[planeX dirX] [planeY dirY]And the inverse of a 2x2 matrix is very easy to calculate
____________1___________ [dirY dirX] (planeX*dirYdirX*planeY) * [planeY planeX]
#define screenWidth 640
#define screenHeight 480
#define texWidth 64
#define texHeight 64
#define mapWidth 24
#define mapHeight 24
int worldMap[mapWidth][mapHeight] =
{
{8,8,8,8,8,8,8,8,8,8,8,4,4,6,4,4,6,4,6,4,4,4,6,4},
{8,0,0,0,0,0,0,0,0,0,8,4,0,0,0,0,0,0,0,0,0,0,0,4},
{8,0,3,3,0,0,0,0,0,8,8,4,0,0,0,0,0,0,0,0,0,0,0,6},
{8,0,0,3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,6},
{8,0,3,3,0,0,0,0,0,8,8,4,0,0,0,0,0,0,0,0,0,0,0,4},
{8,0,0,0,0,0,0,0,0,0,8,4,0,0,0,0,0,6,6,6,0,6,4,6},
{8,8,8,8,0,8,8,8,8,8,8,4,4,4,4,4,4,6,0,0,0,0,0,6},
{7,7,7,7,0,7,7,7,7,0,8,0,8,0,8,0,8,4,0,4,0,6,0,6},
{7,7,0,0,0,0,0,0,7,8,0,8,0,8,0,8,8,6,0,0,0,0,0,6},
{7,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,8,6,0,0,0,0,0,4},
{7,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,8,6,0,6,0,6,0,6},
{7,7,0,0,0,0,0,0,7,8,0,8,0,8,0,8,8,6,4,6,0,6,6,6},
{7,7,7,7,0,7,7,7,7,8,8,4,0,6,8,4,8,3,3,3,0,3,3,3},
{2,2,2,2,0,2,2,2,2,4,6,4,0,0,6,0,6,3,0,0,0,0,0,3},
{2,2,0,0,0,0,0,2,2,4,0,0,0,0,0,0,4,3,0,0,0,0,0,3},
{2,0,0,0,0,0,0,0,2,4,0,0,0,0,0,0,4,3,0,0,0,0,0,3},
{1,0,0,0,0,0,0,0,1,4,4,4,4,4,6,0,6,3,3,0,0,0,3,3},
{2,0,0,0,0,0,0,0,2,2,2,1,2,2,2,6,6,0,0,5,0,5,0,5},
{2,2,0,0,0,0,0,2,2,2,0,0,0,2,2,0,5,0,5,0,0,0,5,5},
{2,0,0,0,0,0,0,0,2,0,0,0,0,0,2,5,0,5,0,5,0,5,0,5},
{1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,5},
{2,0,0,0,0,0,0,0,2,0,0,0,0,0,2,5,0,5,0,5,0,5,0,5},
{2,2,0,0,0,0,0,2,2,2,0,0,0,2,2,0,5,0,5,0,0,0,5,5},
{2,2,2,2,1,2,2,2,2,2,2,1,2,2,2,5,5,5,5,5,5,5,5,5}
};
struct Sprite
{
double x;
double y;
int texture;
};
#define numSprites 19
Sprite sprite[numSprites] =
{
{20.5, 11.5, 10}, //green light in front of playerstart
//green lights in every room
{18.5,4.5, 10},
{10.0,4.5, 10},
{10.0,12.5,10},
{3.5, 6.5, 10},
{3.5, 20.5,10},
{3.5, 14.5,10},
{14.5,20.5,10},
//row of pillars in front of wall: fisheye test
{18.5, 10.5, 9},
{18.5, 11.5, 9},
{18.5, 12.5, 9},
//some barrels around the map
{21.5, 1.5, 8},
{15.5, 1.5, 8},
{16.0, 1.8, 8},
{16.2, 1.2, 8},
{3.5, 2.5, 8},
{9.5, 15.5, 8},
{10.0, 15.1,8},
{10.5, 15.8,8},
};
Uint32 buffer[screenHeight][screenWidth]; // ycoordinate first because it works per scanline
//1D Zbuffer
double ZBuffer[screenWidth];
//arrays used to sort the sprites
int spriteOrder[numSprites];
double spriteDistance[numSprites];
//function used to sort the sprites
void combSort(int* order, double* dist, int amount);
int main(int /*argc*/, char */*argv*/[])
{
double posX = 22.0, posY = 11.5; //x and y start position
double dirX = 1.0, dirY = 0.0; //initial direction vector
double planeX = 0.0, planeY = 0.66; //the 2d raycaster version of camera plane
double time = 0; //time of current frame
double oldTime = 0; //time of previous frame
std::vector<Uint32> texture[11];
for(int i = 0; i < 11; i++) texture[i].resize(texWidth * texHeight);

screen(screenWidth,screenHeight, 0, "Raycaster");
//load some textures
unsigned long tw, th, error = 0;
error = loadImage(texture[0], tw, th, "pics/eagle.png");
error = loadImage(texture[1], tw, th, "pics/redbrick.png");
error = loadImage(texture[2], tw, th, "pics/purplestone.png");
error = loadImage(texture[3], tw, th, "pics/greystone.png");
error = loadImage(texture[4], tw, th, "pics/bluestone.png");
error = loadImage(texture[5], tw, th, "pics/mossy.png");
error = loadImage(texture[6], tw, th, "pics/wood.png");
error = loadImage(texture[7], tw, th, "pics/colorstone.png");
//load some sprite textures
error = loadImage(texture[8], tw, th, "pics/barrel.png");
error = loadImage(texture[9], tw, th, "pics/pillar.png");
error = loadImage(texture[10], tw, th, "pics/greenlight.png");
if(error) { std::cout << "error loading images" << std::endl; return 1; }

//start the main loop
while(!done())
{
for(int x = 0; x < w; x++)
{
//calculate ray position and direction
double cameraX = 2 * x / double(w)  1; //xcoordinate in camera space
double rayDirX = dirX + planeX * cameraX;
double rayDirY = dirY + planeY * cameraX;
//which box of the map we're in
int mapX = int(posX);
int mapY = int(posY);
//length of ray from current position to next x or yside
double sideDistX;
double sideDistY;
//length of ray from one x or yside to next x or yside
double deltaDistX = std::abs(1 / rayDirX);
double deltaDistY = std::abs(1 / rayDirY);
double perpWallDist;
//what direction to step in x or ydirection (either +1 or 1)
int stepX;
int stepY;
int hit = 0; //was there a wall hit?
int side; //was a NS or a EW wall hit?
//calculate step and initial sideDist
if (rayDirX < 0)
{
stepX = 1;
sideDistX = (posX  mapX) * deltaDistX;
}
else
{
stepX = 1;
sideDistX = (mapX + 1.0  posX) * deltaDistX;
}
if (rayDirY < 0)
{
stepY = 1;
sideDistY = (posY  mapY) * deltaDistY;
}
else
{
stepY = 1;
sideDistY = (mapY + 1.0  posY) * deltaDistY;
}
//perform DDA
while (hit == 0)
{
//jump to next map square, OR in xdirection, OR in ydirection
if (sideDistX < sideDistY)
{
sideDistX += deltaDistX;
mapX += stepX;
side = 0;
}
else
{
sideDistY += deltaDistY;
mapY += stepY;
side = 1;
}
//Check if ray has hit a wall
if (worldMap[mapX][mapY] > 0) hit = 1;
}
//Calculate distance of perpendicular ray (Euclidean distance will give fisheye effect!)
if (side == 0) perpWallDist = (mapX  posX + (1  stepX) / 2) / rayDirX;
else perpWallDist = (mapY  posY + (1  stepY) / 2) / rayDirY;
//Calculate height of line to draw on screen
int lineHeight = (int)(h / perpWallDist);
//calculate lowest and highest pixel to fill in current stripe
int drawStart = lineHeight / 2 + h / 2;
if(drawStart < 0) drawStart = 0;
int drawEnd = lineHeight / 2 + h / 2;
if(drawEnd >= h) drawEnd = h  1;
//texturing calculations
int texNum = worldMap[mapX][mapY]  1; //1 subtracted from it so that texture 0 can be used!
//calculate value of wallX
double wallX; //where exactly the wall was hit
if (side == 0) wallX = posY + perpWallDist * rayDirY;
else wallX = posX + perpWallDist * rayDirX;
wallX = floor((wallX));
//x coordinate on the texture
int texX = int(wallX * double(texWidth));
if(side == 0 && rayDirX > 0) texX = texWidth  texX  1;
if(side == 1 && rayDirY < 0) texX = texWidth  texX  1;
for(int y = drawStart; y < drawEnd; y++)
{
int d = y * 256  h * 128 + lineHeight * 128; //256 and 128 factors to avoid floats
// TODO: avoid the division to speed this up
int texY = ((d * texHeight) / lineHeight) / 256;
int color = texture[texNum][texWidth * texY + texX];
//make color darker for ysides: R, G and B byte each divided through two with a "shift" and an "and"
if(side == 1) color = (color >> 1) & 8355711;
buffer[y][x] = color;
}

//SET THE ZBUFFER FOR THE SPRITE CASTING
ZBuffer[x] = perpWallDist; //perpendicular distance is used
//FLOOR CASTING
double floorXWall, floorYWall; //x, y position of the floor texel at the bottom of the wall
//4 different wall directions possible
if(side == 0 && rayDirX > 0)
{
floorXWall = mapX;
floorYWall = mapY + wallX;
}
else if(side == 0 && rayDirX < 0)
{
floorXWall = mapX + 1.0;
floorYWall = mapY + wallX;
}
else if(side == 1 && rayDirY > 0)
{
floorXWall = mapX + wallX;
floorYWall = mapY;
}
else
{
floorXWall = mapX + wallX;
floorYWall = mapY + 1.0;
}
double distWall, distPlayer, currentDist;
distWall = perpWallDist;
distPlayer = 0.0;
if (drawEnd < 0) drawEnd = h; //becomes < 0 when the integer overflows
//draw the floor from drawEnd to the bottom of the screen
for(int y = drawEnd + 1; y < h; y++)
{
currentDist = h / (2.0 * y  h); //you could make a small lookup table for this instead
double weight = (currentDist  distPlayer) / (distWall  distPlayer);
double currentFloorX = weight * floorXWall + (1.0  weight) * posX;
double currentFloorY = weight * floorYWall + (1.0  weight) * posY;
int floorTexX, floorTexY;
floorTexX = int(currentFloorX * texWidth) % texWidth;
floorTexY = int(currentFloorY * texHeight) % texHeight;
//floor
buffer[y][x] = (texture[3][texWidth * floorTexY + floorTexX] >> 1) & 8355711;
//ceiling (symmetrical!)
buffer[h  y][x] = texture[6][texWidth * floorTexY + floorTexX];
}
}

//SPRITE CASTING
//sort sprites from far to close
for(int i = 0; i < numSprites; i++)
{
spriteOrder[i] = i;
spriteDistance[i] = ((posX  sprite[i].x) * (posX  sprite[i].x) + (posY  sprite[i].y) * (posY  sprite[i].y)); //sqrt not taken, unneeded
}
combSort(spriteOrder, spriteDistance, numSprites);
//after sorting the sprites, do the projection and draw them
for(int i = 0; i < numSprites; i++)
{
//translate sprite position to relative to camera
double spriteX = sprite[spriteOrder[i]].x  posX;
double spriteY = sprite[spriteOrder[i]].y  posY;
//transform sprite with the inverse camera matrix
// [ planeX dirX ] 1 [ dirY dirX ]
// [ ] = 1/(planeX*dirYdirX*planeY) * [ ]
// [ planeY dirY ] [ planeY planeX ]
double invDet = 1.0 / (planeX * dirY  dirX * planeY); //required for correct matrix multiplication
double transformX = invDet * (dirY * spriteX  dirX * spriteY);
double transformY = invDet * (planeY * spriteX + planeX * spriteY); //this is actually the depth inside the screen, that what Z is in 3D
int spriteScreenX = int((w / 2) * (1 + transformX / transformY));
//calculate height of the sprite on screen
int spriteHeight = abs(int(h / (transformY))); //using "transformY" instead of the real distance prevents fisheye
//calculate lowest and highest pixel to fill in current stripe
int drawStartY = spriteHeight / 2 + h / 2;
if(drawStartY < 0) drawStartY = 0;
int drawEndY = spriteHeight / 2 + h / 2;
if(drawEndY >= h) drawEndY = h  1;
//calculate width of the sprite
int spriteWidth = abs( int (h / (transformY)));
int drawStartX = spriteWidth / 2 + spriteScreenX;
if(drawStartX < 0) drawStartX = 0;
int drawEndX = spriteWidth / 2 + spriteScreenX;
if(drawEndX >= w) drawEndX = w  1;
//loop through every vertical stripe of the sprite on screen
for(int stripe = drawStartX; stripe < drawEndX; stripe++)
{
int texX = int(256 * (stripe  (spriteWidth / 2 + spriteScreenX)) * texWidth / spriteWidth) / 256;
//the conditions in the if are:
//1) it's in front of camera plane so you don't see things behind you
//2) it's on the screen (left)
//3) it's on the screen (right)
//4) ZBuffer, with perpendicular distance
if(transformY > 0 && stripe > 0 && stripe < w && transformY < ZBuffer[stripe])
for(int y = drawStartY; y < drawEndY; y++) //for every pixel of the current stripe
{
int d = (y) * 256  h * 128 + spriteHeight * 128; //256 and 128 factors to avoid floats
int texY = ((d * texHeight) / spriteHeight) / 256;
Uint32 color = texture[sprite[spriteOrder[i]].texture][texWidth * texY + texX]; //get current color from the texture
if((color & 0x00FFFFFF) != 0) buffer[y][stripe] = color; //paint pixel if it isn't black, black is the invisible color
}
}
}

drawBuffer(buffer[0]);
for(int x = 0; x < w; x++) for(int y = 0; y < h; y++) buffer[y][x] = 0; //clear the buffer instead of cls()
//timing for input and FPS counter
oldTime = time;
time = getTicks();
double frameTime = (time  oldTime) / 1000.0; //frametime is the time this frame has taken, in seconds
print(1.0 / frameTime); //FPS counter
redraw();
//speed modifiers
double moveSpeed = frameTime * 3.0; //the constant value is in squares/second
double rotSpeed = frameTime * 2.0; //the constant value is in radians/second
readKeys();
//move forward if no wall in front of you
if (keyDown(SDLK_UP))
{
if(worldMap[int(posX + dirX * moveSpeed)][int(posY)] == false) posX += dirX * moveSpeed;
if(worldMap[int(posX)][int(posY + dirY * moveSpeed)] == false) posY += dirY * moveSpeed;
}
//move backwards if no wall behind you
if (keyDown(SDLK_DOWN))
{
if(worldMap[int(posX  dirX * moveSpeed)][int(posY)] == false) posX = dirX * moveSpeed;
if(worldMap[int(posX)][int(posY  dirY * moveSpeed)] == false) posY = dirY * moveSpeed;
}
//rotate to the right
if (keyDown(SDLK_RIGHT))
{
//both camera direction and camera plane must be rotated
double oldDirX = dirX;
dirX = dirX * cos(rotSpeed)  dirY * sin(rotSpeed);
dirY = oldDirX * sin(rotSpeed) + dirY * cos(rotSpeed);
double oldPlaneX = planeX;
planeX = planeX * cos(rotSpeed)  planeY * sin(rotSpeed);
planeY = oldPlaneX * sin(rotSpeed) + planeY * cos(rotSpeed);
}
//rotate to the left
if (keyDown(SDLK_LEFT))
{
//both camera direction and camera plane must be rotated
double oldDirX = dirX;
dirX = dirX * cos(rotSpeed)  dirY * sin(rotSpeed);
dirY = oldDirX * sin(rotSpeed) + dirY * cos(rotSpeed);
double oldPlaneX = planeX;
planeX = planeX * cos(rotSpeed)  planeY * sin(rotSpeed);
planeY = oldPlaneX * sin(rotSpeed) + planeY * cos(rotSpeed);
}
}
}

//sort algorithm
void combSort(int* order, double* dist, int amount)
{
int gap = amount;
bool swapped = false;
while(gap > 1  swapped)
{
//shrink factor 1.3
gap = (gap * 10) / 13;
if(gap == 9  gap == 10) gap = 11;
if (gap < 1) gap = 1;
swapped = false;
for(int i = 0; i < amount  gap; i++)
{
int j = i + gap;
if(dist[i] < dist[j])
{
std::swap(dist[i], dist[j]);
std::swap(order[i], order[j]);
swapped = true;
}
}
}
}

//parameters for scaling and moving the sprites
#define uDiv 1
#define vDiv 1
#define vMove 0.0
int vMoveScreen = int(vMove / transformY);
//calculate height of the sprite on screen
int spriteHeight = abs(int(h / (transformY))) / vDiv; //using "transformY" instead of the real distance prevents fisheye
//calculate lowest and highest pixel to fill in current stripe
int drawStartY = spriteHeight / 2 + h / 2 + vMoveScreen;
if(drawStartY < 0) drawStartY = 0;
int drawEndY = spriteHeight / 2 + h / 2 + vMoveScreen;
if(drawEndY >= h) drawEndY = h  1;
//calculate width of the sprite
int spriteWidth = abs( int (h / (transformY))) / uDiv;
int drawStartX = spriteWidth / 2 + spriteScreenX;
if(drawStartX < 0) drawStartX = 0;
int drawEndX = spriteWidth / 2 + spriteScreenX;
if(drawEndX >= w) drawEndX = w  1;
//loop through every vertical stripe of the sprite on screen
for(int stripe = drawStartX; stripe < drawEndX; stripe++)
{
int texX = int(256 * (stripe  (spriteWidth / 2 + spriteScreenX)) * texWidth / spriteWidth) / 256;
//the conditions in the if are:
//1) it's in front of camera plane so you don't see things behind you
//2) it's on the screen (left)
//3) it's on the screen (right)
//4) ZBuffer, with perpendicular distance
if(transformY > 0 && stripe > 0 && stripe < w && transformY < ZBuffer[stripe])
for(int y = drawStartY; y < drawEndY; y++) //for every pixel of the current stripe
{
int d = (yvMoveScreen) * 256  h * 128 + spriteHeight * 128; //256 and 128 factors to avoid floats
int texY = ((d * texHeight) / spriteHeight) / 256;
Uint32 color = texture[sprite[spriteOrder[i]].texture][texWidth * texY + texX]; //get current color from the texture
if((color & 0x00FFFFFF) != 0) buffer[y][stripe] = color; //paint pixel if it isn't black, black is the invisible color
}
}
}

if((color & 0x00FFFFFF) != 0) buffer[y][stripe] = color; //paint pixel if it isn't black, black is the invisible color

if((color & 0x00FFFFFF) != 0) buffer[y][stripe] = RGBtoINT(INTtoRGB(buffer[y][stripe]) / 2 + INTtoRGB(color) / 2); //paint pixel if it isn't black, black is the invisible color

if((color & 0x00FFFFFF) != 0) buffer[y][stripe] = RGBtoINT(3 * INTtoRGB(buffer[y][stripe]) / 4 + INTtoRGB(color) / 4); //paint pixel if it isn't black, black is the invisible color

if((color & 0x00FFFFFF) != 0) buffer[y][stripe] = RGBtoINT((RGB_White  INTtoRGB(buffer[y][stripe])) / 2 + INTtoRGB(color) / 2); //paint pixel if it isn't black, black is the invisible color
