JavaScript

Search for '{{search_term}}'

SVG Linear Gradient

CMOS is the Code-Maven Open Source podcast that also includes video interviews. Subscribe to this feed RSS feed with your Podcast listener app or via iTunes iTunes.

This is part of the SVG Tutorial and exercises adding linear gradient to a rectangle in SVG.

Gradient is when in an area the color gradually changes from one color to another color. In this article we'll look at linear gradient when the color changes along a straight line. We are going to fill a rectangle shape using the changing color.

Normally, as you can see in the basic rectangle examples we can call the fill method, pass an RGB value to it and have it filled by that color. $shape->fill('#F0F0F0'). Alternatively we could call the attr method: $shape->attr({ 'fill' : '#F0F0F0' }).

Instead of a fix color, we can pass a gradient to the fill method, and let SVG fill the shape with that changing color.

White to Black top to bottom

In the first example we create a linear gradient using the gradient method. The first argument is just the string 'linear', the second argument is a function setting the color values at various points along a linear line going from 0 to 1. We can supply several colorts in that range, but we should supply at least the two end-points. If we only supply one color, SVG will use that single color to fill the whole shape. No gradient will be used. Getting back to our first example: we set the color to be '#FFF' (which is just a short-hand for '#FFFFFF') which is white at the begining of the 0-1 line. We also set the color to be '#000' (which is a short-hand for '#000000') which black at the end of the 0-1 line. The whole construct is assigned to an arbitrary variable we called gr.

We can then map the 0-1 line onto the corners of the rectangle. The from method connects the beginning of the 0-1 line to the coordinates (0, 0) of the rectangle that mark the top left corner. The to method connects the end of the 0-1 line to the coordinates (0, 1) of the rectangle that marks the bottom left corner. (Actualy in both the from and to methods the first number sets the horizontal side 0 being left 1 being right; the second coordinate sets the vertical side 0 being top, 1 being bottom.)

Once we configured our gradient, we can create a rectangle and use the variable gr that holds the gradient as the value of the fill attribute.

The stroke method is used to create a line around the rectangle. This helps us to see the edge of the rectangle.

examples/js/svg_rectangle_20.js
function rect_20() {
    var draw = SVG('rect_20');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#FFF');
        stop.at(1, '#000');
    });
    gr.from(0, 0).to(0, 1);
    var rect = draw.rect(200, 100).attr({ fill: gr }).stroke({ width: 1 });

}
rect_20();


White to Black corner to corner

In the next example I've changed two things. One is that we use the fill(gr) instead of attr({ 'fill' : gr }). This change does not have any impact on the result, I made it only to show that we can use either syntax.

The real change is that the gradient goes now from(0, 0) (left, top), to(1, 1) (right, bottom). If you look at the rectangle you'll see that the top left corner is white and the bottom right corner is black. Basically the 0-1 line of the gradiant was mapped to these two corners.

examples/js/svg_rectangle_21.js
function rect_21() {
    var draw = SVG('rect_21');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#FFF');
        stop.at(1, '#000');
    });
    gr.from(0, 0).to(1, 1);
    var rect = draw.rect(200, 100).fill(gr).stroke({ width: 1 });
}
rect_21();

3 stop gradient

In this example we got back to the horizontal lines as we had it in the first example, but instead of 2 stop points we now have 3. The two end-points are both 'black', but at the 0.25 of the 0-1 line, meaning at one quarter from the top of the rectangle, we have a white horizontal line. The color changes from black to white in the top quarter of the rectangle and then to black again in the lower 3/4 of the rectangle.

examples/js/svg_rectangle_22.js
function rect_22() {
    var draw = SVG('rect_22');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#000');
        stop.at(0.25, '#FFF');
        stop.at(1, '#000');
    });
    gr.from(0, 0).to(0, 1);
    var rect = draw.rect(200, 100).fill(gr).stroke({ width: 1 });

}
rect_22();

Blue gradient

In the next example we use a much smaller change in the gradient. This change in blue is pleasant to the eye. Starting with a lighter blue on the left side it becomes dark on the right hand side.

examples/js/svg_rectangle_27.js
function rect_27() {
    var draw = SVG('rect_27');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#1021A3');
        stop.at(1, '#A0A8EB');
    });
    gr.from(1, 0).to(0, 0);
    var rect = draw.rect(200, 100).fill(gr).stroke({ width: 1 });
}
rect_27();



4 directions

In the next 4 example you can see that the gradient can go between any two colors, in these cases the color changes from '#FF0000' which is red, to '#0000FF' which is blue.

The 4 examples differ in their direction. (The from is always (0, 0) but the to has 4 different values.) Notable might be the 4th example in which the value of to is the same as the value of from which causes the whole rectangle to be a single color. Not very useful.

examples/js/svg_rectangle_23.js

function rect_23() {
    var draw = SVG('rect_23');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#FF0000');
        stop.at(1, '#0000FF');
    });
    gr.from(0, 0).to(0, 1);
    var rect = draw.rect(200, 100).fill(gr).stroke({ width: 1 });
}
rect_23();


examples/js/svg_rectangle_24.js
function rect_24() {
    var draw = SVG('rect_24');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#FF0000');
        stop.at(1, '#0000FF');
    });
    gr.from(0, 0).to(1, 1);
    var rect = draw.rect(200, 100).fill(gr).stroke({ width: 1 });
}
rect_24();


examples/js/svg_rectangle_25.js
function rect_25() {
    var draw = SVG('rect_25');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#FF0000');
        stop.at(1, '#0000FF');
    });
    gr.from(0, 0).to(1, 0);
    var rect = draw.rect(200, 100).fill(gr).stroke({ width: 1 });
}
rect_25();


examples/js/svg_rectangle_26.js
function rect_26() {
    var draw = SVG('rect_26');
    draw.size(200, 100);

    var gr = draw.gradient('linear', function(stop) {
        stop.at(0, '#FF0000');
        stop.at(1, '#0000FF');
    });
    gr.from(0, 0).to(0, 0);
    var rect = draw.rect(200, 100).fill(gr).stroke({ width: 1 });
}
rect_26();



Comments

In the comments, please wrap your code snippets within <pre> </pre> tags and use spaces for indentation.
comments powered by Disqus