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main.c
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main.c
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#include <SDL2/SDL.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
typedef struct
{
float x;
float y;
}
Point;
typedef struct
{
int tile;
Point where;
}
Hit;
typedef struct
{
Point a;
Point b;
}
Line;
typedef struct
{
SDL_Window* window;
SDL_Renderer* renderer;
SDL_Texture* texture;
int xres;
int yres;
}
Gpu;
typedef struct
{
uint32_t* pixels;
int width;
}
Display;
typedef struct
{
int top;
int bot;
float size;
}
Wall;
typedef struct
{
Line fov;
Point where;
Point velocity;
float speed;
float acceleration;
float theta;
}
Hero;
typedef struct
{
const char** ceiling;
const char** walling;
const char** floring;
}
Map;
// Rotates the player by some radian value.
static Point turn(const Point a, const float t)
{
const Point b = { a.x * cosf(t) - a.y * sinf(t), a.x * sinf(t) + a.y * cosf(t) };
return b;
}
// Rotates a point 90 degrees.
static Point rag(const Point a)
{
const Point b = { -a.y, a.x };
return b;
}
// Subtracts two points.
static Point sub(const Point a, const Point b)
{
const Point c = { a.x - b.x, a.y - b.y };
return c;
}
// Adds two points.
static Point add(const Point a, const Point b)
{
const Point c = { a.x + b.x, a.y + b.y };
return c;
}
// Multiplies a point by a scalar value.
static Point mul(const Point a, const float n)
{
const Point b = { a.x * n, a.y * n };
return b;
}
// Returns the magnitude of a point.
static float mag(const Point a)
{
return sqrtf(a.x * a.x + a.y * a.y);
}
// Returns the unit vector of a point.
static Point unit(const Point a)
{
return mul(a, 1.0f / mag(a));
}
// Returns the slope of a point.
static float slope(const Point a)
{
return a.y / a.x;
}
// Fast floor (math.h is too slow).
static int fl(const float x)
{
return (int) x - (x < (int) x);
}
// Fast ceil (math.h is too slow).
static int cl(const float x)
{
return (int) x + (x > (int) x);
}
// Steps horizontally along a square grid.
static Point sh(const Point a, const Point b)
{
const float x = b.x > 0.0f ? fl(a.x + 1.0f) : cl(a.x - 1.0f);
const float y = slope(b) * (x - a.x) + a.y;
const Point c = { x, y };
return c;
}
// Steps vertically along a square grid.
static Point sv(const Point a, const Point b)
{
const float y = b.y > 0.0f ? fl(a.y + 1.0f) : cl(a.y - 1.0f);
const float x = (y - a.y) / slope(b) + a.x;
const Point c = { x, y };
return c;
}
// Returns a decimal value of the ascii tile value on the map.
static int tile(const Point a, const char** const tiles)
{
const int x = a.x;
const int y = a.y;
return tiles[y][x] - '0';
}
// Floating point decimal.
static float dec(const float x)
{
return x - (int) x;
}
// Casts a ray from <where> in unit <direction> until a <walling> tile is hit.
static Hit cast(const Point where, const Point direction, const char** const walling)
{
// Determine whether to step horizontally or vertically on the grid.
const Point hor = sh(where, direction);
const Point ver = sv(where, direction);
const Point ray = mag(sub(hor, where)) < mag(sub(ver, where)) ? hor : ver;
// Due to floating point error, the step may not make it to the next grid square.
// Three directions (dy, dx, dc) of a tiny step will be added to the ray
// depending on if the ray hit a horizontal wall, a vertical wall, or the corner
// of two walls, respectively.
const Point dc = mul(direction, 0.01f);
const Point dx = { dc.x, 0.0f };
const Point dy = { 0.0f, dc.y };
const Point test = add(ray,
// Tiny step for corner of two grid squares.
mag(sub(hor, ver)) < 1e-3f ? dc :
// Tiny step for vertical grid square.
dec(ray.x) == 0.0f ? dx :
// Tiny step for a horizontal grid square.
dy);
const Hit hit = { tile(test, walling), ray };
// If a wall was not hit, then continue advancing the ray.
return hit.tile ? hit : cast(ray, direction, walling);
}
// Party casting. Returns a percentage of <y> related to <yres> for ceiling and
// floor casting when lerping the floor or ceiling.
static float pcast(const float size, const int yres, const int y)
{
return size / (2 * (y + 1) - yres);
}
// Rotates a line by some radian amount.
static Line rotate(const Line l, const float t)
{
const Line line = { turn(l.a, t), turn(l.b, t) };
return line;
}
// Linear interpolation.
static Point lerp(const Line l, const float n)
{
return add(l.a, mul(sub(l.b, l.a), n));
}
// Setups the software gpu.
static Gpu setup(const int xres, const int yres, const bool vsync)
{
if (SDL_Init(SDL_INIT_VIDEO) != 0)
{
puts(SDL_GetError());
exit(1);
}
SDL_Window* const window = SDL_CreateWindow(
"littlewolf",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
xres, yres,
SDL_WINDOW_SHOWN);
SDL_Renderer* const renderer = SDL_CreateRenderer(
window,
-1,
SDL_RENDERER_ACCELERATED | (vsync ? SDL_RENDERER_PRESENTVSYNC : 0x0));
// Notice the flip between xres and yres.
// The texture is 90 degrees flipped on its side for fast cache access.
SDL_Texture* const texture = SDL_CreateTexture(
renderer,
SDL_PIXELFORMAT_ARGB8888,
SDL_TEXTUREACCESS_STREAMING,
yres, xres);
if(window == NULL || renderer == NULL || texture == NULL)
{
puts(SDL_GetError());
exit(1);
}
const Gpu gpu = { window, renderer, texture, xres, yres };
return gpu;
}
// Presents the software gpu to the window.
// Calls the real GPU to rotate texture back 90 degrees before presenting.
static void present(const Gpu gpu)
{
const SDL_Rect dst = {
(gpu.xres - gpu.yres) / 2,
(gpu.yres - gpu.xres) / 2,
gpu.yres, gpu.xres,
};
SDL_RenderCopyEx(gpu.renderer, gpu.texture, NULL, &dst, -90, NULL, SDL_FLIP_NONE);
SDL_RenderPresent(gpu.renderer);
}
// Locks the gpu, returning a pointer to video memory.
static Display lock(const Gpu gpu)
{
void* screen;
int pitch;
SDL_LockTexture(gpu.texture, NULL, &screen, &pitch);
const Display display = { (uint32_t*) screen, pitch / (int) sizeof(uint32_t) };
return display;
}
// Places a pixels in gpu video memory.
static void put(const Display display, const int x, const int y, const uint32_t pixel)
{
display.pixels[y + x * display.width] = pixel;
}
// Unlocks the gpu, making the pointer to video memory ready for presentation
static void unlock(const Gpu gpu)
{
SDL_UnlockTexture(gpu.texture);
}
// Spins the hero when keys h,l are held down.
static Hero spin(Hero hero, const uint8_t* key)
{
if(key[SDL_SCANCODE_H]) hero.theta -= 0.1f;
if(key[SDL_SCANCODE_L]) hero.theta += 0.1f;
return hero;
}
// Moves the hero when w,a,s,d are held down. Handles collision detection for the walls.
static Hero move(Hero hero, const char** const walling, const uint8_t* key)
{
const Point last = hero.where, zero = { 0.0f, 0.0f };
// Accelerates with key held down.
if(key[SDL_SCANCODE_W] || key[SDL_SCANCODE_S] || key[SDL_SCANCODE_D] || key[SDL_SCANCODE_A])
{
const Point reference = { 1.0f, 0.0f };
const Point direction = turn(reference, hero.theta);
const Point acceleration = mul(direction, hero.acceleration);
if(key[SDL_SCANCODE_W]) hero.velocity = add(hero.velocity, acceleration);
if(key[SDL_SCANCODE_S]) hero.velocity = sub(hero.velocity, acceleration);
if(key[SDL_SCANCODE_D]) hero.velocity = add(hero.velocity, rag(acceleration));
if(key[SDL_SCANCODE_A]) hero.velocity = sub(hero.velocity, rag(acceleration));
}
// Otherwise, decelerates (exponential decay).
else hero.velocity = mul(hero.velocity, 1.0f - hero.acceleration / hero.speed);
// Caps velocity if top speed is exceeded.
if(mag(hero.velocity) > hero.speed) hero.velocity = mul(unit(hero.velocity), hero.speed);
// Moves.
hero.where = add(hero.where, hero.velocity);
// Sets velocity to zero if there is a collision and puts hero back in bounds.
if(tile(hero.where, walling))
{
hero.velocity = zero;
hero.where = last;
}
return hero;
}
// Returns a color value (RGB) from a decimal tile value.
static uint32_t color(const int tile)
{
switch(tile)
{
default:
case 1: return 0x00AA0000; // Red.
case 2: return 0x0000AA00; // Green.
case 3: return 0x000000AA; // Blue.
}
}
// Calculates wall size using the <corrected> ray to the wall.
static Wall project(const int xres, const int yres, const float focal, const Point corrected)
{
// Normal distance of corrected ray is clamped to some small value else wall size will shoot to infinity.
const float normal = corrected.x < 1e-2f ? 1e-2f : corrected.x;
const float size = 0.5f * focal * xres / normal;
const int top = (yres + size) / 2.0f;
const int bot = (yres - size) / 2.0f;
// Top and bottom values are clamped to screen size else renderer will waste cycles
// (or segfault) when rasterizing pixels off screen.
const Wall wall = { top > yres ? yres : top, bot < 0 ? 0 : bot, size };
return wall;
}
// Renders the entire scene from the <hero> perspective given a <map> and a software <gpu>.
static void render(const Hero hero, const Map map, const Gpu gpu)
{
const int t0 = SDL_GetTicks();
const Line camera = rotate(hero.fov, hero.theta);
const Display display = lock(gpu);
// Ray cast for all columns of the window.
for(int x = 0; x < gpu.xres; x++)
{
const Point direction = lerp(camera, x / (float) gpu.xres);
const Hit hit = cast(hero.where, direction, map.walling);
const Point ray = sub(hit.where, hero.where);
const Line trace = { hero.where, hit.where };
const Point corrected = turn(ray, -hero.theta);
const Wall wall = project(gpu.xres, gpu.yres, hero.fov.a.x, corrected);
// Renders flooring.
for(int y = 0; y < wall.bot; y++)
put(display, x, y, color(tile(lerp(trace, -pcast(wall.size, gpu.yres, y)), map.floring)));
// Renders wall.
for(int y = wall.bot; y < wall.top; y++)
put(display, x, y, color(hit.tile));
// Renders ceiling.
for(int y = wall.top; y < gpu.yres; y++)
put(display, x, y, color(tile(lerp(trace, +pcast(wall.size, gpu.yres, y)), map.ceiling)));
}
unlock(gpu);
present(gpu);
// Caps frame rate to ~60 fps if the vertical sync (VSYNC) init failed.
const int t1 = SDL_GetTicks();
const int ms = 16 - (t1 - t0);
SDL_Delay(ms < 0 ? 0 : ms);
}
static bool done()
{
SDL_Event event;
SDL_PollEvent(&event);
return event.type == SDL_QUIT
|| event.key.keysym.sym == SDLK_END
|| event.key.keysym.sym == SDLK_ESCAPE;
}
// Changes the field of view. A focal value of 1.0 is 90 degrees.
static Line viewport(const float focal)
{
const Line fov = {
{ focal, -1.0f },
{ focal, +1.0f },
};
return fov;
}
static Hero born(const float focal)
{
const Hero hero = {
viewport(focal),
// Where.
{ 3.5f, 3.5f },
// Velocity.
{ 0.0f, 0.0f },
// Speed.
0.10f,
// Acceleration.
0.015f,
// Theta radians.
0.0f
};
return hero;
}
// Builds the map. Note the static prefix for the parties. Map lives in .bss in private.
static Map build()
{
static const char* ceiling[] = {
"111111111111111111111111111111111111111111111",
"122223223232232111111111111111222232232322321",
"122222221111232111111111111111222222211112321",
"122221221232323232323232323232222212212323231",
"122222221111232111111111111111222222211112321",
"122223223232232111111111111111222232232322321",
"111111111111111111111111111111111111111111111",
};
static const char* walling[] = {
"111111111111111111111111111111111111111111111",
"100000000000000111111111111111000000000000001",
"103330001111000111111111111111033300011110001",
"103000000000000000000000000000030000030000001",
"103330001111000111111111111111033300011110001",
"100000000000000111111111111111000000000000001",
"111111111111111111111111111111111111111111111",
};
static const char* floring[] = {
"111111111111111111111111111111111111111111111",
"122223223232232111111111111111222232232322321",
"122222221111232111111111111111222222211112321",
"122222221232323323232323232323222222212323231",
"122222221111232111111111111111222222211112321",
"122223223232232111111111111111222232232322321",
"111111111111111111111111111111111111111111111",
};
const Map map = { ceiling, walling, floring };
return map;
}
// Get Psyched!
int main(int argc, char* argv[])
{
(void) argc;
(void) argv;
const Gpu gpu = setup(700, 400, true);
const Map map = build();
Hero hero = born(0.8f);
while(!done())
{
const uint8_t* key = SDL_GetKeyboardState(NULL);
hero = spin(hero, key);
hero = move(hero, map.walling, key);
render(hero, map, gpu);
}
// No need to free anything - gives quick exit.
return 0;
}