javascript - HTML5 canvas paint 调色工具

Question

你好我需要创建混合颜色工具，我尝试使用 getImageData 从 Canvas 中获取颜色像素并与我选择的颜色混合并获得平均颜色，我可以轻松获得它:

/* r1 = red channel from getImageData
   g1 = green channel from getImageData
   b1 = blue channel from getImageData

   r2 = red channel my selected color
   g2,b2 same
*/   
var avR = Math.round(0.5*r1 + 0.5*r2);
var avG = Math.round(0.5*g1 + 0.5*g2);
var avB = Math.round(0.5*b1 + 0.5*b2);

虽然我画画我尝试混合这种颜色，但混合效果不可用..

也许有人可以帮助我？ http://jsfiddle.net/b72ky2sc/6/

我需要那个工具可以在左侧获取图像:

Answer 1

你没有说明足够的细节，但这里是你如何使用 Canvas 的混合模式。请注意，IE 尚不支持其中任何一个(normal 除外)，因此请在最新的 Firefox 或 Chrome 中进行测试。

当前修订的 Canvas 标准中的所有混合模式都列在下拉列表中，您可以使用它来选择模式。通过这种方式，您可以看到哪种模式最适合您的需要(尝试使用诸如 hard-light 之类的低 alpha 值作为开始...)。

(是的，我很无聊.. :))

var cont = document.getElementById("spots"),      // UI elements
    canvas = document.getElementById("canvas"),
    alpha = document.getElementById("alpha"),
    modes = document.getElementById("modes"),
    ctx = canvas.getContext("2d"),
    isDown = false,                               // defaults
    color = "rgb(107, 122, 174)";

// set up color palette using a custom "Spot" object
// This will use a callback function when it is clicked, to
// change current color
function Spot(color, cont, callback) {
  var div = document.createElement("div");
  div.style.cssText = "width:50px;height:50px;border:1px solid #000;margin:0 1px 1px 0;background:" + color;
  div.onclick = function() {callback(color)};
  cont.appendChild(div);    
}

// add some spot colors to our palette container
new Spot(color, cont, setColor);
new Spot("rgb(107, 174, 170)", cont, setColor);
new Spot("#00f", cont, setColor);
new Spot("#ff0", cont, setColor);
new Spot("#0ff", cont, setColor);
new Spot("#f0f", cont, setColor);

// this will set current fill style based on spot clicked
function setColor(c) {ctx.fillStyle = c}

// setup defaults
ctx.fillStyle = color;
ctx.globalAlpha = 0.5;

// events
canvas.onmousedown = function() {isDown = true};
window.onmouseup = function() {isDown = false};
window.onmousemove = function(e) {
  if (!isDown) return;
  var r = canvas.getBoundingClientRect(),
      x = e.clientX - r.left,
      y = e.clientY - r.top;
  
  ctx.beginPath();
  ctx.arc(x, y, 25, 0, 2*Math.PI);
  ctx.fill();
};

alpha.onchange = function(){ctx.globalAlpha = alpha.value * 0.01};
modes.onchange = function(){ctx.globalCompositeOperation = modes.value};

body{font:14px sans-serif;background:#333;color:#eee}
#spots {float:right}
#canvas {background:#fff;cursor:crosshair;border:1px solid #777}

<label for="modes">Blending Modes:</label>
<select id="modes">
  <option value="normal">normal</option>
  <option value="multiply">multiply</option>
  <option value="screen">screen</option>
  <option value="overlay">overlay</option>
  <option value="darken">darken</option>
  <option value="lighten">lighten</option>
  <option value="color-dodge">color-dodge</option>
  <option value="color-burn">color-burn</option>
  <option value="hard-light">hard-light</option>
  <option value="soft-light">soft-light</option>
  <option value="difference">difference</option>
  <option value="exclusion">exclusion</option>
  <option value="hue">hue</option>
  <option value="saturation">saturation</option>
  <option value="color">color</option>
  <option value="luminosity">luminosity</option>
</select>
<label for="alpha">Alpha:</label><input id="alpha" type="range" min=0 max=100 value="50">
<br>
<canvas id="canvas" width=500 height=500></canvas><div id="spots"></div>