Automatically disable and re-enable Optifine's Fast Render setting before rendering a video

src/main/java/com/replaymod/compat/ReplayModCompat.java

@@ -1,5 +1,6 @@
 package com.replaymod.compat;
 
+import com.replaymod.compat.optifine.DisableFastRender;
 import com.replaymod.compat.shaders.ShaderBeginRender;
 import com.replaymod.core.ReplayMod;
 import net.minecraftforge.fml.common.FMLCommonHandler;
@@ -18,6 +19,7 @@ public class ReplayModCompat {
     public void init(FMLInitializationEvent event) {
         EventBus bus = FMLCommonHandler.instance().bus();
         bus.register(new ShaderBeginRender());
+        bus.register(new DisableFastRender());
     }
 
 }

src/main/java/com/replaymod/compat/optifine/DisableFastRender.java

@@ -0,0 +1,37 @@
+package com.replaymod.compat.optifine;
+
+import com.replaymod.render.events.ReplayRenderEvent;
+import net.minecraft.client.Minecraft;
+import net.minecraftforge.fml.client.FMLClientHandler;
+import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
+
+public class DisableFastRender {
+
+    private final Minecraft mc = Minecraft.getMinecraft();
+
+    private boolean wasFastRender = false;
+
+    @SubscribeEvent
+    public void onRenderBegin(ReplayRenderEvent.Pre event) {
+        if (!FMLClientHandler.instance().hasOptifine()) return;
+
+        try {
+            wasFastRender = (boolean) OptifineReflection.gameSettings_ofFastRender.get(mc.gameSettings);
+            OptifineReflection.gameSettings_ofFastRender.set(mc.gameSettings, false);
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+    }
+
+    @SubscribeEvent
+    public void onRenderEnd(ReplayRenderEvent.Post event){
+        if (!FMLClientHandler.instance().hasOptifine()) return;
+
+        try {
+            OptifineReflection.gameSettings_ofFastRender.set(mc.gameSettings, wasFastRender);
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+    }
+
+}

src/main/java/com/replaymod/compat/optifine/OptifineReflection.java

@@ -0,0 +1,27 @@
+package com.replaymod.compat.optifine;
+
+import net.minecraft.client.settings.GameSettings;
+
+import java.lang.reflect.Field;
+
+public class OptifineReflection {
+
+    // GameSettings.ofFastRender
+    public static Field gameSettings_ofFastRender;
+
+    static {
+        try {
+            // this throws an ignored ClassNotFoundException if Optifine isn't installed
+            Class.forName("Config");
+
+            gameSettings_ofFastRender = GameSettings.class.getDeclaredField("ofFastRender");
+            gameSettings_ofFastRender.setAccessible(true);
+        } catch (ClassNotFoundException ignore) {
+            // no optifine installed
+        } catch (NoSuchFieldException e) {
+            // the field wasn't found. Has it been renamed?
+            e.printStackTrace();
+        }
+    }
+
+}