raycaster/raycaster.c

#include <stdio.h>
#include <stdlib.h>
#include <GLUT/glut.h>
#include <math.h>
#define PI 3.1415926535f
#define PI2 PI / 2
#define PI3 3 * PI / 2
#define DR 0.0174533f // One degree in radians

#define gameWidth 320
#define gameHeight 160

#define GAP 20

#define MAP_WIDTH (mapX * mapSize)
#define MAP_HEIGHT (mapY * mapSize)
#define TOTAL_WIDTH (MAP_WIDTH + GAP + gameWidth)
#define TOTAL_HEIGHT (MAP_HEIGHT > gameHeight ? MAP_HEIGHT : gameHeight)

// 0°    => 0    radians  (RIGHT)
// 90°   => π/2  radians  (TOP)
// 180°  => π    radians  (LEFT)
// 270°  => 3π/2 radians  (BOTTOM)
// 360°  => 2π   radians  (RIGHT)

// * Player position (playerX, playerY), delta (playerDeltaX, playerDeltaY), and angle (pa)
float playerX, playerY, playerDeltaX, playerDeltaY, playerAngle;

// * Draw the player on the screen
void drawPlayer()
{
  // Draws the player square
  glColor3f(1, 1, 0);
  glPointSize(8);
  glBegin(GL_POINTS);
  glVertex2i(playerX, playerY);
  glEnd();

  // Draws the player direction
  glLineWidth(3);
  glBegin(GL_LINES);
  glVertex2i(playerX, playerY);
  glVertex2i(playerX + playerDeltaX * 5, playerY + playerDeltaY * 5);
  glEnd();
}

// * Define the world
int mapX = 8, mapY = 8, mapSize = 64;

// clang-format off
int map[] =
{
   1,1,1,1,1,1,1,1,
   1,0,1,0,0,0,0,1,
   1,0,1,0,0,0,0,1,
   1,0,1,0,0,0,0,1,
   1,0,0,0,0,0,0,1,
   1,0,0,0,0,2,0,1,
   1,0,0,0,0,0,0,1,
   1,1,1,1,1,1,1,1,
};
// clang-format on

// * Draws the top-down map with white alls and black floors
void drawMap2D()
{
  int x, y, xo, yo;
  for (y = 0; y < mapY; y++)
  {
    for (x = 0; x < mapX; x++)
    {
      // Check if it's a wall
      if (map[y * mapX + x] > 0)
      {
        // Color walls (white)
        glColor3f(1, 1, 1);
      }
      else
      {
        // Color floors (black)
        glColor3f(0, 0, 0);
      }

      xo = x * mapSize;
      yo = y * mapSize;
      glBegin(GL_QUADS);

      // Draw each block; the +-1 creates the outline
      glVertex2i(xo + 1, yo + 1);
      glVertex2i(xo + 1, yo + mapSize - 1);
      glVertex2i(xo + mapSize - 1, yo + mapSize - 1);
      glVertex2i(xo + mapSize - 1, yo + 1);
      glEnd();
    }
  }
}

// * Returns the distance between the player and the ray's endpoint
// That's the hypotenuse, so we can use the Pythagorean theorem.
float dist(float ax, float ay, float bx, float by, float ang)
{
  // SOH - CAH - TOA
  return (sqrt((bx - ax) * (bx - ax) + (by - ay) * (by - ay)));
}

// * The actual raycaster
void drawRays3D()
{
  int r, mx, my, mapPoint, dof;

  // Ray x, y, angle
  float rayX, rayY, rayAngle;

  float xo, yo;

  // Final distance
  float disT;

  // Let's initialize the ray angle n degrees from the player's facing position
  // ra = ray angle; pa = player angle; DR = degree radian; n = degrees to use
  rayAngle = playerAngle - DR * 30;

  // Make sure to limit the next angle
  if (rayAngle < 0)
  {
    rayAngle += 2 * PI;
  }
  if (rayAngle > 2 * PI)
  {
    rayAngle -= 2 * PI;
  }

  // * Cast n rays
  for (r = 0; r < 60; r++)
  {
    // * --- Check Horizontal Lines ---
    dof = 0;

    // We need to get the shortest ray cast in either the vertical or horizontal
    // distance. So, we'll set a default that's way higher than we'll ever
    // calculate, and save the horizontal ray's X and Y position.
    float distanceHor = 1000000, hx = playerX, hy = playerY;

    // Negative inverse of tangent
    float aTan = -1.0f / tanf(rayAngle);

    // Check if the ray is looking up or down.
    // If it's less than π (e.g., 180°), we're looking down.

    // ? Looking up (ray angle > π)
    if (rayAngle > PI)
    {
      // Round the ray's Y position to the nearest 64th value.
      // We can do this by bit-shifting down by 6, then bit-shifting back up by
      // 6. Then, we subtract a small amount for accuracy.
      rayY = (((int)playerY >> 6) << 6) - 0.0001f;

      // The ray's X value is the distance between the player and the ray's Y
      // position, times the inverse of tangent, plus the player's X position.
      rayX = (playerY - rayY) * aTan + playerX;

      // Now that we have the ray's first grid intersection position, we need
      // the next X and Y offset for the second grid intersection point.
      yo = -64;
      xo = -yo * aTan;
    }

    // ? Looking down
    if (rayAngle < PI)
    {
      // This is almost exactly the same as looking up, but we add one grid
      // unit, instead of subtracting a tiny amount.
      rayY = (((int)playerY >> 6) << 6) + 64;

      rayX = (playerY - rayY) * aTan + playerX;

      // This is almost exactly the same as looking up, but we add instead of
      // subtract.
      yo = 64;
      xo = -yo * aTan;
    }

    // ? Looking straight left or right
    if (rayAngle == 0.0f || rayAngle == PI)
    {
      // It's impossible to ever hit a horizontal line
      rayX = playerX;
      rayY = playerY;
    }

    int mv = 0, mh = 0;

    // ? We don't want to get caught in an infinite loop, so use the
    // depth-of-field to limit our check to a max of 8.
    while (dof < 8)
    {
      // We know the coordinates where the ray will hit the wall, but we need
      // to know where that is in the map array.
      // Let's take the ray hit position (rx,ry) and divide it by 64 (bit-shift
      // 6 places), and use that to find the position in the map's array.
      mx = (int)(rayX) >> 6;
      my = (int)(rayY) >> 6;
      mapPoint = my * mapX + mx;

      // If the map position is less than the array's size, then we can check it
      // inside the map. If the value is 1, there's a wall. If we hit a wall,
      // we're done!
      if (mapPoint > 0 && mapPoint < mapX * mapY && map[mapPoint] > 0)
      {
        // We hit a wall!

        mh = map[mapPoint];

        // Save the values and calculate the distance from the player
        hx = rayX;
        hy = rayY;
        distanceHor = dist(playerX, playerY, hx, hy, rayAngle);

        dof = 8; // Break the loop - no need to calculate more.
      }
      else
      {
        // If we didn't hit a wall, we check the next horizontal line by adding
        // the x and y offset.
        rayX += xo;
        rayY += yo;
        dof += 1;
      }
    }

    // * --- Check Vertical Lines ---
    dof = 0;
    float distanceVert = 1000000, vx = playerX, vy = playerY;

    // Negative of tangent
    float nTan = -tanf(rayAngle);

    // ? Looking left
    if (rayAngle > PI2 && rayAngle < PI3)
    {
      rayX = (((int)playerX >> 6) << 6) - 0.0001f;
      rayY = (playerX - rayX) * nTan + playerY;
      xo = -64;
      yo = -xo * nTan;
    }

    // ? Looking right
    if (rayAngle < PI2 || rayAngle > PI3)
    {
      rayX = (((int)playerX >> 6) << 6) + 64;
      rayY = (playerX - rayX) * nTan + playerY;
      xo = 64;
      yo = -xo * nTan;
    }

    // ? Looking straight up or down
    if (rayAngle == 0.0f || rayAngle == PI)
    {
      rayX = playerX;
      rayY = playerY;
    }

    while (dof < 8)
    {
      // We know the coordinates where the ray will hit the wall, but we need
      // to know where that is in the map array.
      // Let's take the ray hit position (rx,ry) and divide it by 64 (bit-shift
      // 6 places), and use that to find the position in the map's array.
      mx = (int)(rayX) >> 6;
      my = (int)(rayY) >> 6;
      mapPoint = my * mapX + mx;

      // If the map position is less than the array's size, then we can check it
      // inside the map. If the value is 1, there's a wall. If we hit a wall,
      // we're done!
      if (mapPoint > 0 && mapPoint < mapX * mapY && map[mapPoint] > 0)
      {
        // We hit a wall!

        mv = map[mapPoint];

        // Save the values and calculate the distance from the player
        vx = rayX;
        vy = rayY;
        distanceVert = dist(playerX, playerY, vx, vy, rayAngle);

        dof = 8; // Break the loop - no need to calculate more.
      }
      else
      {
        // If we didn't hit a wall, we check the next horizontal line by adding
        // the x and y offset.
        rayX += xo;
        rayY += yo;
        dof += 1;
      }
    }

    // * Compare shortest horizontal and vertical line, then use the shortest
    // This is what actually determines our ray that hits a wall!

    // Vertical wall hit
    if (distanceVert < distanceHor)
    {
      rayX = vx;
      rayY = vy;
      disT = distanceVert;
      // Vertical walls are drawn a little brighter than horizontal walls
      glColor3f(0.9, 0, 0);

      if (mv == 2)
      {
        glColor3f(0, 0, 0.7);
      }
    }

    // Horizontal wall hit
    if (distanceHor < distanceVert)
    {
      rayX = hx;
      rayY = hy;
      disT = distanceHor;
      // Horizontal walls are drawn a little darker than vertical walls
      glColor3f(0.7, 0, 0);

      if (mh == 2)
      {
        glColor3f(0, 0, 0.4);
      }
    }

    // * Draw the ray
    glLineWidth(3);
    glBegin(GL_LINES);
    glVertex2i(playerX, playerY);
    glVertex2i(rayX, rayY);
    glEnd();

    // * --- Draw 3D Walls ---

    // Correct the fish-eye effect
    float correctedAngle = playerAngle - rayAngle;
    if (correctedAngle < 0)
    {
      correctedAngle += 2 * PI;
    }
    if (correctedAngle > 2 * PI)
    {
      correctedAngle -= 2 * PI;
    }

    disT = disT * cos(correctedAngle);

    // The formula for each line height will be the cube size (64) times our
    // screen height, divided by the ray distance (disT).
    // The further away, the larger the distance and the shorter the final line
    // height will be.
    float lineHeight = (mapSize * gameHeight) / disT;
    if (lineHeight > gameHeight)
    {
      lineHeight = gameHeight;
    }

    // Let's make sure the line doesn't exceed our vertical space, so we cap it
    if (lineHeight > gameWidth)
    {
      lineHeight = gameWidth;
    }

    // We need to offset the line to the middle of the screen
    // That's the full window height, minus half the line height
    float lineOffset = (gameHeight / 2.0f) - (lineHeight / 2.0f);

    // Calculate dynamic column width and horizontal starting offset
    float rayWidth = (float)gameWidth / 60.0f;
    float rayX3D = MAP_WIDTH + GAP + (r * rayWidth);

    // * Draw the "wall" line
    // Draw solid wall column using QUADS instead of GL_LINES
    glBegin(GL_QUADS);
    glVertex2f(rayX3D, lineOffset);
    glVertex2f(rayX3D + rayWidth, lineOffset);
    glVertex2f(rayX3D + rayWidth, lineOffset + lineHeight);
    glVertex2f(rayX3D, lineOffset + lineHeight);
    glEnd();

    // * Increase the ray angle to draw the next ray
    rayAngle += DR;
    if (rayAngle < 0)
    {
      rayAngle += 2 * PI;
    }
    if (rayAngle > 2 * PI)
    {
      rayAngle -= 2 * PI;
    }
  }
}

// * Draw ceiling
void drawCeiling()
{
  float halfHeight = (float)(gameHeight / 2);

  glBegin(GL_QUADS);
  for (float distance = 0; distance < halfHeight; distance += 1.0f)
  {
    // Normalize color from 0.0 to 1.0 based on distance, multiplied by relative intensity
    float colorIntensity = 0.5f + (distance / halfHeight);
    glColor3f(0.25 * colorIntensity, 0.25 * colorIntensity, 0.25 * colorIntensity);

    // Draw a horizontal strip at the current distance
    glVertex2f(MAP_WIDTH + GAP, distance);
    glVertex2f(MAP_WIDTH + GAP, distance + 1.0f);
    glVertex2f(TOTAL_WIDTH, distance + 1.0f);
    glVertex2f(TOTAL_WIDTH, distance);
  }
  glEnd();
}

// * Draw floor
void drawFloor()
{
  float halfHeight = (float)(gameHeight / 2);

  glBegin(GL_QUADS);
  for (float distance = 0; distance < halfHeight; distance += 1.0f)
  {

    float colorIntensity = 0.5f + (distance / halfHeight);
    glColor3f(0.25 * colorIntensity, 0.25 * colorIntensity, 0.0f);

    float y = halfHeight + distance;
    glVertex2f(MAP_WIDTH + GAP, y);
    glVertex2f(MAP_WIDTH + GAP, y + 1.0f);
    glVertex2f(TOTAL_WIDTH, y + 1.0f);
    glVertex2f(TOTAL_WIDTH, y);
  }
  glEnd();
}

// * Main rendering
void display()
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  drawCeiling();
  drawFloor();
  drawMap2D();
  drawRays3D();
  drawPlayer();

  glutSwapBuffers();
}

// * Check for key presses and move the "player" accordingly
void buttons(unsigned char key, int x, int y)
{
  // ? Move left
  if (key == 'a')
  {
    // We change the angle by a small value because we're not working with
    // degrees. In C, we instead use radians, which is 0 -> 2π.
    //
    // 0° -> 360° ≈ 0 -> ~6.28

    // Change player angle slightly (using radians)
    playerAngle -= 0.1;

    // If player angle drops below 0, let's reset back to 2π
    if (playerAngle < 0)
    {
      playerAngle += 2 * PI;
    }

    // The values returned from sin() and cos() are very small, so we'll just
    // artificialy inflate them by multilying by 5. This is our actual movement.
    playerDeltaX = cos(playerAngle) * 5.0f;
    playerDeltaY = sin(playerAngle) * 5.0f;
  }

  // ? Move right
  if (key == 'd')
  {
    playerAngle += 0.1;

    if (playerAngle > 2 * PI)
    {
      playerAngle -= 2 * PI;
    }

    playerDeltaX = cos(playerAngle) * 5.0f;
    playerDeltaY = sin(playerAngle) * 5.0f;
  }

  // ? Move forward
  if (key == 'w')
  {
    // We change the X and Y values based on our delta, which is calculated
    // during our rotation.
    playerX += playerDeltaX;
    playerY += playerDeltaY;
  }

  // ? Move backwards
  if (key == 's')
  {
    playerX -= playerDeltaX;
    playerY -= playerDeltaY;
  }
  glutPostRedisplay();
}

void init()
{
  // Sets the screen to the given color (grey)
  glClearColor(0.3, 0.3, 0.3, 0);

  // Sets the window to be 2D at a given size
  // gluOrtho2D(0, 1024, 512, 0);
  gluOrtho2D(0, TOTAL_WIDTH, TOTAL_HEIGHT, 0);

  // Spawn player centered in grid tile (1, 1)
  playerX = 1.5f * mapSize;
  playerY = 1.5f * mapSize;

  playerAngle = 0;

  // Calculate the initial player deltaX and deltaY
  playerDeltaX = cos(playerAngle) * 5.0f;
  playerDeltaY = sin(playerAngle) * 5.0f;
}

int main(int argc, char *argv[])
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
  glutInitWindowSize(TOTAL_WIDTH, TOTAL_HEIGHT);
  glutCreateWindow("Raycaster");

  init();

  // Send display parameters to the display function
  glutDisplayFunc(display);

  // Send key presses to the keyboard function
  glutKeyboardFunc(buttons);

  glutMainLoop();
}