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Pinch/pucker an image in canvas

由 女生的网名这么多〃 提交于 2021-02-16 13:39:25

问题


How can I pinch/pucker some area of an image in canvas?

I've made a solar system animation some time ago, and I started rewriting it. Now, I want to add gravity effect to masses. To make the effect visible, I turned the background into a grid and I'll be modifying it.

Desired effect is something like this (made in PS)

context.background("rgb(120,130,145)");
context.grid(25, "rgba(255,255,255,.1)");

var sun = {
    fill        : "rgb(220,210,120)",
    radius      : 30,
    boundingBox : 30*2 + 3*2,
    position    : {
        x       : 200,
        y       : 200,
    },
};
sun.img = saveToImage(sun);

context.drawImage(sun.img, sun.position.x - sun.boundingBox/2, sun.position.y - sun.boundingBox/2);

jsFiddle

Update: I've done some googling and found some resources, but since I've never done pixel manipulation before, I can't put these together.

Pixel Distortions with Bilinear Filtration in HTML5 Canvas | Splashnology.com (functions only)

glfx.js (WebGL library with demos)

jsFiddle (spherize, zoom, twirl examples)

The spherize effect in inverted form would be good for the job, I guess.


回答1:


UPDATED answer I have improved the performance significantly but reduced the flexibility.

To get a pinch effect you need to use a mask and then redraw the image with the mask. In this case you use a circular mask that you shrink as you draw zoomed in or out copies of the original. The effect is a buldge or pinch.

There is a quality setting that will give you from sub pixel rendering up to very rough. As with these things you sacrifice speed for quality.

I would not recommend this as a final solution to your requirements because of the inconsistent rendering speed between hardware and browsers.

For consistent results you need to use webGL. If I get time I will write a shader to do that if there is not already on on ShaderToy

So this is a pure canvas 2d solution. Canvas 2d can do anything, it just cant do it as quickly as webGL but it can come close.

UPDATE: Have re written example to improve the speed. Now runs a lot faster using clip rather than a pixel mask. Though new version is limited to pinch bulge on both axis at the same time.

See code comments for more info. I have tried to explain it best I can, if you have question do ask. I wish I could have given you a perfect answer but canvas 2d API needs to grow up some more before things like this can be more reliable.

var canvas = document.getElementById("canV");
var ctx = canvas.getContext("2d");



var createImage= function(w,h){ // create a image of requier size
    var image = document.createElement("canvas"); 
    image.width = w;
    image.height =h;
    image.ctx = image.getContext("2d");  // tack the context onto the image
    return image;
}

// amountX amountY the amount of the effect
// centerX,centerY the center of the effect
// quality the quality of the effect. The smaller the vall the higher the quallity but the slower the processing
// image, the input image
// mask an image to hold the mask. Can be a different size but that will effect quality
// result, the image onto which the effect is rendered
var pinchBuldge = function(amountX,quality,image,result){
    var w = image.width;
    var h = image.height;
    var easeW = (amountX/w)*4; // down unit 0 to 4 top to bottom
    var wh = w/2;   // half size for lazy coder
    var hh = h/2;            
    var stepUnit = (0.5/(wh))*quality;
    result.ctx.drawImage(image,0,0);
    for(i = 0; i < 0.5; i += stepUnit){  // all done in normalised size                                             
        var r = i*2;  // normalise i
        var x = r*wh;  // get the clip x destination pos relative to center
        var y = r*hh;  // get the clip x  destination pos relative to center
        var xw = w-(x*2);  // get the clip  destination width
        var rx = (x)*easeW;   // get the image source pos
        var ry = (y)*easeW;
        var rw = w-(rx*2);     // get the image source size
        var rh = h-(ry*2);
        result.ctx.save();
        result.ctx.beginPath();
        result.ctx.arc(wh,hh,xw/2,0,Math.PI*2);
        result.ctx.clip();
        result.ctx.drawImage(image,rx,ry,rw,rh,0,0,w,h);
        result.ctx.restore();
    }        
    // all done;

}
// create the requiered images
var imageSize = 256; // size of image
var image = createImage(imageSize,imageSize);  // the original image
var result = createImage(imageSize,imageSize); // the result image
image.ctx.fillStyle = "#888";  // add some stuff to the image
image.ctx.fillRect(0,0,imageSize,imageSize);  // fil the background
// draw a grid  Dont need to comment this I hope it is self evident
var gridCount = 16;
var grid = imageSize/gridCount;
var styles = [["black",8],["white",2]];
styles.forEach(function(st){
    image.ctx.strokeStyle = st[0];
    image.ctx.lineWidth = st[1];
    for(var i = 0; i < 16; i++){
        image.ctx.moveTo(i*grid,0);
        image.ctx.lineTo(i*grid,imageSize)
        image.ctx.moveTo(0,i*grid);
        image.ctx.lineTo(imageSize,i*grid)
    }
    image.ctx.moveTo(0,imageSize-1);  
    image.ctx.lineTo(imageSize,imageSize-1)
    image.ctx.moveTo(imageSize-1,0);
    image.ctx.lineTo(imageSize-1,imageSize)
    image.ctx.stroke()
});


var timer = 0;
var rate = 0.05
// Quality 0.5 is sub pixel high quality
//         1 is pixel quality
//         2 is every 2 pixels
var quality = 1.5; // quality at OK

function update(){
    timer += rate;
    var effectX = Math.sin(timer)*(imageSize/4);
    pinchBuldge(effectX,quality,image,result);
    ctx.drawImage(result,0,0);
    setTimeout(update,10); // do the next one in 100 milliseconds
}
update();
.canC {
    width:256px;
    height:256px;
}
<canvas class="canC" id="canV" width=256 height=256></canvas>



回答2:


I've had time to revisit this problem and came up with a solution. Instead of solving the problem directly, first, I needed to understand how the math behind the calculation and pixel manipulation works.

So, instead of using an image/pixels, I decided to use particles. A JavaScript object is something I'm much more familiar with, so it was easy to manipulate.

I'll not try to explain the method because I think it's self-explanatory, and I tried to keep it as simple as it can get.

var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");

canvas.width  = 400;
canvas.height = 400;

var particles = [];

function Particle() {
    this.position = {
        actual : {
            x : 0,
            y : 0
        },
        affected : {
            x : 0,
            y : 0
        },
    };
}

// space between particles
var gridSize = 25;

var columns  = canvas.width / gridSize;
var rows     = canvas.height / gridSize;

// create grid using particles
for (var i = 0; i < rows+1; i++) {
    for (var j = 0; j < canvas.width; j += 2) {
        var p = new Particle();
        p.position.actual.x = j;
        p.position.actual.y = i * gridSize;
        p.position.affected = Object.create(p.position.actual);
        particles.push(p);
    }
}
for (var i = 0; i < columns+1; i++) {
    for (var j = 0; j < canvas.height; j += 2) {
        var p = new Particle();
        p.position.actual.x = i * gridSize;
        p.position.actual.y = j;
        p.position.affected = Object.create(p.position.actual);
        particles.push(p);
    }
}

// track mouse coordinates as it is the source of mass/gravity
var mouse = {
    x : -100,
    y : -100,
};

var effectRadius = 75;
var effectStrength = 50;

function draw() {
    context.clearRect(0, 0, canvas.width, canvas.height);
    
    particles.forEach(function (particle) {
        // move the particle to its original position
        particle.position.affected = Object.create(particle.position.actual);
        
        // calculate the effect area
        var a = mouse.y - particle.position.actual.y;
        var b = mouse.x - particle.position.actual.x;
        var dist = Math.sqrt(a*a + b*b);
        
        // check if the particle is in the affected area
        if (dist < effectRadius) {
            
            // angle of the mouse relative to the particle
            var a = angle(particle.position.actual.x, particle.position.actual.y, mouse.x, mouse.y);
            
            // pull is stronger on the closest particle
            var strength = dist.map(0, effectRadius, effectStrength, 0);
            
            if (strength > dist) {
                strength = dist;
            }
            
            // new position for the particle that's affected by gravity
            var p = pos(particle.position.actual.x, particle.position.actual.y, a, strength);
            
            particle.position.affected.x = p.x;
            particle.position.affected.y = p.y;
        }
        
        context.beginPath();
        context.rect(particle.position.affected.x -1, particle.position.affected.y -1, 2, 2);
        context.fill();
    });
}

draw();

window.addEventListener("mousemove", function (e) {
    mouse.x = e.x - canvas.offsetLeft;
    mouse.y = e.y - canvas.offsetTop;
    requestAnimationFrame(draw);
});

function angle(originX, originY, targetX, targetY) {
    var dx = targetX - originX;
    var dy = targetY - originY;
    var theta = Math.atan2(dy, dx) * (180 / Math.PI);
    if (theta < 0) theta = 360 + theta;
    return theta;
}

Number.prototype.map = function (in_min, in_max, out_min, out_max) {
    return (this - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
};

function pos(x, y, angle, length) {
    angle *= Math.PI / 180;
    return {
        x : Math.round(x + length * Math.cos(angle)),
        y : Math.round(y + length * Math.sin(angle)),
    };
}
* {
  margin: 0;
  padding: 0;
  box-sizing: inherit;
  line-height: inherit;
  font-size: inherit;
  font-family: inherit;
}

body {
  font-family: sans-serif;
  box-sizing: border-box;
  background-color: hsl(0, 0%, 90%);
}

canvas {
  display: block;
  background: white;
  box-shadow: 0 0 2px rgba(0, 0, 0, .2), 0 1px 1px rgba(0, 0, 0, .1);
  margin: 20px auto;
}

canvas:hover {
  cursor: none;
}
<canvas id="canvas"></canvas>

I might try to create twirl effect some other time, and move these into WebGL for better performance.

Update:

Now, I'm working on the twirl effect, and I've made it work to some degree.

var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");

canvas.width  = 400;
canvas.height = 400;

var particles = [];

function Particle() {
    this.position = {
        actual : {
            x : 0,
            y : 0
        },
        affected : {
            x : 0,
            y : 0
        },
    };
}

// space between particles
var gridSize = 25;

var columns  = canvas.width / gridSize;
var rows     = canvas.height / gridSize;

// create grid using particles
for (var i = 0; i < rows+1; i++) {
    for (var j = 0; j < canvas.width; j += 2) {
        var p = new Particle();
        p.position.actual.x = j;
        p.position.actual.y = i * gridSize;
        p.position.affected = Object.create(p.position.actual);
        particles.push(p);
    }
}
for (var i = 0; i < columns+1; i++) {
    for (var j = 0; j < canvas.height; j += 2) {
        var p = new Particle();
        p.position.actual.x = i * gridSize;
        p.position.actual.y = j;
        p.position.affected = Object.create(p.position.actual);
        particles.push(p);
    }
}

// track mouse coordinates as it is the source of mass/gravity
var mouse = {
    x : -100,
    y : -100,
};

var effectRadius = 75;
var twirlAngle   = 90;

function draw(e) {
    context.clearRect(0, 0, canvas.width, canvas.height);
    
    particles.forEach(function (particle) {
        // move the particle to its original position
        particle.position.affected = Object.create(particle.position.actual);
        
        // calculate the effect area
        var a = mouse.y - particle.position.actual.y;
        var b = mouse.x - particle.position.actual.x;
        var dist = Math.sqrt(a*a + b*b);
        
        // check if the particle is in the affected area
        if (dist < effectRadius) {
            
            // angle of the particle relative to the mouse
            var a = angle(mouse.x, mouse.y, particle.position.actual.x, particle.position.actual.y);
            
            var strength = dist.map(0, effectRadius, twirlAngle, 0);
            
            // twirl
            a += strength;
            
            // new position for the particle that's affected by gravity
            var p = rotate(a, dist, mouse.x, mouse.y);
            
            particle.position.affected.x = p.x;
            particle.position.affected.y = p.y;
        }
        
        context.beginPath();
        context.rect(particle.position.affected.x -1, particle.position.affected.y -1, 2, 2);
        context.fillStyle = "black";
        context.fill();
    });
}

draw();

window.addEventListener("mousemove", function (e) {
    mouse.x = e.x - canvas.offsetLeft;
    mouse.y = e.y - canvas.offsetTop;
    requestAnimationFrame(draw);
});

function angle(originX, originY, targetX, targetY) {
    var dx = targetX - originX;
    var dy = targetY - originY;
    var theta = Math.atan2(dy, dx) * (180 / Math.PI);
    if (theta < 0) theta = 360 + theta;
    return theta;
}

Number.prototype.map = function (in_min, in_max, out_min, out_max) {
    return (this - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
};

function pos(x, y, angle, length) {
    angle *= Math.PI / 180;
    return {
        x : Math.round(x + length * Math.cos(angle)),
        y : Math.round(y + length * Math.sin(angle)),
    };
}

function rotate(angle, distance, originX, originY) {
    return {
        x : originX + Math.cos(angle * Math.PI/180) * distance,
        y : originY + Math.sin(angle * Math.PI/180) * distance,
    }
}
* {
  margin: 0;
  padding: 0;
  box-sizing: inherit;
  line-height: inherit;
  font-size: inherit;
  font-family: inherit;
}

body {
  font-family: sans-serif;
  box-sizing: border-box;
  background-color: hsl(0, 0%, 90%);
}

canvas {
  display: block;
  background: white;
  box-shadow: 0 0 2px rgba(0, 0, 0, .2), 0 1px 1px rgba(0, 0, 0, .1);
  margin: 20px auto;
}
<canvas id="canvas"></canvas>

There is a slight issue with the mapping of strength of the twirl. I've used the same function map that I've used with pinch effect, but I think twirl doesn't use linear mapping, but eased mapping. Compare the JS version with the PS filter. PS filter is smoother. I need to rewrite the map function.

Update 2:

I've managed to make it work the same way PS filter does. Using an ease function, i.e., easeOutQuad solved the problem. Enjoy :)

var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");

canvas.width  = 400;
canvas.height = 400;

var particles = [];

function Particle() {
    this.position = {
        actual : {
            x : 0,
            y : 0
        },
        affected : {
            x : 0,
            y : 0
        },
    };
}

// space between particles
var gridSize = 25;

var columns  = canvas.width / gridSize;
var rows     = canvas.height / gridSize;

// create grid using particles
for (var i = 0; i < rows+1; i++) {
    for (var j = 0; j < canvas.width; j+=2) {
        var p = new Particle();
        p.position.actual.x = j;
        p.position.actual.y = i * gridSize;
        p.position.affected = Object.create(p.position.actual);
        particles.push(p);
    }
}
for (var i = 0; i < columns+1; i++) {
    for (var j = 0; j < canvas.height; j+=2) {
        var p = new Particle();
        p.position.actual.x = i * gridSize;
        p.position.actual.y = j;
        p.position.affected = Object.create(p.position.actual);
        particles.push(p);
    }
}

// track mouse coordinates as it is the source of mass/gravity
var mouse = {
    x : -100,
    y : -100,
};

var effectRadius = 75;
var twirlAngle   = 90;

function draw(e) {
    context.clearRect(0, 0, canvas.width, canvas.height);
    
    particles.forEach(function (particle) {
        // move the particle to its original position
        particle.position.affected = Object.create(particle.position.actual);
        
        // calculate the effect area
        var a = mouse.y - particle.position.actual.y;
        var b = mouse.x - particle.position.actual.x;
        var dist = Math.sqrt(a*a + b*b);
        
        // check if the particle is in the affected area
        if (dist < effectRadius) {
            
            // angle of the particle relative to the mouse
            var a = angle(mouse.x, mouse.y, particle.position.actual.x, particle.position.actual.y);
            
            var strength = twirlAngle - easeOutQuad(dist, 0, twirlAngle, effectRadius);
            
            // twirl
            a += strength;
            
            // new position for the particle that's affected by gravity
            var p = rotate(a, dist, mouse.x, mouse.y);
            
            particle.position.affected.x = p.x;
            particle.position.affected.y = p.y;
        }
        
        context.beginPath();
        context.rect(particle.position.affected.x-1, particle.position.affected.y-1, 2, 2);
        context.fillStyle = "black";
        context.fill();
    });
}

draw();

window.addEventListener("mousemove", function (e) {
    mouse.x = e.x - canvas.offsetLeft;
    mouse.y = e.y - canvas.offsetTop;
    requestAnimationFrame(draw);
});

function easeOutQuad(t, b, c, d) {
    t /= d;
    return -c * t*(t-2) + b;
};

function angle(originX, originY, targetX, targetY) {
    var dx = targetX - originX;
    var dy = targetY - originY;
    var theta = Math.atan2(dy, dx) * (180 / Math.PI);
    if (theta < 0) theta = 360 + theta;
    return theta;
}

Number.prototype.map = function (in_min, in_max, out_min, out_max) {
    return (this - in_min) / (in_max - in_min) * (out_max - out_min) + out_min;
};

function pos(x, y, angle, length) {
    angle *= Math.PI / 180;
    return {
        x : Math.round(x + length * Math.cos(angle)),
        y : Math.round(y + length * Math.sin(angle)),
    };
}

function rotate(angle, distance, originX, originY) {
    return {
        x : originX + Math.cos(angle * Math.PI/180) * distance,
        y : originY + Math.sin(angle * Math.PI/180) * distance,
    }
}
* {
  margin: 0;
  padding: 0;
  box-sizing: inherit;
  line-height: inherit;
  font-size: inherit;
  font-family: inherit;
}

body {
  font-family: sans-serif;
  box-sizing: border-box;
  background-color: hsl(0, 0%, 90%);
}

canvas {
  display: block;
  background: white;
  box-shadow: 0 0 2px rgba(0, 0, 0, .2), 0 1px 1px rgba(0, 0, 0, .1);
  margin: 20px auto;
}
<canvas id="canvas"></canvas>


来源：https://stackoverflow.com/questions/33402497/pinch-pucker-an-image-in-canvas

标签
javascript
canvas
geometry
distortion
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