Game jump logic | 易学教程

问题

I am creating a 2D Mario game.

The following function is intended to update a player's position when a particular key is pressed. The player is allowed to move left and right, and jump in the same place, or jump to the left or to the right (to form like an arc).

 bool updatePlayerPosition(Movement* mov){
        if (this->keyPressed(SDLK_RIGHT)) {
            mov->applyForce(1); // Changes the velocity in X
        }   
        if (this->keyPressed(SDLK_LEFT)) {
            mov->applyForce(-1);  // Changes the velocity in X
        }           
        if (this->keyPressed(SDLK_SPACE)) {
            mov->jump();        // Changes the velocity in Y
        }       
        if (this->keyPressed(SDLK_DOWN)) {
            mov->fallDown();   // Changes the velocity in X and Y
        }

        Point* pos = mov->getPosition();

        // Check whether the position is out of bounds
        if(Level::allowsMove(pos)){
              // If it is not, I update the player's current position
              position->x = pos->x;
              position->y = pos->y;
              return true;
        }
        // If the movement is not allowed, I don't change the position
        else {
              mov->setPosition(*position);
              return false;
        }
    }

Here is the bug: when I hit the end of the level (which has a fixed width), and if I try to move right and jump at the same time, the player jumps and stays in the air. Only when I release the space bar does the Player come to the ground.

How can I fix this?

回答1:

For your game, I think you only want the player to jump whenever space is pressed and when the player is on the floor. You must then check if the player is on the floor to have the desired behavior.

I suggest you device a mechanism like this:

if (this->keyPressed(SDLK_SPACE) && this->isOnTheFloor()) {
                                 ^^^^^^^^^^^^^^^^^^^^^^^
   mov->jump();        // Changes the velocity in Y
}

回答2:

Your spacebar handler should only apply force one time - on key down, or up, if you prefer, not every frame. On spacebar down, velocity 'up' should be set to some (likely constant) value. Then every frame, if not on the ground, velocity down should be increase a specified amount, with a maximum speed. So OnSpacebarDown, YVelocity = 10.0; and for each frame if(!bGrounded) YVelocity -= 1.0;

来源：https://stackoverflow.com/questions/13023652/game-jump-logic

标签

c++

algorithm

sdl