What do I need to do to this animation to make the text animate along with the background image?
I have seen a couple of different examples online but either they don't have the text rotated like I do (which is causing the problem) or they don't explain the maths behind the solution.
This is quite good - http://tech.pro/tutorial/1008/creating-a-roulette-wheel-using-html5-canvas but it doesn't offer a great insight into the use of any of the Math functions.
I obviously need to affect the line:
context.rotate(i * arc);
in the loop that writes the text but I am unsure of the maths involved.
var cvs = document.getElementById("cvs");
var context = cvs.getContext("2d");
var height = 400,
width = 400,
spinning = false,
angle = 0,
awards = [100,200,300,400,500,600,700,800,900,1000,1100,1200],
segmentCount = 12,
angleAmount = 30,
arc = Math.PI / 6,
image = new Image();
image.src = 'http://placehold.it/400x400';
function draw() {
// clear
context.clearRect(0,0,width,height);
// rotate whole wheel here?
context.save();
context.translate(height/2, width/2);
context.rotate(angle * (Math.PI / 180));
context.drawImage(image,-width/2,-height/2);
context.restore();
// draw the prize amount text
for(var i = 0; i < segmentCount; i++){
context.save();
context.translate(height/2, width/2);
context.font = "bold 18px sans-serif";
context.textAlign = "end";
context.rotate(i * arc);
context.fillStyle = "#000000";
context.textBaseline = 'middle';
context.fillText(awards[i],145,0);
context.restore();
angle += angleAmount;
}
}
function update(){
draw();
angle += 5;
setTimeout(update,1000/30);
}
image.onload = update;
I think you got confused by the way you are using the 'angle' var : it is in fact the var that holds the current rotation, and you also use it in the for loop that draws the amounts (angle+=angleAmount)... just to increase it. Luckily enough you add 360° to it so it did not create a bug.
So first thing is to stop increasing this var in the text drawing for loop, second thing is to add the current rotation angle to each text draw (with a degree-> rad conversion) :
context.rotate(( i * angleAmount + angle ) * (Math.PI / 180));
http://jsfiddle.net/gamealchemist/fwter56k/4/
(or with a bit of optimisation : http://jsfiddle.net/gamealchemist/fwter56k/5/ )
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