Question

I keep looking up on the internet how to move from point A to point B on an angle with a specified distance. When I tried to code it, however, the camera just gets messed up and I’m moving in random directions. I am using SDL/OpenGL with c++ and this is my player function. Right now, I’m trying to get the player to move forwards along the angle.

void player_action()
{

    if (SDL_PollEvent(&event))
    {
        switch (event.type)
        {
            case SDL_MOUSEMOTION:
                {
                    player.rotxl = (screen->w)/2;
                    player.rotxd = event.motion.x - player.rotxl;
                    player.rotx = player.rotx + (player.rotxd/4);
                    if (player.rotx < 0)
                    {
                        player.rotx = player.rotx + 360;
                    };
                    if (player.rotx > 360)
                    {
                        player.rotx = player.rotx - 360;
                    }
                };
            break;

            case SDL_KEYDOWN:
                switch (event.key.keysym.sym)
                {
                    case SDLK_w:
                        {player.zvel = 8.0f;}; break;
                    case SDLK_a:
                        {player.xvel = 8.0f;}; break;
                    case SDLK_s:
                        {player.zvel = -8.0f;}; break;
                    case SDLK_d:
                        {player.xvel = -8.0f;}; break;
                    case SDLK_ESCAPE:
                        {running = false;}; break;
                    default: break;

                }; break;

            case SDL_KEYUP:
                switch(event.key.keysym.sym)
                {
                    case SDLK_w:
                        {player.zvel = 0.0f;}; break;
                    case SDLK_a:
                        {player.xvel = 0.0f;}; break;
                    case SDLK_s:
                        {player.zvel = 0.0f;}; break;
                    case SDLK_d:
                        {player.xvel = 0.0f;}; break;
                    default: break;
                };
            break;
        };

    };

    player.x = player.x + float(player.zvel*cos((double)player.rotx));
    player.z = player.z + float(player.zvel*sin((double)player.rotx));

    glRotatef(player.rotx, 0.0f, 1.0f, 0.0f);
    glTranslatef(player.x, player.y, player.z);

    SDL_WarpMouse((screen->w/2), (screen->h/2));
};

Answer 1

If I’m correct the math functions sin and cos both take angles in radians, not degrees as player.rotx seems to be. Try the following:

player.x = player.x + float(player.zvel*cos((double)player.rotx*0.0174532925));
player.z = player.z + float(player.zvel*sin((double)player.rotx*0.0174532925));

We’re multiplying player.rotx by pi/180, which is how we convert degrees to radians.

Not sure if this is your only problem, but it certainly appears to be one of them.