detect libgdiplus-missing exception and show a friendly error instead (#408)

3 files changed, 13 insertions, 1 deletions

diff --git a/docs/release-notes.md b/docs/release-notes.md
index fa04c055..a76b5e19 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -5,6 +5,7 @@
   * Fixed `GraphicsEvents.OnPostRenderEvent` not being raised in some specialised cases.
   * Fixed error when using the reflection API accesses with a property with either `get` and `set` missing.
   * Fixed issue where a mod could change the cursor position reported to other mods.
+  * Improved cryptic libgdiplus errors on Mac when Mono isn't installed.
 
 ## 2.2
 * For players:
diff --git a/src/SMAPI/Framework/InternalExtensions.cs b/src/SMAPI/Framework/InternalExtensions.cs
index f81e05a9..bec6c183 100644
--- a/src/SMAPI/Framework/InternalExtensions.cs
+++ b/src/SMAPI/Framework/InternalExtensions.cs
@@ -108,6 +108,15 @@ namespace StardewModdingAPI.Framework
             }
         }
 
+        /// <summary>Get the lowest exception in an exception stack.</summary>
+        /// <param name="exception">The exception from which to search.</param>
+        public static Exception GetInnermostException(this Exception exception)
+        {
+            while (exception.InnerException != null)
+                exception = exception.InnerException;
+            return exception;
+        }
+
         /****
         ** Sprite batch
         ****/
diff --git a/src/SMAPI/Framework/SContentManager.cs b/src/SMAPI/Framework/SContentManager.cs
index 1803098d..ebea6c84 100644
--- a/src/SMAPI/Framework/SContentManager.cs
+++ b/src/SMAPI/Framework/SContentManager.cs
@@ -205,7 +205,7 @@ namespace StardewModdingAPI.Framework
                 return this.LoadImpl<T>(assetName, instance);
 
             // load mod content
-            SContentLoadException GetContentError(string reasonPhrase) => new SContentLoadException($"Failed loading content asset '{assetName}': {reasonPhrase}.");
+            SContentLoadException GetContentError(string reasonPhrase) => new SContentLoadException($"Failed loading content asset '{assetName}': {reasonPhrase}");
             try
             {
                 return this.WithWriteLock(() =>
@@ -252,6 +252,8 @@ namespace StardewModdingAPI.Framework
             }
             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);
             }
         }