Question

我试着谷歌搜索答案，但我从来没有找到一个简单的答案，或为什么答案有效。所以我想知道，用什么代码来改变画布上图像的颜色？例如，假设我想将内容更改为#ff0000。如果像素为#000000，则应该保持这种状态。如果像素为#ffffff，则应为#ff0000。这是我的文本对象构造函数：

Text = function(x, y, str, s, c){
        var img = new Image();
        img.src = "font.png";
        var alphabet = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", ".", "!", "?"]
        this.text = str.toLowerCase();
        this.x = x;
        this.y = y;
        this.type = "text";
        this.rows = 1;
        this.height = this.rows * 10;
        this.width = this.text.length * 8;
        this.draw = function(){
            for (var i = 0; i < this.text.length; i++)
            {
                scene.ctx.drawImage(img, (alphabet.indexOf(this.text[i]) % 16) * 8, Library.newMath.roundZero(alphabet.indexOf(this.text[i]) / 16) * 10, 8, 10, this.x + i * 8 + (scene.xOffset * !this.fixed), this.y + 0 + (scene.yOffset * !this.fixed), 8, 10);
            }           
        }
        Shape.prototype.constructor.call(this, x, y);
    }

Answer 1

markE为您提供了实现所需内容的全部密钥in comments，但此处适用于您的案例：

您说您的图片只有一种纯色，白色 ^{（这里我会考虑透明没有颜色，但在其他情况下它是）}
要更改此颜色，您可以使用ctx.globalCompositeOperation('source-atop')参数，该参数将“仅在与现有画布内容重叠的位置”绘制新形状。这意味着您可以先绘制字母形状，然后在其上填充一个矩形，并且只绘制彩色字母形状。

var ctx = canvas.getContext('2d');
var img = new Image();
img.onload = function() {
  canvas.width = this.width;
  canvas.height = this.height;
  ctx.fillStyle = 'red';
  ctx.drawImage(this, 0, 0);
  ctx.globalCompositeOperation = 'source-atop';
  ctx.fillRect(0, 0, canvas.width, canvas.height)
    // reset to default
  ctx.globalCompositeOperation = 'source-over';
}
img.src = "http://i.stack.imgur.com/9RQXh.png";

<canvas id="canvas"></canvas>

或者您可以采用其他方式：首先绘制彩色矩形，将globalCompositeOperation设置为"destination-atop"，然后绘制您的信件。

var ctx = canvas.getContext('2d');
var img = new Image();
img.onload = function() {
  canvas.width = this.width;
  canvas.height = this.height;
  ctx.fillStyle = 'red';
  ctx.fillRect(0, 0, canvas.width, canvas.height)
  ctx.globalCompositeOperation = 'destination-atop';
  ctx.drawImage(this, 0, 0);
  // reset to default
  ctx.globalCompositeOperation = 'source-over';
}
img.src = "http://i.stack.imgur.com/9RQXh.png";

<canvas id="canvas"></canvas>

现在，要在代码中实现它，您可以保存Text对象中设置的彩色字母并绘制它而不是原始图像：

Text = function(x, y, str, s, c){
    var img = new Image();
    // save a pointer to our object so we can use it in the onload event
    var that = this;
    // here implement the coloring part
    img.onload = function(){
      that.img = document.createElement('canvas');
      that.img.width = this.width;
      that.img.height = this.height;
      var ctx = that.img.getContext('2d');
      // set the color to the wanted one
      ctx.fillStyle = c;
      ctx.fillRect(0, 0, canvas.width, canvas.height)
      ctx.globalCompositeOperation = 'destination-atop';
      ctx.drawImage(this, 0, 0);
      }
    img.src = "font.png";
    var alphabet = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", ".", "!", "?"]
    this.text = str.toLowerCase();
    this.x = x;
    this.y = y;
    this.type = "text";
    this.rows = 1;
    this.height = this.rows * 10;
    this.width = this.text.length * 8;
    this.draw = function(){
        for (var i = 0; i < this.text.length; i++)
        {
            // here use the canvas we created
            scene.ctx.drawImage(this.img, (alphabet.indexOf(this.text[i]) % 16) * 8, Library.newMath.roundZero(alphabet.indexOf(this.text[i]) / 16) * 10, 8, 10, this.x + i * 8 + (scene.xOffset * !this.fixed), this.y + 0 + (scene.yOffset * !this.fixed), 8, 10);
        }           
    }
    Shape.prototype.constructor.call(this, x, y);
}

更改画布上图像的颜色/色调的最佳方法是什么？

1 个答案: