//Code created by @Mr_Nauta and posted in http://codenauta.blogspot.com
//If you have any question please ask me in a comment or ask me in my Twitter: @Mr_Nauta
//You can use this code in your project but I like that I will appear in credits or thanks :)

using UnityEngine;
using System.Collections;

public class GradientBar : MonoBehaviour {
 private Texture2D bar_tex;//This is the texture of the progress bar

 int c=100;//This variable is only for testing, while is pressed space key it will decreased by 1 (see Update() function)

 void Start () {
  //Create a new texture (100 width, 1 height)
  bar_tex = new Texture2D (100, 1);
  //With these options the texture will be automatically resized without code
  bar_tex.filterMode = FilterMode.Bilinear;
  bar_tex.wrapMode = TextureWrapMode.Clamp;
  //Apply changes in the texture
  bar_tex.Apply();
  //And set this texture as the main texture of our progress bar (a basic plane object)
  renderer.material.mainTexture = bar_tex;
 }

 //This function is only used for testing and can be deleted
 void Update () {
  //If is pressed the space key...
  if (Input.GetKey("space")) {
   //If c is more than 100...
   if(c>100)
    //We set it to 100
    c=100;
   //If c is between 100 and 0...
   if((c<=100)&&(c>-1)){
    //Set pixel at coordinates c,1 (c is the width and 1 the height (height is constant because our texture is only 1 of height))
    bar_tex.SetPixel(c,1,GetBlendedColor(c));//GetBlendedColor is our main function and only need the percentage of the progress bar in base 100 like 9% or 21%
    bar_tex.Apply(); //Apply changes
    c--;//And decrese by 1 c variable
   }
  }
 }
 public Color GetBlendedColor(int percentage){
  //If percentage is less than 50
  if (percentage < 50) {
   //Call interpolate function between colors green and yellow, and parsing the total percentage of the progress bar to a custom percentage (see our TransfromPercentage function for more info)
   return Interpolate(Color.green,Color.yellow,TransformPercentage(percentage));
  } else {
   //If is more than 50 call interpolate function with colors yellow and red
   return Interpolate(Color.red,Color.yellow,TransformPercentage(100-percentage));
  }
 }
 public float TransformPercentage(int p){
  //This function divide our 100 per 100 progress bar in 2 "virtual" progress bar:
  //-> 1 progress bar of 100 point between 0 and 50
  //-> Other progress bar of 100 point between 50 and 100
  //And also transform that value in a float value, transforming the value from base 100 to base 1, for example:
  //In our 100 per 100 progress bar we have this percentage: 23%
  //Our final value will be: (23/100.0)*2.0
  //Other example, in our 100 per 100 progress bar we have this percentage: 86%
  //Our final value will be: ((100-86)/100.0)*2.0
  return (float)((p / 100f) * 2f);
 }
 public Color Interpolate(Color c1,Color c2,float p){
  //This function use a Unity function called color lerp that need three arguments;
  //c1 and c2 (interpolated colors)
  //p The percentage of interpolation in our situation
  return Color.Lerp(c1,c2,p);
 }
}