android color between two colors, based on percentage?

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悲哀的现实
悲哀的现实 2020-11-29 23:17

I would like to calculate the color depending on a percentage value:

float percentage = x/total;
int color;
if (percentage >= 0.95) {
  color = Color.GREE         


        
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  • 2020-11-29 23:53

    Here are 2 ways to interpolate:

    private static float interpolate(final float a, final float b, final float proportion) {
        return a + (b - a) * proportion;
    }
    
    /** Returns an interpoloated color, between <code>a</code> and <code>b</code> */
    public static int interpolateColorHsv(final int a, final int b, final float proportion) {
        final float[] hsva = new float[3];
        final float[] hsvb = new float[3];
        Color.colorToHSV(a, hsva);
        Color.colorToHSV(b, hsvb);
        for (int i = 0; i < 3; ++i) {
            hsvb[i] = interpolate(hsva[i], hsvb[i], proportion);
        }
        return Color.HSVToColor(hsvb);
    }
    
    public static int interpolateRGB(final int colorA, final int colorB, final float bAmount) {
        final float aAmount = 1.0f - bAmount;
        final int red = (int) (Color.red(colorA) * aAmount + Color.red(colorB) * bAmount);
        final int green = (int) (Color.green(colorA) * aAmount + Color.green(colorB) * bAmount);
        final int blue = (int) (Color.blue(colorA) * aAmount + Color.blue(colorB) * bAmount);
        return Color.rgb(red, green, blue);
    }
    
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  • 2020-11-29 23:54

    Here is a pseudocode function that interpolates linearly between 2 colors (staying in RGB space). I'm using a class called Color here instead of ints for clarity.

    bAmount is between 0 and 1 (for interpolation)

    Color interpolate(Color colorA, Color colorB, float bAmount) {
        Color colorOut;
        float aAmount = 1.0 - bAmount;
        colorOut.r =  colorA.r * aAmount + colorB.r * bAmount;
        colorOut.g =  colorA.g * aAmount + colorB.g * bAmount;
        colorOut.b =  colorA.b * aAmount + colorB.b * bAmount;
        return colorOut;
    }
    
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  • 2020-11-29 23:58

    Ok, after 2 hours of converting to yuv, hsv, etc pp... I give up. I now do it just like this:

    public class ColorUtils {
        private static int FIRST_COLOR = Color.GREEN;
        private static int SECOND_COLOR = Color.YELLOW;
        private static int THIRD_COLOR = Color.RED;
    
        public static int getColor(float p) {
            int c0;
            int c1;
            if (p <= 0.5f) {
                p *= 2;
                c0 = FIRST_COLOR;
                c1 = SECOND_COLOR;
            } else {
                p = (p - 0.5f) * 2;
                c0 = SECOND_COLOR;
                c1 = THIRD_COLOR;
            }
            int a = ave(Color.alpha(c0), Color.alpha(c1), p);
            int r = ave(Color.red(c0), Color.red(c1), p);
            int g = ave(Color.green(c0), Color.green(c1), p);
            int b = ave(Color.blue(c0), Color.blue(c1), p);
            return Color.argb(a, r, g, b);
        }
    
        private static int ave(int src, int dst, float p) {
            return src + java.lang.Math.round(p * (dst - src));
        }
    }
    

    By explicity using yellow as the middle color, the generated colors are brighter :-)

    Anyway.. if someone has a good other solution, I would appreciate it.

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