rewrite content logic to decentralise cache (#488)

This is necessary due to changes in Stardew Valley 1.3, which now changes loaded assets and expects those changes to be persisted but not propagated to other content managers.

1 files changed, 617 insertions, 0 deletions

diff --git a/src/SMAPI/Framework/SContentManager.cs b/src/SMAPI/Framework/SContentManager.cs
new file mode 100644
index 00000000..8f008041
--- /dev/null
+++ b/src/SMAPI/Framework/SContentManager.cs
@@ -0,0 +1,617 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics.Contracts;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Content;
+using Microsoft.Xna.Framework.Graphics;
+using StardewModdingAPI.Framework.Content;
+using StardewModdingAPI.Framework.Exceptions;
+using StardewModdingAPI.Framework.Reflection;
+using StardewModdingAPI.Framework.Utilities;
+using StardewValley;
+
+namespace StardewModdingAPI.Framework
+{
+    /// <summary>A minimal content manager which defers to SMAPI's core content logic.</summary>
+    internal class SContentManager : LocalizedContentManager
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The central coordinator which manages content managers.</summary>
+        private readonly ContentCoordinator Coordinator;
+
+        /// <summary>The underlying asset cache.</summary>
+        private readonly ContentCache Cache;
+
+        /// <summary>Encapsulates monitoring and logging.</summary>
+        private readonly IMonitor Monitor;
+
+        /// <summary>A lookup which indicates whether the asset is localisable (i.e. the filename contains the locale), if previously loaded.</summary>
+        private readonly IDictionary<string, bool> IsLocalisableLookup;
+
+        /// <summary>The language enum values indexed by locale code.</summary>
+        private readonly IDictionary<string, LocalizedContentManager.LanguageCode> LanguageCodes;
+
+        /// <summary>The assets currently being intercepted by <see cref="IAssetLoader"/> instances. This is used to prevent infinite loops when a loader loads a new asset.</summary>
+        private readonly ContextHash<string> AssetsBeingLoaded = new ContextHash<string>();
+
+        /// <summary>The path prefix for assets in mod folders.</summary>
+        private readonly string ModContentPrefix;
+
+        /// <summary>Interceptors which provide the initial versions of matching assets.</summary>
+        private IDictionary<IModMetadata, IList<IAssetLoader>> Loaders => this.Coordinator.Loaders;
+
+        /// <summary>Interceptors which edit matching assets after they're loaded.</summary>
+        private IDictionary<IModMetadata, IList<IAssetEditor>> Editors => this.Coordinator.Editors;
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>A name for the mod manager. Not guaranteed to be unique.</summary>
+        public string Name { get; }
+
+        /// <summary>Whether this content manager is wrapped around a mod folder.</summary>
+        public bool IsModFolder { get; }
+
+        /// <summary>The current language as a constant.</summary>
+        public LocalizedContentManager.LanguageCode Language => this.GetCurrentLanguage();
+
+        /// <summary>The absolute path to the <see cref="ContentManager.RootDirectory"/>.</summary>
+        public string FullRootDirectory => Path.Combine(Constants.ExecutionPath, this.RootDirectory);
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="name">A name for the mod manager. Not guaranteed to be unique.</param>
+        /// <param name="serviceProvider">The service provider to use to locate services.</param>
+        /// <param name="rootDirectory">The root directory to search for content.</param>
+        /// <param name="currentCulture">The current culture for which to localise content.</param>
+        /// <param name="coordinator">The central coordinator which manages content managers.</param>
+        /// <param name="monitor">Encapsulates monitoring and logging.</param>
+        /// <param name="reflection">Simplifies access to private code.</param>
+        /// <param name="isModFolder">Whether this content manager is wrapped around a mod folder.</param>
+        public SContentManager(string name, IServiceProvider serviceProvider, string rootDirectory, CultureInfo currentCulture, ContentCoordinator coordinator, IMonitor monitor, Reflector reflection, bool isModFolder)
+                : base(serviceProvider, rootDirectory, currentCulture)
+        {
+            // init
+            this.Name = name;
+            this.IsModFolder = isModFolder;
+            this.Coordinator = coordinator ?? throw new ArgumentNullException(nameof(coordinator));
+            this.Cache = new ContentCache(this, reflection);
+            this.Monitor = monitor ?? throw new ArgumentNullException(nameof(monitor));
+            this.ModContentPrefix = this.GetAssetNameFromFilePath(Constants.ModPath, ContentSource.GameContent);
+
+            // get asset data
+            this.LanguageCodes = this.GetKeyLocales().ToDictionary(p => p.Value, p => p.Key, StringComparer.InvariantCultureIgnoreCase);
+            this.IsLocalisableLookup = reflection.GetField<IDictionary<string, bool>>(this, "_localizedAsset").GetValue();
+
+        }
+
+        /// <summary>Load an asset that has been processed by the content pipeline.</summary>
+        /// <typeparam name="T">The type of asset to load.</typeparam>
+        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
+        public override T Load<T>(string assetName)
+        {
+            return this.Load<T>(assetName, LocalizedContentManager.CurrentLanguageCode);
+        }
+
+        /// <summary>Load an asset that has been processed by the content pipeline.</summary>
+        /// <typeparam name="T">The type of asset to load.</typeparam>
+        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
+        /// <param name="language">The language code for which to load content.</param>
+        public override T Load<T>(string assetName, LanguageCode language)
+        {
+            // normalise asset key
+            this.AssertValidAssetKeyFormat(assetName);
+            assetName = this.NormaliseAssetName(assetName);
+
+            // load game content
+            if (!this.IsModFolder && !assetName.StartsWith(this.ModContentPrefix))
+                return this.LoadImpl<T>(assetName, language);
+
+            // load mod content
+            SContentLoadException GetContentError(string reasonPhrase) => new SContentLoadException($"Failed loading content asset '{assetName}': {reasonPhrase}");
+            try
+            {
+                // try cache
+                if (this.IsLoaded(assetName))
+                    return this.LoadImpl<T>(assetName, language);
+
+                // get file
+                FileInfo file = this.GetModFile(assetName);
+                if (!file.Exists)
+                    throw GetContentError("the specified path doesn't exist.");
+
+                // load content
+                switch (file.Extension.ToLower())
+                {
+                    // XNB file
+                    case ".xnb":
+                        return this.LoadImpl<T>(assetName, language);
+
+                    // unpacked map
+                    case ".tbin":
+                        throw GetContentError($"can't read unpacked map file '{assetName}' directly from the underlying content manager. It must be loaded through the mod's {typeof(IModHelper)}.{nameof(IModHelper.Content)} helper.");
+
+                    // unpacked image
+                    case ".png":
+                        // validate
+                        if (typeof(T) != typeof(Texture2D))
+                            throw GetContentError($"can't read file with extension '{file.Extension}' as type '{typeof(T)}'; must be type '{typeof(Texture2D)}'.");
+
+                        // fetch & cache
+                        using (FileStream stream = File.OpenRead(file.FullName))
+                        {
+                            Texture2D texture = Texture2D.FromStream(Game1.graphics.GraphicsDevice, stream);
+                            texture = this.PremultiplyTransparency(texture);
+                            this.Inject(assetName, texture);
+                            return (T)(object)texture;
+                        }
+
+                    default:
+                        throw GetContentError($"unknown file extension '{file.Extension}'; must be one of '.png', '.tbin', or '.xnb'.");
+                }
+            }
+            catch (Exception ex) when (!(ex is SContentLoadException))
+            {
+                if (ex.GetInnermostException() is DllNotFoundException dllEx && dllEx.Message == "libgdiplus.dylib")
+                    throw GetContentError("couldn't find libgdiplus, which is needed to load mod images. Make sure Mono is installed and you're running the game through the normal launcher.");
+                throw new SContentLoadException($"The content manager failed loading content asset '{assetName}'.", ex);
+            }
+        }
+
+        /// <summary>Load the base asset without localisation.</summary>
+        /// <typeparam name="T">The type of asset to load.</typeparam>
+        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
+        public override T LoadBase<T>(string assetName)
+        {
+            return this.Load<T>(assetName, LanguageCode.en);
+        }
+
+        /// <summary>Inject an asset into the cache.</summary>
+        /// <typeparam name="T">The type of asset to inject.</typeparam>
+        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
+        /// <param name="value">The asset value.</param>
+        public void Inject<T>(string assetName, T value)
+        {
+            assetName = this.NormaliseAssetName(assetName);
+            this.Cache[assetName] = value;
+        }
+
+        /// <summary>Create a new content manager for temporary use.</summary>
+        public override LocalizedContentManager CreateTemporary()
+        {
+            return this.Coordinator.CreateContentManager("(temporary)", isModFolder: false);
+        }
+
+        /// <summary>Normalise path separators in a file path. For asset keys, see <see cref="NormaliseAssetName"/> instead.</summary>
+        /// <param name="path">The file path to normalise.</param>
+        [Pure]
+        public string NormalisePathSeparators(string path)
+        {
+            return this.Cache.NormalisePathSeparators(path);
+        }
+
+        /// <summary>Normalise an asset name so it's consistent with the underlying cache.</summary>
+        /// <param name="assetName">The asset key.</param>
+        [Pure]
+        public string NormaliseAssetName(string assetName)
+        {
+            return this.Cache.NormaliseKey(assetName);
+        }
+
+        /// <summary>Assert that the given key has a valid format.</summary>
+        /// <param name="key">The asset key to check.</param>
+        /// <exception cref="ArgumentException">The asset key is empty or contains invalid characters.</exception>
+        [SuppressMessage("ReSharper", "ParameterOnlyUsedForPreconditionCheck.Local", Justification = "Parameter is only used for assertion checks by design.")]
+        public void AssertValidAssetKeyFormat(string key)
+        {
+            if (string.IsNullOrWhiteSpace(key))
+                throw new ArgumentException("The asset key or local path is empty.");
+            if (key.Intersect(Path.GetInvalidPathChars()).Any())
+                throw new ArgumentException("The asset key or local path contains invalid characters.");
+        }
+
+        /// <summary>Convert an absolute file path into an appropriate asset name.</summary>
+        /// <param name="absolutePath">The absolute path to the file.</param>
+        /// <param name="relativeTo">The folder to which to get a relative path.</param>
+        public string GetAssetNameFromFilePath(string absolutePath, ContentSource relativeTo)
+        {
+#if SMAPI_FOR_WINDOWS
+            // XNA doesn't allow absolute asset paths, so get a path relative to the source folder
+            string sourcePath = relativeTo == ContentSource.GameContent ? this.Coordinator.FullRootDirectory : this.FullRootDirectory;
+            return this.GetRelativePath(sourcePath, absolutePath);
+#else
+            // MonoGame is weird about relative paths on Mac, but allows absolute paths
+            return absolutePath;
+#endif
+        }
+
+        /****
+        ** Content loading
+        ****/
+        /// <summary>Get the current content locale.</summary>
+        public string GetLocale()
+        {
+            return this.GetLocale(this.GetCurrentLanguage());
+        }
+
+        /// <summary>The locale for a language.</summary>
+        /// <param name="language">The language.</param>
+        public string GetLocale(LocalizedContentManager.LanguageCode language)
+        {
+            return this.LanguageCodeString(language);
+        }
+
+        /// <summary>Get whether the content manager has already loaded and cached the given asset.</summary>
+        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
+        public bool IsLoaded(string assetName)
+        {
+            assetName = this.Cache.NormaliseKey(assetName);
+            return this.IsNormalisedKeyLoaded(assetName);
+        }
+
+        /// <summary>Get the cached asset keys.</summary>
+        public IEnumerable<string> GetAssetKeys()
+        {
+            return this.Cache.Keys
+                .Select(this.GetAssetName)
+                .Distinct();
+        }
+
+        /****
+        ** Cache invalidation
+        ****/
+        /// <summary>Purge matched assets from the cache.</summary>
+        /// <param name="predicate">Matches the asset keys to invalidate.</param>
+        /// <param name="dispose">Whether to dispose invalidated assets. This should only be <c>true</c> when they're being invalidated as part of a dispose, to avoid crashing the game.</param>
+        /// <returns>Returns the number of invalidated assets.</returns>
+        public IEnumerable<string> InvalidateCache(Func<string, Type, bool> predicate, bool dispose = false)
+        {
+            HashSet<string> removeAssetNames = new HashSet<string>(StringComparer.InvariantCultureIgnoreCase);
+            this.Cache.Remove((key, type) =>
+            {
+                this.ParseCacheKey(key, out string assetName, out _);
+                if (removeAssetNames.Contains(assetName) || predicate(assetName, type))
+                {
+                    removeAssetNames.Add(assetName);
+                    return true;
+                }
+                return false;
+            });
+
+            return removeAssetNames;
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /****
+        ** Asset name/key handling
+        ****/
+        /// <summary>Get a directory or file path relative to the content root.</summary>
+        /// <param name="sourcePath">The source file path.</param>
+        /// <param name="targetPath">The target file path.</param>
+        private string GetRelativePath(string sourcePath, string targetPath)
+        {
+            return PathUtilities.GetRelativePath(sourcePath, targetPath);
+        }
+
+        /// <summary>Get the locale codes (like <c>ja-JP</c>) used in asset keys.</summary>
+        private IDictionary<LocalizedContentManager.LanguageCode, string> GetKeyLocales()
+        {
+            // create locale => code map
+            IDictionary<LocalizedContentManager.LanguageCode, string> map = new Dictionary<LocalizedContentManager.LanguageCode, string>();
+            foreach (LocalizedContentManager.LanguageCode code in Enum.GetValues(typeof(LocalizedContentManager.LanguageCode)))
+                map[code] = this.GetLocale(code);
+
+            return map;
+        }
+
+        /// <summary>Get the asset name from a cache key.</summary>
+        /// <param name="cacheKey">The input cache key.</param>
+        private string GetAssetName(string cacheKey)
+        {
+            this.ParseCacheKey(cacheKey, out string assetName, out string _);
+            return assetName;
+        }
+
+        /// <summary>Parse a cache key into its component parts.</summary>
+        /// <param name="cacheKey">The input cache key.</param>
+        /// <param name="assetName">The original asset name.</param>
+        /// <param name="localeCode">The asset locale code (or <c>null</c> if not localised).</param>
+        private void ParseCacheKey(string cacheKey, out string assetName, out string localeCode)
+        {
+            // handle localised key
+            if (!string.IsNullOrWhiteSpace(cacheKey))
+            {
+                int lastSepIndex = cacheKey.LastIndexOf(".", StringComparison.InvariantCulture);
+                if (lastSepIndex >= 0)
+                {
+                    string suffix = cacheKey.Substring(lastSepIndex + 1, cacheKey.Length - lastSepIndex - 1);
+                    if (this.LanguageCodes.ContainsKey(suffix))
+                    {
+                        assetName = cacheKey.Substring(0, lastSepIndex);
+                        localeCode = cacheKey.Substring(lastSepIndex + 1, cacheKey.Length - lastSepIndex - 1);
+                        return;
+                    }
+                }
+            }
+
+            // handle simple key
+            assetName = cacheKey;
+            localeCode = null;
+        }
+
+        /****
+        ** Cache handling
+        ****/
+        /// <summary>Get whether an asset has already been loaded.</summary>
+        /// <param name="normalisedAssetName">The normalised asset name.</param>
+        private bool IsNormalisedKeyLoaded(string normalisedAssetName)
+        {
+            // default English
+            if (this.Language == LocalizedContentManager.LanguageCode.en)
+                return this.Cache.ContainsKey(normalisedAssetName);
+
+            // translated
+            if (!this.IsLocalisableLookup.TryGetValue(normalisedAssetName, out bool localisable))
+                return false;
+            return localisable
+                ? this.Cache.ContainsKey($"{normalisedAssetName}.{this.GetLocale(this.GetCurrentLanguage())}")
+                : this.Cache.ContainsKey(normalisedAssetName);
+        }
+
+        /****
+        ** Content loading
+        ****/
+        /// <summary>Load an asset name without heuristics to support mod content.</summary>
+        /// <typeparam name="T">The type of asset to load.</typeparam>
+        /// <param name="assetName">The asset path relative to the loader root directory, not including the <c>.xnb</c> extension.</param>
+        /// <param name="language">The language code for which to load content.</param>
+        private T LoadImpl<T>(string assetName, LocalizedContentManager.LanguageCode language)
+        {
+            // skip if already loaded
+            if (this.IsNormalisedKeyLoaded(assetName))
+                return base.Load<T>(assetName, language);
+
+            // load asset
+            T data;
+            if (this.AssetsBeingLoaded.Contains(assetName))
+            {
+                this.Monitor.Log($"Broke loop while loading asset '{assetName}'.", LogLevel.Warn);
+                this.Monitor.Log($"Bypassing mod loaders for this asset. Stack trace:\n{Environment.StackTrace}", LogLevel.Trace);
+                data = base.Load<T>(assetName, language);
+            }
+            else
+            {
+                data = this.AssetsBeingLoaded.Track(assetName, () =>
+                {
+                    string locale = this.GetLocale(language);
+                    IAssetInfo info = new AssetInfo(locale, assetName, typeof(T), this.NormaliseAssetName);
+                    IAssetData asset =
+                        this.ApplyLoader<T>(info)
+                        ?? new AssetDataForObject(info, base.Load<T>(assetName, language), this.NormaliseAssetName);
+                    asset = this.ApplyEditors<T>(info, asset);
+                    return (T)asset.Data;
+                });
+            }
+
+            // update cache & return data
+            this.Inject(assetName, data);
+            return data;
+        }
+
+        /// <summary>Get a file from the mod folder.</summary>
+        /// <param name="path">The asset path relative to the content folder.</param>
+        private FileInfo GetModFile(string path)
+        {
+            // try exact match
+            FileInfo file = new FileInfo(Path.Combine(this.FullRootDirectory, path));
+
+            // try with default extension
+            if (!file.Exists && file.Extension.ToLower() != ".xnb")
+            {
+                FileInfo result = new FileInfo(file.FullName + ".xnb");
+                if (result.Exists)
+                    file = result;
+            }
+
+            return file;
+        }
+
+        /// <summary>Load the initial asset from the registered <see cref="Loaders"/>.</summary>
+        /// <param name="info">The basic asset metadata.</param>
+        /// <returns>Returns the loaded asset metadata, or <c>null</c> if no loader matched.</returns>
+        private IAssetData ApplyLoader<T>(IAssetInfo info)
+        {
+            // find matching loaders
+            var loaders = this.GetInterceptors(this.Loaders)
+                .Where(entry =>
+                {
+                    try
+                    {
+                        return entry.Value.CanLoad<T>(info);
+                    }
+                    catch (Exception ex)
+                    {
+                        entry.Key.LogAsMod($"Mod failed when checking whether it could load asset '{info.AssetName}', and will be ignored. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
+                        return false;
+                    }
+                })
+                .ToArray();
+
+            // validate loaders
+            if (!loaders.Any())
+                return null;
+            if (loaders.Length > 1)
+            {
+                string[] loaderNames = loaders.Select(p => p.Key.DisplayName).ToArray();
+                this.Monitor.Log($"Multiple mods want to provide the '{info.AssetName}' asset ({string.Join(", ", loaderNames)}), but an asset can't be loaded multiple times. SMAPI will use the default asset instead; uninstall one of the mods to fix this. (Message for modders: you should usually use {typeof(IAssetEditor)} instead to avoid conflicts.)", LogLevel.Warn);
+                return null;
+            }
+
+            // fetch asset from loader
+            IModMetadata mod = loaders[0].Key;
+            IAssetLoader loader = loaders[0].Value;
+            T data;
+            try
+            {
+                data = loader.Load<T>(info);
+                this.Monitor.Log($"{mod.DisplayName} loaded asset '{info.AssetName}'.", LogLevel.Trace);
+            }
+            catch (Exception ex)
+            {
+                mod.LogAsMod($"Mod crashed when loading asset '{info.AssetName}'. SMAPI will use the default asset instead. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
+                return null;
+            }
+
+            // validate asset
+            if (data == null)
+            {
+                mod.LogAsMod($"Mod incorrectly set asset '{info.AssetName}' to a null value; ignoring override.", LogLevel.Error);
+                return null;
+            }
+
+            // return matched asset
+            return new AssetDataForObject(info, data, this.NormaliseAssetName);
+        }
+
+        /// <summary>Apply any <see cref="Editors"/> to a loaded asset.</summary>
+        /// <typeparam name="T">The asset type.</typeparam>
+        /// <param name="info">The basic asset metadata.</param>
+        /// <param name="asset">The loaded asset.</param>
+        private IAssetData ApplyEditors<T>(IAssetInfo info, IAssetData asset)
+        {
+            IAssetData GetNewData(object data) => new AssetDataForObject(info, data, this.NormaliseAssetName);
+
+            // edit asset
+            foreach (var entry in this.GetInterceptors(this.Editors))
+            {
+                // check for match
+                IModMetadata mod = entry.Key;
+                IAssetEditor editor = entry.Value;
+                try
+                {
+                    if (!editor.CanEdit<T>(info))
+                        continue;
+                }
+                catch (Exception ex)
+                {
+                    mod.LogAsMod($"Mod crashed when checking whether it could edit asset '{info.AssetName}', and will be ignored. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
+                    continue;
+                }
+
+                // try edit
+                object prevAsset = asset.Data;
+                try
+                {
+                    editor.Edit<T>(asset);
+                    this.Monitor.Log($"{mod.DisplayName} intercepted {info.AssetName}.", LogLevel.Trace);
+                }
+                catch (Exception ex)
+                {
+                    mod.LogAsMod($"Mod crashed when editing asset '{info.AssetName}', which may cause errors in-game. Error details:\n{ex.GetLogSummary()}", LogLevel.Error);
+                }
+
+                // validate edit
+                if (asset.Data == null)
+                {
+                    mod.LogAsMod($"Mod incorrectly set asset '{info.AssetName}' to a null value; ignoring override.", LogLevel.Warn);
+                    asset = GetNewData(prevAsset);
+                }
+                else if (!(asset.Data is T))
+                {
+                    mod.LogAsMod($"Mod incorrectly set asset '{asset.AssetName}' to incompatible type '{asset.Data.GetType()}', expected '{typeof(T)}'; ignoring override.", LogLevel.Warn);
+                    asset = GetNewData(prevAsset);
+                }
+            }
+
+            // return result
+            return asset;
+        }
+
+        /// <summary>Get all registered interceptors from a list.</summary>
+        private IEnumerable<KeyValuePair<IModMetadata, T>> GetInterceptors<T>(IDictionary<IModMetadata, IList<T>> entries)
+        {
+            foreach (var entry in entries)
+            {
+                IModMetadata mod = entry.Key;
+                IList<T> interceptors = entry.Value;
+
+                // registered editors
+                foreach (T interceptor in interceptors)
+                    yield return new KeyValuePair<IModMetadata, T>(mod, interceptor);
+            }
+        }
+
+        /// <summary>Premultiply a texture's alpha values to avoid transparency issues in the game. This is only possible if the game isn't currently drawing.</summary>
+        /// <param name="texture">The texture to premultiply.</param>
+        /// <returns>Returns a premultiplied texture.</returns>
+        /// <remarks>Based on <a href="https://gist.github.com/Layoric/6255384">code by Layoric</a>.</remarks>
+        private Texture2D PremultiplyTransparency(Texture2D texture)
+        {
+            // validate
+            if (Context.IsInDrawLoop)
+                throw new NotSupportedException("Can't load a PNG file while the game is drawing to the screen. Make sure you load content outside the draw loop.");
+
+            // process texture
+            SpriteBatch spriteBatch = Game1.spriteBatch;
+            GraphicsDevice gpu = Game1.graphics.GraphicsDevice;
+            using (RenderTarget2D renderTarget = new RenderTarget2D(Game1.graphics.GraphicsDevice, texture.Width, texture.Height))
+            {
+                // create blank render target to premultiply
+                gpu.SetRenderTarget(renderTarget);
+                gpu.Clear(Color.Black);
+
+                // multiply each color by the source alpha, and write just the color values into the final texture
+                spriteBatch.Begin(SpriteSortMode.Immediate, new BlendState
+                {
+                    ColorDestinationBlend = Blend.Zero,
+                    ColorWriteChannels = ColorWriteChannels.Red | ColorWriteChannels.Green | ColorWriteChannels.Blue,
+                    AlphaDestinationBlend = Blend.Zero,
+                    AlphaSourceBlend = Blend.SourceAlpha,
+                    ColorSourceBlend = Blend.SourceAlpha
+                });
+                spriteBatch.Draw(texture, texture.Bounds, Color.White);
+                spriteBatch.End();
+
+                // copy the alpha values from the source texture into the final one without multiplying them
+                spriteBatch.Begin(SpriteSortMode.Immediate, new BlendState
+                {
+                    ColorWriteChannels = ColorWriteChannels.Alpha,
+                    AlphaDestinationBlend = Blend.Zero,
+                    ColorDestinationBlend = Blend.Zero,
+                    AlphaSourceBlend = Blend.One,
+                    ColorSourceBlend = Blend.One
+                });
+                spriteBatch.Draw(texture, texture.Bounds, Color.White);
+                spriteBatch.End();
+
+                // release GPU
+                gpu.SetRenderTarget(null);
+
+                // extract premultiplied data
+                Color[] data = new Color[texture.Width * texture.Height];
+                renderTarget.GetData(data);
+
+                // unset texture from GPU to regain control
+                gpu.Textures[0] = null;
+
+                // update texture with premultiplied data
+                texture.SetData(data);
+            }
+
+            return texture;
+        }
+    }
+}