HTML5画布涂料混色工具

Question

您好我需要创建混合颜色工具，我尝试使用getImageData从画布中获取颜色像素并混合我选择的颜色并获得平均颜色，我可以轻松获得：

/* 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);

虽然我画画时尝试混合这种颜色，但混合效果不可用..

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

我需要该工具可以在左侧获取图像：

Answer 1

您没有说明足够的细节，但以下是如何将混合模式与画布一起使用。请注意，IE还不支持其中任何一个（normal除外），因此请在最近的Firefox或Chrome中对此进行测试。

当前修订的画布标准中的所有混合模式都列在可用于选择模式的下拉列表中。通过这种方式，您可以查看哪种模式最适合您的需求（尝试使用低{alpha值）的hard-light作为开头......）。

（是的，我感到无聊.. :)）

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>