of a glyph one pixel right and mark every
// cell showing it for repaint: the transporter hatch and the level O
// electroids both animate this way.
void stSimRotateGlyph(StSimT *sim, uint8_t ch) {
uint8_t *rows = stSimGlyphMut(sim, ch);
uint8_t row;
for (row = 0u; row < 8u; row++) {
uint8_t b = rows[row];
rows[row] = (uint8_t)((b >> 1) | (b << 7));
}
stSimMarkChar(sim, ch);
}
// The score glyphs as pennies (for the high-score table).
uint32_t stSimScorePennies(const StSimT *sim) {
uint32_t v = 0u;
uint8_t k;
for (k = 0u; k < ST_NUMBER_CHARS; k++) {
if (k == 4u) {
continue;
}
v = v * 10u + validateDigit(sim->screen[ST_CELL_SCORE + k]);
}
return v;
}
// The boot-time content of the playback buffer.
void stSimSeedDemoBuffer(StSimT *sim, const uint8_t *image, uint16_t len) {
if (len > sizeof(sim->demoBuf)) {
len = (uint16_t)sizeof(sim->demoBuf);
}
memcpy(sim->demoBuf, image, len);
}
// $0902 / $4740 -- load a recording over the buffer and rewind.
void stSimSetDemoStream(StSimT *sim, const uint8_t *stream, uint16_t len) {
if (len > sizeof(sim->demoBuf)) {
len = (uint16_t)sizeof(sim->demoBuf);
}
memcpy(sim->demoBuf, stream, len);
sim->demoOff = 0u;
sim->demoTimer = sim->demoBuf[1];
}
// $42E9 -- an SFX program starts; voices 0 and 1 arm their release timer.
void stSimSfx(StSimT *sim, const uint8_t *program9) {
uint8_t voice = program9[ST_SFX_VOICE_AT];
if (voice < ST_SID_TIMED_VOICES) {
sim->sidRelTimer[voice] = program9[ST_SFX_RELEASE_AT];
}
stAudioSfx(program9);
}
// $411B -- add a signed byte to a sprite's 17-bit X, carrying into the
// msb shadow.
void stSimSpriteAddX(StSimT *sim, uint8_t idx, uint8_t delta) {
uint16_t x = (uint16_t)(stSimSpriteX(sim, idx) + (uint16_t)(int16_t)(int8_t)delta);
sim->spr[idx].col = (uint8_t)x;
sim->spr[idx].msb = (uint8_t)(x >> 8);
}
// Bitmap for a block pointer: the standard set, or the level's own.
const uint8_t *stSimSpriteBitmap(const StSimT *sim, uint8_t ptr) {
uint8_t k;
if (ptr >= ST_SPRITE_PTR_FIRST && ptr <= ST_SPRITE_PTR_LAST) {
return stC64SpriteBitmap((uint8_t)(ptr - ST_SPRITE_PTR_FIRST));
}
if (sim->level != 0) {
for (k = 0u; k < sim->level->spriteCount; k++) {
if (sim->level->sprites[k].ptr == ptr) {
return sim->level->sprites[k].bitmap;
}
}
}
return 0;
}
// The 17-bit VIC sprite X the shadow tables hold as msb:col.
uint16_t stSimSpriteX(const StSimT *sim, uint8_t idx) {
return (uint16_t)(((uint16_t)sim->spr[idx].msb << 8) | sim->spr[idx].col);
}
// $5F40 -- one iteration of the main loop.
StTickResultE stSimTick(StSimT *sim) {
StTickResultE result = ST_TICK_CONTINUE;
if (sim->collisionPhase == 0u) {
physicsTick(sim);
fireButtonEdge(sim);
stSimFlameUpdate(sim);
padDetect(sim);
taxiSpriteCelSelect(sim);
if (levelEndCheck(sim)) {
stAudioNoise(false);
voicesOff(sim);
stSimArchiveHud(sim);
return ST_TICK_LEVEL_EXIT;
}
padLandingBob(sim);
fuelTick(sim);
stFareEventVoice(sim);
}
stFarePostTickGate(sim);
stFareStageDispatch(sim);
stHookPerTick2(sim);
// $5F94: the frame drawn while the CPU waits shows the last flush's
// sprites over the picture as this tick has left it.
sim->prevFrameBgColl = frameBgCollisions(sim);
stSimMarshal(sim);
stSimRotateGlyph(sim, ST_CHAR_TRANSPORTER);
stHookPerTick3(sim);
fuelBarHud(sim);
if (sim->collisionPhase == 0u) {
collisionDispatch(sim);
} else if (sim->collisionPhase == 1u) {
computeCollisions(sim);
collisionPhase1(sim);
} else if (sim->collisionPhase == 2u) {
computeCollisions(sim);
collisionPhase2(sim);
} else {
computeCollisions(sim);
result = collisionPhase3(sim);
if (result != ST_TICK_CONTINUE) {
return result;
}
}
hudDraw(sim);
sfxEnvelopeTick(sim);
// $4FCB runStopWatcher: any joystick input ends the demo.
if (sim->demoMode != 0u && (sim->rawInput & 0x1Fu) != 0u) {
return ST_TICK_DEMO_INPUT;
}
passengerArrTick(sim);
return ST_TICK_CONTINUE;
}
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