Use premultiplied alpha for all textures and blending.

OpenRA.Mods.Common/Traits/World/PaletteFromPaletteWithAlpha.cs

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+#region Copyright & License Information
+/*
+ * Copyright 2007-2015 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Drawing;
+using OpenRA.Graphics;
+using OpenRA.Mods.Common.Traits;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.D2k.Traits
+{
+	[Desc("Create a palette by applying alpha transparency to another palette.")]
+	class PaletteFromPaletteWithAlphaInfo : ITraitInfo
+	{
+		[Desc("Internal palette name")]
+		public readonly string Name = null;
+
+		[Desc("The name of the palette to base off.")]
+		public readonly string BasePalette = null;
+
+		[Desc("Allow palette modifiers to change the palette.")]
+		public readonly bool AllowModifiers = true;
+
+		[Desc("Alpha component that is applied to the base palette.")]
+		public readonly float Alpha = 1.0f;
+
+		[Desc("Premultiply color by the alpha component.")]
+		public readonly bool Premultiply = true;
+
+		public object Create(ActorInitializer init) { return new PaletteFromPaletteWithAlpha(this); }
+	}
+
+	class PaletteFromPaletteWithAlpha : ILoadsPalettes, IProvidesAssetBrowserPalettes
+	{
+		readonly PaletteFromPaletteWithAlphaInfo info;
+
+		public PaletteFromPaletteWithAlpha(PaletteFromPaletteWithAlphaInfo info) { this.info = info; }
+
+		public void LoadPalettes(WorldRenderer wr)
+		{
+			var remap = new AlphaPaletteRemap(info.Alpha, info.Premultiply);
+			wr.AddPalette(info.Name, new ImmutablePalette(wr.Palette(info.BasePalette).Palette, remap), info.AllowModifiers);
+		}
+
+		public IEnumerable<string> PaletteNames { get { yield return info.Name; } }
+	}
+
+	class AlphaPaletteRemap : IPaletteRemap
+	{
+		readonly float alpha;
+		readonly bool premultiply;
+
+		public AlphaPaletteRemap(float alpha, bool premultiply)
+		{
+			this.alpha = alpha;
+			this.premultiply = premultiply;
+		}
+
+		public Color GetRemappedColor(Color original, int index)
+		{
+			var a = (int)(original.A * alpha).Clamp(0, 255);
+			var r = premultiply ? (int)(alpha * original.R + 0.5f).Clamp(0, 255) : original.R;
+			var g = premultiply ? (int)(alpha * original.G + 0.5f).Clamp(0, 255) : original.G;
+			var b = premultiply ? (int)(alpha * original.B + 0.5f).Clamp(0, 255) : original.B;
+
+			return Color.FromArgb(a, r, g, b);
+		}
+	}
+}