Get started with animated typography/particles in javascript (mapping particles to a word)?

问题

Alright, so I have a good deal of experience with HTML and CSS, and some experience with Javascript (I can write basic functions and have coded in similar languages).

I'm looking to start some visual projects and am specifically interested in getting into particle systems. I have an idea for something similar to Codecademy's name generator here (https://www.codecademy.com/courses/animate-your-name/0/1) where particles are mapped to a word and move if hovered over. It seems as though alphabet.js is what's really behind Codecademy's demo however I can't understand exactly how they mapped the particles to a word, etc.

I've done some basic tutorials just creating rudimentary particles in a canvas but I'm not sure a canvas is the best way to go - demos that utilize one of the many libraries available (such as http://soulwire.github.io/sketch.js/examples/particles.html) don't use a canvas.

So my question is - what is the best way for a beginner/intermediate in Javascript to start with particle systems? Specifically to accomplish the Codecademy name effect or similar? Should I try to use canvas or which library would be best to start with and how would you recommend starting?

回答1:

The code for this project is achievable for your intermediate JS programmer status.

How the CodeAcademy project works ...

• Start by building each letter out of circles and saving each circle's centerpoint in an array. The alphabet.js script holds that array of circle centerpoints.

• On mousemove events, test which circles are within a specified radius of the mouse position. Then animate each of those discovered circles radially outward from the mouse position using simple trigonometry.

• When the mouse moves again, test which circles are no longer within the specified radius of the current mouse position. Then animate each of those "outside" circles back towards their original positions.

You can also use native html5 canvas without any libraries...

Another approach allowing any text to be "dissolved" and reassembled

• Start by drawing the text on the canvas. BTW, this approach will "dissolve" any drawing, not just text.

• Use context.getImageData to fetch the opacity value of every pixel on the canvas. Determine which pixels on the canvas contain parts of the text. You can tell if a pixel is part of the text because it will be opaque rather than transparent.

Now do the same procedure that CodeAcademy did with their circles -- but use your pixels:

• On mousemove events, test which pixels are within a specified radius of the mouse position. Then animate each of those discovered pixels radially outward from the mouse position using simple trigonometry.

• When the mouse moves again, test which pixels are no longer within the specified radius of the current mouse position. Then animate each of those "outside" pixels back towards their original positions.

[Addition: mousemove event to test if circles are within mouse distance]

Note: You probably want to keep an animation frame running that moves circles closer or further from their original positions based on a flag (isInside) for each circle.

function handleMouseMove(e){
    // tell the browser we're handling this event
    e.preventDefault();
    e.stopPropagation();
    // calc the current mouse position
    mouseX=parseInt(e.clientX-offsetX);
    mouseY=parseInt(e.clientY-offsetY);

    // test each circle to see if it's inside or outside
    // radius of 40px to current mouse position
    // circles[] is an array of circle objects shaped like this
    //      {x:,y:,r:,originalX:,originalY:,isInside:}
    var radius=40;
    for(var i=0;i<circles.length;i++){
        var c=circles[i];
        var dx=c.x-mouseX;
        var dy=c.y-mouseY;
        if(dx*dx+dy*dy<radius*radius){
            c.isInside=true;
            // move c.x & c.y away from its originalX & originalY
        }else{
            c.isInside=false;
            // if the circle is not already back at it's originalX, originalY
            // then move c.x & c.y back towards its originalX, originalY
        }
    }
}

来源：https://stackoverflow.com/questions/36369819/get-started-with-animated-typography-particles-in-javascript-mapping-particles