What is the best way to implement gravity in order to make my character jump effectively

Question

What is the best way to implement gravity in order to make my character jump effectively

As a beginner in the world of coding, I am currently working on creating a game. However, one major challenge I am facing is simulating gravity to make my character jump effectively. Despite trying various methods, I have encountered disappointing results. Below is a snippet of my code:

#canvas {
  border: 1px solid #d3d3d3;
  background-color: #f1f1f1;
}

<body>

  <canvas id='canvas' width='512px' height='300px'></canvas>

  <script>
    let canvas = document.getElementById('canvas');
    let ctx = canvas.getContext('2d');
    let charX = 20;
    let charY = 130;
    let charSide = 20;
    let velocity = 0;
    let resistance = 0;
    let rightPressed = false;
    let leftPressed = false;
    let upPressed = false;
    let aPressed = false;
    let dPressed = false;

    function drawRect(x, y, width, height, color) {
      ctx.beginPath();
      ctx.rect(x, y, width, height);
      ctx.fillStyle = color;
      ctx.fill();
      ctx.closePath();
    }

    function drawGround(x, y, count) {
      if (count === undefined) {
        count = 1;
      }
      drawRect(x, y, 32 * count, canvas.height - y, '#684027');
      drawRect(x, y, 32 * count, 10, 'green');
    }

    function draw() {
      //Updates Game
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      //Draws Character
      drawRect(charX, charY, charSide, charSide, 'lime');
      //Draws Ground
      drawGround(0, 150, 16);
      //Moves Character
      if (charY = 130) {
        speed = 0;
        accelerate = 0;
      }
      if (rightPressed && charX < canvas.width - charSide) {
        charX += 2;
      } else if (leftPressed && charX > 0) {
        charX -= 2;
      } else if (upPressed && charY > 0 && charY < 131) {
        velocity = 0;
        velocity += 50;
        resistance++;
        velocity -= resistance;
        charY -= velocity;
      } else if (upPressed === false && charY > 129) {
        resistance = 0;
        velocity = 0;
      }
    }
    //Character Movement Logic
    document.addEventListener("keydown", keyDownHandler, false);
    document.addEventListener("keyup", keyUpHandler, false);

    function keyDownHandler(e) {
      if (e.keyCode == 39) {
        rightPressed = true;
      } else if (e.keyCode == 37) {
        leftPressed = true;
      } else if (e.keyCode == 38) {
        upPressed = true;
      } else if (e.keyCode == 65) {
        aPressed = true;
      } else if (e.keyCode == 68) {
        dPressed = true;
      }
    }

    function keyUpHandler(e) {
      if (e.keyCode == 39) {
        rightPressed = false;
      } else if (e.keyCode == 37) {
        leftPressed = false;
      } else if (e.keyCode == 38) {
        upPressed = false;
      } else if (e.keyCode == 65) {
        aPressed = false;
      } else if (e.keyCode == 68) {
        dPressed = false;
      }
    }
    //Animates Game
    setInterval(draw, 10);
  </script>

</body>

In an attempt to implement gravity for character jumping, I experimented with variables like velocity and resistance but unfortunately, it did not yield the desired outcome.

javascript css html5-canvas

Answer 1

Answer №1

Elementary game physics

When it comes to animating, the key is to use requestAnimationFrame to control the timing of the animation. The example below illustrates how this can be achieved.

Gravity

The most basic form of gravity involves assuming a consistent frame rate. An object possesses both a y position and a y speed (delta y). Gravity acts as a constant force that incrementally increases the delta y each frame.

obj = {
   y : 0,  // position
   dy : 0, // speed
   size : 20, // height
   onGround : false,  // true if on the ground
   drag : 0.99, // with drag being 0.01 
}
const grav = 0.1;

On each frame (animation tick), apply gravity and update the position accordingly.

obj.dy += grav;
obj.y += obj.dy;

If the object reaches the ground, reset its delta y to zero.

if(obj.y + obj.size >= 150){ // collision with ground
   obj.y = 150 - obj.size;  // reposition on the ground
   obj.dy = 0;              // stop delta y
   obj.onGround = true;
}else{
   obj.onGround = false;
}

Subsequently, proceed to draw the character.

Jump

To execute a jump for the character, set the delta y to a negative value only when the character is grounded. The code above ensures that the character descends back down in due course.

if(keyboard.up && obj.onGround){
   obj.dy = -5;
}

Drag

To introduce resistance or drag proportional to the speed, incorporate a drag coefficient. Multiply the delta y by this coefficient after adding the gravitational force every frame.

obj.dy *= obj.drag;  // decrease speed due to drag

The example segment portrays a player capable of jumping off the ground and moving horizontally. There exists some drag during the jump, while significant drag applies when the player is stationed on the ground for horizontal movement.

Demonstration

const ctx = canvas.getContext('2d');

// Simple keyboard event handler
const keyboard = (() => {
  document.addEventListener("keydown", keyHandler);
  document.addEventListener("keyup", keyHandler);
  const keyboard = {
    right: false,
    left: false,
    up: false,
    any : false,
  };
  function keyHandler(e) {
    const state = e.type === "keydown"
    if (e.keyCode == 39) {
      keyboard.right = state;
    } else if (e.keyCode == 37) {
      keyboard.left = state;
    } else if (e.keyCode == 38) {
      keyboard.up = state;
      e.preventDefault();
    }
    if(state) { keyboard.any = true } // must reset when used
  }
  return keyboard;
})();

// define the player.
// update() updates position and responds to keyboard input
// draw() displays the player
// start() establishes initial position and state
const player = {
  x: 0,
  y: 0,
  dx: 0, // delta x and y
  dy: 0,
  size: 20,
  color: 'lime',
  onGround: false,
  jumpPower: -5,  // intensity of jump (smaller value implies higher jumps eg. -10 smaller than -5)
  moveSpeed: 2,
  update() {
    // react based on keyboard state
    if (keyboard.up && this.onGround) { this.dy = this.jumpPower }
    if (keyboard.left) { this.dx = -this.moveSpeed }
    if (keyboard.right) { this.dx = this.moveSpeed }
 
    // apply gravity, drag, and move the player
    this.dy += world.gravity;
    this.dy *= world.drag;
    this.dx *= this.onGround ? world.groundDrag : world.drag;
    this.x += this.dx;
    this.y += this.dy;

    // check for ground contact and boundary limits
    if (this.y + this.size >= world.ground) {
      this.y = world.ground - this.size;
      this.dy = 0;
      this.onGround = true;
    } else {
      this.onGround = false;
    }
    if (this.x > ctx.canvas.width) {
      this.x -= ctx.canvas.width;
    } else if (this.x + this.size < 0) {
      this.x += ctx.canvas.width;
    }
  },
  draw() {
    drawRect(this.x, this.y, this.size, this.size, this.color);
  },
  start() {
    this.x = ctx.canvas.width / 2 - this.size / 2;
    this.y = world.ground - this.size;
    this.onGround = true;
    this.dx = 0;
    this.dy = 0;
  }
}
// define world
const world = {
  gravity: 0.2, // gravity strength per frame
  drag: 0.999, // adjust to modify drag
  groundDrag: 0.9, // tweak to alter ground movement
  ground: 150,
}
// establish starting point
player.start();
// initiate first frame logic after running all other code
requestAnimationFrame(mainLoop); // commence upon readiness

// From OP
function drawRect(x, y, width, height, color) {
  ctx.beginPath();
  ctx.rect(x, y, width, height);
  ctx.fillStyle = color;
  ctx.fill();
  ctx.closePath();
}

function drawGround(x, y, count = 1) {
  drawRect(x, y, 32 * count, canvas.height - y, '#684027');
  drawRect(x, y, 32 * count, 10, 'green');
}
// indication display
var showI = true;
// main animation loop
function mainLoop(time) { // time supplied by requestAnimationFrame        
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  drawGround(0, world.ground, 16);
  player.update();
  player.draw();
  if(showI){
     if(keyboard.any){
         keyboard.any = false;
         showI = false;
     }
     ctx.textAlign = "center";
     ctx.font = "24px arial";
     ctx.fillStyle = "#000";
     ctx.fillText("Up arrow to jump. Left right to move",ctx.canvas.width / 2, 80);
  }
  requestAnimationFrame(mainLoop);
}

// ensure window focus for keyboard inputs
window.focus();

#canvas {
  border: 1px solid #d3d3d3;
  background-color: #f1f1f1;
}

<canvas id='canvas' width='512px' height='300px'></canvas>

Answer 2

Elementary game physics

When it comes to animating, the key is to use requestAnimationFrame to control the timing of the animation. The example below illustrates how this can be achieved.

Gravity

The most basic form of gravity involves assuming a consistent frame rate. An object possesses both a y position and a y speed (delta y). Gravity acts as a constant force that incrementally increases the delta y each frame.

obj = {
   y : 0,  // position
   dy : 0, // speed
   size : 20, // height
   onGround : false,  // true if on the ground
   drag : 0.99, // with drag being 0.01 
}
const grav = 0.1;

On each frame (animation tick), apply gravity and update the position accordingly.

obj.dy += grav;
obj.y += obj.dy;

If the object reaches the ground, reset its delta y to zero.

if(obj.y + obj.size >= 150){ // collision with ground
   obj.y = 150 - obj.size;  // reposition on the ground
   obj.dy = 0;              // stop delta y
   obj.onGround = true;
}else{
   obj.onGround = false;
}

Subsequently, proceed to draw the character.

Jump

To execute a jump for the character, set the delta y to a negative value only when the character is grounded. The code above ensures that the character descends back down in due course.

if(keyboard.up && obj.onGround){
   obj.dy = -5;
}

Drag

To introduce resistance or drag proportional to the speed, incorporate a drag coefficient. Multiply the delta y by this coefficient after adding the gravitational force every frame.

obj.dy *= obj.drag;  // decrease speed due to drag

The example segment portrays a player capable of jumping off the ground and moving horizontally. There exists some drag during the jump, while significant drag applies when the player is stationed on the ground for horizontal movement.

Demonstration

const ctx = canvas.getContext('2d');

// Simple keyboard event handler
const keyboard = (() => {
  document.addEventListener("keydown", keyHandler);
  document.addEventListener("keyup", keyHandler);
  const keyboard = {
    right: false,
    left: false,
    up: false,
    any : false,
  };
  function keyHandler(e) {
    const state = e.type === "keydown"
    if (e.keyCode == 39) {
      keyboard.right = state;
    } else if (e.keyCode == 37) {
      keyboard.left = state;
    } else if (e.keyCode == 38) {
      keyboard.up = state;
      e.preventDefault();
    }
    if(state) { keyboard.any = true } // must reset when used
  }
  return keyboard;
})();

// define the player.
// update() updates position and responds to keyboard input
// draw() displays the player
// start() establishes initial position and state
const player = {
  x: 0,
  y: 0,
  dx: 0, // delta x and y
  dy: 0,
  size: 20,
  color: 'lime',
  onGround: false,
  jumpPower: -5,  // intensity of jump (smaller value implies higher jumps eg. -10 smaller than -5)
  moveSpeed: 2,
  update() {
    // react based on keyboard state
    if (keyboard.up && this.onGround) { this.dy = this.jumpPower }
    if (keyboard.left) { this.dx = -this.moveSpeed }
    if (keyboard.right) { this.dx = this.moveSpeed }
 
    // apply gravity, drag, and move the player
    this.dy += world.gravity;
    this.dy *= world.drag;
    this.dx *= this.onGround ? world.groundDrag : world.drag;
    this.x += this.dx;
    this.y += this.dy;

    // check for ground contact and boundary limits
    if (this.y + this.size >= world.ground) {
      this.y = world.ground - this.size;
      this.dy = 0;
      this.onGround = true;
    } else {
      this.onGround = false;
    }
    if (this.x > ctx.canvas.width) {
      this.x -= ctx.canvas.width;
    } else if (this.x + this.size < 0) {
      this.x += ctx.canvas.width;
    }
  },
  draw() {
    drawRect(this.x, this.y, this.size, this.size, this.color);
  },
  start() {
    this.x = ctx.canvas.width / 2 - this.size / 2;
    this.y = world.ground - this.size;
    this.onGround = true;
    this.dx = 0;
    this.dy = 0;
  }
}
// define world
const world = {
  gravity: 0.2, // gravity strength per frame
  drag: 0.999, // adjust to modify drag
  groundDrag: 0.9, // tweak to alter ground movement
  ground: 150,
}
// establish starting point
player.start();
// initiate first frame logic after running all other code
requestAnimationFrame(mainLoop); // commence upon readiness

// From OP
function drawRect(x, y, width, height, color) {
  ctx.beginPath();
  ctx.rect(x, y, width, height);
  ctx.fillStyle = color;
  ctx.fill();
  ctx.closePath();
}

function drawGround(x, y, count = 1) {
  drawRect(x, y, 32 * count, canvas.height - y, '#684027');
  drawRect(x, y, 32 * count, 10, 'green');
}
// indication display
var showI = true;
// main animation loop
function mainLoop(time) { // time supplied by requestAnimationFrame        
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  drawGround(0, world.ground, 16);
  player.update();
  player.draw();
  if(showI){
     if(keyboard.any){
         keyboard.any = false;
         showI = false;
     }
     ctx.textAlign = "center";
     ctx.font = "24px arial";
     ctx.fillStyle = "#000";
     ctx.fillText("Up arrow to jump. Left right to move",ctx.canvas.width / 2, 80);
  }
  requestAnimationFrame(mainLoop);
}

// ensure window focus for keyboard inputs
window.focus();

#canvas {
  border: 1px solid #d3d3d3;
  background-color: #f1f1f1;
}

<canvas id='canvas' width='512px' height='300px'></canvas>

Answer 3

Answer №2

Here are a few suggestions to improve your project:

One key issue lies in the velocities and resistances of your objects. Try adjusting these factors for better results.
Consider running your animations based on time instead of updating positions with every draw call. This will ensure consistency regardless of rendering rate.
Create an encapsulated object model that includes properties affected by gravity. This organizational strategy can help maintain sanity during code development.
Explore tutorials available online for helpful techniques and tips on addressing these challenges.

Answer 4

Here are a few suggestions to improve your project:

One key issue lies in the velocities and resistances of your objects. Try adjusting these factors for better results.
Consider running your animations based on time instead of updating positions with every draw call. This will ensure consistency regardless of rendering rate.
Create an encapsulated object model that includes properties affected by gravity. This organizational strategy can help maintain sanity during code development.
Explore tutorials available online for helpful techniques and tips on addressing these challenges.

What is the best way to implement gravity in order to make my character jump effectively

Answer №1

Elementary game physics

Gravity

Jump

Drag

Demonstration

Answer №2

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