HTML5 Canvas 4 条线，每个线点都有渐变

Question

自从我从 canvas 开始，我已经想出了如何制作菱形，但现在我需要从每个角开始使用自定义渐变来放置菱形

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext('2d');
var grd= ctx.createRadialGradient(0,0,1,0,0,150);

grd.addColorStop(0, "#ff737b");
grd.addColorStop(1, "#f78c21");

ctx.moveTo(25, 25); //1ª ponto esquerda
ctx.lineTo(100, 0); //2º ponto para direita
ctx.lineTo(75, 75); //3º ponto para baixo
ctx.lineTo(25, 75); //4º ponto para esquera
ctx.closePath();
ctx.fillStyle = grd;
ctx.fill();

<canvas id="myCanvas">Your browser does not support the HTML5 canvas tag.</canvas>

我需要这样的图片

颜色是：

TopLeft = #ce2908
TopRight = #5a6bc6
BottomRight = #8c3173
BottomLeft = #f78c21

Answer 1

我会这样做：

创建4个linearGradients，对应你的top-left,top-right,bottom -右 和 左下角 角。
让它们都停在中间点（这里50,50）。
将它们最终的stop-color改为rgba中对应的值，alpha设置为0.1这样，中心点几乎是透明的，所有中间颜色都会混合在一起。

注：
为了避免形状一般透明，可以先在它下面画一个白色的形状。为了让所有形状完全透明，将它们的第一个停止颜色更改为 rgba(r,g,b,0.8).

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

var topLeft= ctx.createLinearGradient(25,25,50,50);
topLeft.addColorStop(0, "rgba(140, 49, 115, 1)");
topLeft.addColorStop(1, "rgba(140, 49, 115, .1)");

var topRight= ctx.createLinearGradient(100,25,50,50);
topRight.addColorStop(0, "rgba(90, 107, 198, 1)");
topRight.addColorStop(1, "rgba(90, 107, 198, .1)");

var bottomRight= ctx.createLinearGradient(75,75,50,50);
bottomRight.addColorStop(0, "rgba(247, 140, 33, 1)");
bottomRight.addColorStop(1, "rgba(247, 140, 33, .1)");

var bottomLeft= ctx.createLinearGradient(25,75,50,50);
bottomLeft.addColorStop(0, "rgba(206, 41, 8, 1)");
bottomLeft.addColorStop(1, "rgba(206, 41, 8, .1)");

ctx.beginPath();
ctx.moveTo(25, 25); //1ª ponto esquerda
ctx.lineTo(100, 0); //2º ponto para direita
ctx.lineTo(75, 75); //3º ponto para baixo
ctx.lineTo(25, 75); //4º ponto para esquera

/* // Uncomment to avoid transparency in the middle
  ctx.fillStyle = "#FFF";
  ctx.fill();
*/

ctx.fillStyle = bottomRight;
ctx.fill();
ctx.fillStyle = bottomLeft;
ctx.fill();
ctx.fillStyle = topLeft;
ctx.fill();
ctx.fillStyle = topRight;
ctx.fill();

<canvas id="myCanvas">Your browser does not support the HTML5 canvas tag.</canvas>

HTML5 Canvas 4 条线，每个线点都有渐变

HTML5 Canvas 4 Lines with gradient on each line point

javascript

canvas

html5-canvas