Apc variable charge bar color (#240)

* Make Apc chargebar color dependent on charge amount

* Adjust orange color and increase brightness

Content.Client/GameObjects/Components/Power/ApcBoundUserInterface.cs

@@ -3,12 +3,14 @@
 using NJsonSchema.Validation;
 using OpenTK.Graphics.OpenGL4;
 using Robust.Client.GameObjects.Components.UserInterface;
+using Robust.Client.Graphics.Drawing;
 using Robust.Client.Interfaces.Graphics;
 using Robust.Client.UserInterface;
 using Robust.Client.UserInterface.Controls;
 using Robust.Client.UserInterface.CustomControls;
 using Robust.Shared.GameObjects.Components.UserInterface;
 using Robust.Shared.IoC;
+using Robust.Shared.Maths;
 using Robust.Shared.Utility;
 
 namespace Content.Client.GameObjects.Components.Power
@@ -65,6 +67,45 @@ protected override void UpdateState(BoundUserInterfaceState state)
             }
 
             _chargeBar.Value = castState.Charge;
+            UpdateChargeBarColor(castState.Charge);
+        }
+
+        private void UpdateChargeBarColor(float charge)
+        {
+            float normalizedCharge = charge / _chargeBar.MaxValue;
+
+            float leftHue = 0.0f;// Red
+            float middleHue = 0.066f;// Orange
+            float rightHue = 0.33f;// Green
+            float saturation = 1.0f;// Uniform saturation
+            float value = 0.8f;// Uniform value / brightness
+            float alpha = 1.0f;// Uniform alpha
+
+            // These should add up to 1.0 or your transition won't be smooth
+            float leftSideSize = 0.5f;// Fraction of _chargeBar lerped from leftHue to middleHue
+            float rightSideSize = 0.5f;// Fraction of _chargeBar lerped from middleHue to rightHue
+
+            float finalHue;
+            if (normalizedCharge <= leftSideSize)
+            {
+                normalizedCharge /= leftSideSize;// Adjust range to 0.0 to 1.0
+                finalHue = FloatMath.Lerp(leftHue, middleHue, normalizedCharge);
+            }
+            else
+            {
+                normalizedCharge = (normalizedCharge - leftSideSize) / rightSideSize;// Adjust range to 0.0 to 1.0.
+                finalHue = FloatMath.Lerp(middleHue, rightHue, normalizedCharge);
+            }
+
+            // Check if null first to avoid repeatedly creating this.
+            if (_chargeBar.ForegroundStyleBoxOverride == null)
+            {
+                _chargeBar.ForegroundStyleBoxOverride = new StyleBoxFlat();
+            }
+
+            var foregroundStyleBoxOverride = (StyleBoxFlat)_chargeBar.ForegroundStyleBoxOverride;
+            foregroundStyleBoxOverride.BackgroundColor =
+                Color.FromHsv(new Vector4(finalHue, saturation, value, alpha));
         }
 
         protected override void Dispose(bool disposing)