The following C++ function does line-of-sight testing for a 2D game that uses tiles. The level map is a multidimensional array of integers (levelmap[LEVEL_HEIGHT][LEVEL_WIDTH]) that represent each tile; 0 signifies and empty tile, any number higher than that is solid. A vector2 is just a datatype that contains an object's x and y position.

// Check line of sight between two points (usually the camera/player)
// Based on Bresenham's line algorithm
// Returns true if line of sight is achieved
bool CheckLine(sf::Int8 levelmap[LEVEL_HEIGHT][LEVEL_WIDTH], sf::Vector2f A, float rotationA, sf::Vector2f B) const
{
    // Make sure A is facing towards B

    // Get angle we'd need to look straight at B
    float angle = (float)(-atan2( (double)B.x - A.x , (double)B.y - A.y) * 180 / M_PI - 180);
    // Keep rotation in a nice 360 circle
    if(angle <= -1) angle = 360 + angle;
    if(angle >= 360) angle = angle - 360;
    // Now check if our rotation falls in our field of view, 60 degrees on each side
    if(rotationA < angle - 60 || rotationA > angle + 60)
        return false;

    // Now, check the line of sight
    bool steep = (fabs(B.y - A.y) > fabs(B.x - A.x));
    if(steep)
    {
        std::swap(A.x, A.y);
        std::swap(B.x, B.y);
    }

    if(A.x > B.x)
    {
        std::swap(A.x, B.x);
        std::swap(A.y, B.y);
    }

    float dx = B.x - A.x;
    float dy = fabs(B.y - A.y);

    float error = dx / 2.0f;
    int yStep = (A.y < B.y) ? 1 : -1;
    int y = (int)A.y;

    int maxX = (int)B.x;

    int x;
    for(x=(int)A.x; x < maxX; x++)
    {
        if(steep)
        {
            if(levelmap[x / TILE_WIDTH][y / TILE_HEIGHT] != 0) return false;
        }
        else
        {
            if(levelmap[y / TILE_HEIGHT][x / TILE_WIDTH] != 0) return false;
        }

        error -= dy;
        if(error < 0)
        {
            y += yStep;
            error += dx;
        }
    }

    return true;
}

1 comment(s) | Tags: coding, c++, programming, game, development, line of sight, line, of, sight