S2JS - Rotating, flipping, pointing - another game : Fixing the jitters

The solution, in English, is "if the distance to go is less than how far we'd move in a single frame, then don't bother moving".

In code, we compare the distance to the velocity, and set the velocity to zero.

The only wrinkle is that we're dealing with both positive and negative values, and what we mean by "less than" is actually "nearer to zero". So we take the absolute (always positive) value of each before we do the comparison:

if (Math.abs(distance_x) < Math.abs(this.velocity_x)) this.velocity_x = 0; if (Math.abs(distance_y) < Math.abs(this.velocity_y)) this.velocity_y = 0;

Jitters fixed !

<html> <body> <canvas id="myCanvas" width=300 height=300 style="background-color:MediumSeaGreen"> </canvas> <script> var ctx = myCanvas.getContext("2d"); // Get the drawing context for the canvas var FPS = 40; // How many frames per second var mouse_x = 0; var mouse_y = 0; // Where is the mouse function MySprite (img_url) { this.x = 0; this.y = 0; this.visible= true; this.velocity_x = 0; this.velocity_y = 0; this.MyImg = new Image(); this.MyImg.src = img_url ; this.angle = 0; // How many degrees we are rotated this.flipV = false; // Are we flipped vertically this.flipH = false; // Are we flipped horizontally } MySprite.prototype.Do_Frame_Things = function() { ctx.save(); ctx.translate(this.x + this.MyImg.width/2, this.y + this.MyImg.height/2); ctx.rotate(this.angle * Math.PI / 180); if (this.flipV) ctx.scale(1,-1); if (this.flipH) ctx.scale(-1,1); if (this.visible) ctx.drawImage(this.MyImg, -this.MyImg.width/2, -this.MyImg.height/2); ctx.restore(); this.x = this.x + this.velocity_x; this.y = this.y + this.velocity_y; // move the thing } function MyTouchMoveHandler(MyEvent) { var rect = myCanvas.getBoundingClientRect(); mouse_x = MyEvent.touches[0].clientX - rect.left; mouse_y = MyEvent.touches[0].clientY - rect.top; MyEvent.preventDefault() } addEventListener("touchmove", MyTouchMoveHandler); addEventListener("touchstart", MyTouchMoveHandler); function MyMouseMoveHandler (MyEvent) { var rect = myCanvas.getBoundingClientRect(); mouse_x= MyEvent.clientX - rect.left; mouse_y= MyEvent.clientY - rect.top; } addEventListener("mousemove", MyMouseMoveHandler); MySprite.prototype.Point_Towards = function(target_x, target_y) { var distance_x = target_x - (this.x + this.MyImg.width/2); var distance_y = target_y - (this.y + this.MyImg.height/2); this.angle = (Math.atan2(distance_y, distance_x) * 180 / Math.PI) + 90; } MySprite.prototype.Move_Towards = function(target_x, target_y, speed) { var distance_x = target_x - (this.x + this.MyImg.width / 2); var distance_y = target_y - (this.y + this.MyImg.height / 2); var actual_distance = Math.sqrt(distance_x * distance_x + distance_y * distance_y); // Thanks, Pythagoras! this.velocity_x = distance_x / actual_distance * speed ; this.velocity_y = distance_y / actual_distance * speed ; if (Math.abs(distance_x) < Math.abs(this.velocity_x)) this.velocity_x = 0; if (Math.abs(distance_y) < Math.abs(this.velocity_y)) this.velocity_y = 0; } function Do_a_Frame () { ctx.clearRect(0, 0, myCanvas.width, myCanvas.height); // clear the frame jelly.Point_Towards(mouse_x, mouse_y); // tell jelly to point to mouse jelly.Move_Towards(mouse_x, mouse_y, 3); // and move that way jelly.Do_Frame_Things(); // let the jelly do its thing } var jelly= new MySprite("http://s2js.com/img/etc/jellyfish2.png"); jelly.x=120; jelly.y=120; setInterval(Do_a_Frame, 1000/FPS); // set my frame renderer </script> </body> </html>