CODEWITHSUNDEEP
c#colorsgradient
mafu
mafu

Reputation: 32650

How do I get a rainbow color gradient in C#?

I'd like to have an enumeration of Colors based on the rainbow colors (red... yellow... green... blue...).

I see basically two ways to do that:

  1. Create a lookup table containing some important reference colors and interpolate between these. I don't like this idea at all.

  2. Apply some more or less fancy math. Probably less, but I don't quite see how it works. Any ideas?

(Oh, and while I did some SO research, I found no good results. If this question was already posted, please just point me to the location and I'll delete this.)

Edit: I'd prefer to have this independent of the used technology to display the gradient. For instance, something like GetRainbowColor (float f) with f ranging from 0 (red) to 1 (violet) would work great.

Upvotes: 20

Views: 42576

Answers (8)

Elmue
Elmue

Reputation: 8148

I see so many code samples which use doubles. But R,G,B are bytes, so it makes no sense to use doubles.

By the way: there are only 1536 possible colors when you sweep through all possible rainbow colors with 0...255 for each color.

Each of the 3 colors sweeps up and down = 6 sweeps. The maximum colors you get with this algorithm are 6 * 256 = 1536 colors.

Any formulas that you find here which produce more colors than 1536 will contain repeating colors!

The following algorithm works only with integers.

/// <summary>
/// s32_Sweeps = 4 --> Colors from blue to red, not including magenta       (1024 colors)
/// s32_Sweeps = 6 --> Complete sweep with all rainbow colors, also magenta (1536 colors)
/// </summary>
private static Color[] CalcRainbow(int s32_Sweeps)
{
    Color[] c_Colors = new Color[s32_Sweeps * 256];
    int R,G,B,P=0;
    for (int L=0; L<s32_Sweeps; L++)
    {
        for (int E=0; E<256; E++)
        {
            switch (L)
            {
                case 0: R = 0;       G = E;       B = 255;     break; // Blue...Cyan
                case 1: R = 0;       G = 255;     B = 255 - E; break; // Cyan...Green
                case 2: R = E;       G = 255;     B = 0;       break; // Green...Yellow
                case 3: R = 255;     G = 255 - E; B = 0;       break; // Yellow...Red
                case 4: R = 255;     G = 0;       B = E;       break; // Red...Magenta
                case 5: R = 255 - E; G = 0;       B = 255;     break; // Magenta...Blue
                default: throw new ArgumentException();
            }
            c_Colors[P++] = Color.FromArgb(255, R, G, B);
        }
    }
    return c_Colors;
}

Upvotes: 2

TiMoFey
TiMoFey

Reputation: 1

uint32_t Wheel(byte WheelPos) { // 0 - 255 return unit32_t
  if(WheelPos < 85) {
   return strip.Color(WheelPos * 3, 255 - WheelPos * 3, 0); //red + green
  } else if(WheelPos < 170) {
   WheelPos -= 85;
   return strip.Color(255 - WheelPos * 3, 0, WheelPos * 3); //blue + red
  } else {
   WheelPos -= 170;
   return strip.Color(0, WheelPos * 3, 255 - WheelPos * 3); //green + blue
  }
}

if wheelpos == 5, it return (15, 240, 0)

6 = (18, 237, 0)

Upvotes: 0

Peter Parker
Peter Parker

Reputation: 1

Just use the Rainbow.dll. This is probably not the best library, but for a smooth Rainbow effect on, I think, every WinForm Control you want, this is it.

Link: https://marschalldev.com/2018/08/02/csharp-rainbow-effect-net-dll/

How to use: Yourcontrol.background = Color.FromArgb(Class1.A, Class1.R, Class1.G);

Upvotes: -2

0x59
0x59

Reputation: 87

http://colorfulconsole.com/ Allows pretty much what you're looking for, also can be installed as a NuGet package. It's not exactly a rainbow gradient. But it can write gradients to the console, also this confuses the IDE between the 

Colorful.Console

and

System.Console

So make sure to define the right Console.

Upvotes: 0

ProfNimrod
ProfNimrod

Reputation: 4310

Here's one I like to use (the output is an HTML RGB color):

public static String Rainbow(Int32 numOfSteps, Int32 step)
        {
            var r = 0.0;
            var g = 0.0;
            var b = 0.0;
            var h = (Double)step / numOfSteps;
            var i = (Int32)(h * 6);
            var f = h * 6.0 - i;
            var q = 1 - f;

            switch (i % 6)
            {
                case 0:
                    r = 1;
                    g = f;
                    b = 0;
                    break;
                case 1:
                    r = q;
                    g = 1;
                    b = 0;
                    break;
                case 2:
                    r = 0;
                    g = 1;
                    b = f;
                    break;
                case 3:
                    r = 0;
                    g = q;
                    b = 1;
                    break;
                case 4:
                    r = f;
                    g = 0;
                    b = 1;
                    break;
                case 5:
                    r = 1;
                    g = 0;
                    b = q;
                    break;
            }
            return "#" + ((Int32)(r * 255)).ToString("X2") + ((Int32)(g * 255)).ToString("X2") + ((Int32)(b * 255)).ToString("X2");
        }

Upvotes: 3

Bitterblue
Bitterblue

Reputation: 14085

I like to use this:

public static Color Rainbow(float progress)
{
    float div = (Math.Abs(progress % 1) * 6);
    int ascending = (int) ((div % 1) * 255);
    int descending = 255 - ascending;

    switch ((int) div)
    {
        case 0:
            return Color.FromArgb(255, 255, ascending, 0);
        case 1:
            return Color.FromArgb(255, descending, 255, 0);
        case 2:
            return Color.FromArgb(255, 0, 255, ascending);
        case 3:
            return Color.FromArgb(255, 0, descending, 255);
        case 4:
            return Color.FromArgb(255, ascending, 0, 255);
        default: // case 5:
            return Color.FromArgb(255, 255, 0, descending);
    }
}

Upvotes: 9

Mike Two
Mike Two

Reputation: 46173

In winforms(or anything using GDI+) you could use System.Drawing.Drawing2D.LinearGradientBrush to do the interpolation for you.

WPF's System.Windows.Media.GradientBrush could work as well. It's abstract so you might end up with WPF's LinearGradientBrush. It's in a different namespace than the other.

EDIT: since the question was edited to indicate that you want to be tech independent I don't think this answer applies. I'm going to leave it here for now in case someone is looking for Gradients in C#, but if someone finds that objectionable I'll remove the answer.

I did a quick check to see if you could at least get at some of the functionality in a more independent way (such as getting an array of Point or something). Doesn't appear to be the case.

Upvotes: 2

Brian R. Bondy
Brian R. Bondy

Reputation: 347256

This is easier than you think.

First you need an hsv or hsl to rgb conversion function. Here is C# code to do that conversion.

Then you simply iterate over all of the possible values of the hue h while keeping the saturation s and luminosity l constant.

If you want 100 colors of the rainbow spaced out equally:

for(double i = 0; i < 1; i+=0.01)
{
    ColorRGB c = HSL2RGB(i, 0.5, 0.5);
    //do something with the color
}

You could also easily create your desired function GetRainbowColor this way by adding all of these colors to a List<ColorRGB> and returning the appropriate indexed color.

Upvotes: 34

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