Question

in Android I would like to draw a PieChart with a dynamically number of pies. Each pie should have a different color from a gradient.

For example I would like to have a gradient from light brown to dark brown. If I need to draw five pies, I need five volors from the start to the end of this gradient.

How can I do that in Java with the Android framework?

I found out that I can create a LinearGradient for a line, i.e.:

LinearGradient lg = new LinearGradient(1, 1, 5, 5, toRGB("lightbrown"), toRGB("darkbrown"), TileMode.REPEAT);

But I did not found any function to get a color from this line, i.e.:

// for the five needed RGB colors from the gradient line
lg.getRGBColor(1, 1);
lg.getRGBColor(2, 2);
lg.getRGBColor(3, 3);
lg.getRGBColor(4, 4);
lg.getRGBColor(5, 5);

Do you have any ideas how I can get this?

Thanks!

Answer 1

You cannot get these values directly from the LinearGradient. The gradient doesn’t contain the actual drawing. To get these values, you can paint them to a canvas and pull the colors out of the canvas, or what I’d suggest would be to calculate the values yourself.

It’s a repeating linear gradient in five steps and you have the RGB values for the first and last color. The rest is just math. Here’s the pseudo code:

int r1 = startColor.red;
int g1 = startColor.green;
int b1 = startColor.blue;

int r2 = endColor.red;
int g2 = endColor.green;
int b2 = endColor.blue;

int redStep = r2 - r1 / 4;
int greenStep = g2 - g1 / 4;
int blueStep = b2 - b1 / 4;

firstColor = new Color(r1, g1, b1);
secondColor = new Color(r1 + redStep, g1 + greenStep, b1 + blueStep);
thirdColor = new Color(r1 + redStep * 2, g1 + greenStep * 2, b1 + blueStep * 2);
fourthColor = new Color(r1 + redStep * 3, g1 + greenStep * 3, b1 + blueStep * 3);
fifthColor = new Color(r1 + redStep * 4, g1 + greenStep * 4, b1 + blueStep * 4);