Html5 Canvas Gradients

Html5 Canvas Gradients

Just like in CSS, you can create gradients in html5 canvas, too. If you couldn’t, I wouldn’t be that impressed with it. It would definitely be a feature that would be requested. Even though flat is in right now, everyone likes the ability to created the added touch of a slight gradient. However, just like in CSS, gradients can be a little tough to master, but with this tutorial, I’ll break down how html5 canvas gradients.

Gradients can be used to fill most shapes, such as rectangles, circles, lines, text, etc. Shapes on the canvas are not limited to solid colors (thank goodness). I really think it is interesting that you can apply gradients to lines, considering it took forever to get that feature added to Adobe Illustrator, and it’s an advanced vector program. Just like in Photoshop or Illustrator, there are 2 different types of gradients.

createLinearGradient(x,y,x1,y1) – Creates a linear gradient

createRadialGradient(x,y,r,x1,y1,r1) – Creates a radial gradient

Create Your Shape: Then add color stops

Once we have a gradient object, we must add two or more color stops. This is like in Photoshop or Illustrator, when you create a custom gradient starting with one color, and ending with another. Photoshop and Illustrator determine the transition between the two, while you determine the main 2 colors that you’re blending. It works this way with html5 canvas gradients, but you specify those main 2 colors with javascript.

The addColorStop() method specifies the color stops, and its position on the gradient. Gradient positions can be anything from 0 to 1.

To use the gradient, you have to use the fillStyle or strokeStyle property with the gradient, and then draw the shape, like a rectangle, circle, text, or line.

Html5 Canvas Gradients: Linear

Create a linear gradient. Fill  the rectangle with the gradient:

<canvas id="myCanvas" width="200" height="100" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

<script>

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

// Create gradient
var grd=ctx.createLinearGradient(0,0,200,0);
grd.addColorStop(0,"green");
grd.addColorStop(1,"blue");

// Fill with gradient
ctx.fillStyle=grd;
ctx.fillRect(10,10,150,80);

</script>
Result:
html5 canvas gradient: linear
Just like in Photoshop and Illustrator, you can have more that 2 colors in a gradient. Keeping with our example, if you add:
grd.addColorStop(.4,”red”);
between our existing 2 gradients in the javascript, you get the result below.
html5 canvas gradients: multiple color stops

Html5 Canvas Gradients: Radial

Create a radial/circular gradient. Fill rectangle with the gradient:

<canvas id="myCanvas" width="200" height="100" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

<script>

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

// Create gradient
var grd=ctx.createRadialGradient(75,50,5,90,60,100);
grd.addColorStop(.0,"green");
grd.addColorStop(1,"blue");

// Fill with gradient
ctx.fillStyle=grd;
ctx.fillRect(10,10,150,80);

</script>

Result:

html5 canvas gradients: radial

Changing the value of the green color stop from 0 to .5 makes the transition more harsh.

html5 canvas gradients: radial 2

Html5 Canvas Gradients: Conslusion

Html5 canvas gradients work in a similar way to Photoshop and Illustrator gradients, you’re just using javascript instead of slider controls. Learning how different aspects of the javascript affect the outcome of your gradients can help you to render html5 canvas art more accurately and with better precision.

Were you able to successfully create html5 canvas gradients? If you have any questions, or anything you’d like to add, feel free to leave your thoughts in the comments section below.

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