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();
+        }
+    }
+
+}

src/main/java/com/replaymod/render/events/ReplayRenderEvent.java

@@ -0,0 +1,24 @@
+package com.replaymod.render.events;
+
+import com.replaymod.render.rendering.VideoRenderer;
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+import net.minecraftforge.fml.common.eventhandler.Event;
+
+@RequiredArgsConstructor
+public abstract class ReplayRenderEvent extends Event {
+    @Getter
+    private final VideoRenderer videoRenderer;
+
+    public static class Pre extends ReplayRenderEvent {
+        public Pre(VideoRenderer videoRenderer) {
+            super(videoRenderer);
+        }
+    }
+
+    public static class Post extends ReplayRenderEvent {
+        public Post(VideoRenderer videoRenderer) {
+            super(videoRenderer);
+        }
+    }
+}

src/main/java/com/replaymod/render/rendering/VideoRenderer.java

@@ -7,6 +7,7 @@ import com.replaymod.render.RenderSettings;
 import com.replaymod.render.ReplayModRender;
 import com.replaymod.render.VideoWriter;
 import com.replaymod.render.capturer.RenderInfo;
+import com.replaymod.render.events.ReplayRenderEvent;
 import com.replaymod.render.frame.RGBFrame;
 import com.replaymod.render.gui.GuiRenderingDone;
 import com.replaymod.render.gui.GuiVideoRenderer;
@@ -22,6 +23,7 @@ import net.minecraft.client.gui.ScaledResolution;
 import net.minecraft.client.renderer.OpenGlHelper;
 import net.minecraft.client.shader.Framebuffer;
 import net.minecraft.util.Timer;
+import net.minecraftforge.fml.common.FMLCommonHandler;
 import org.lwjgl.input.Mouse;
 import org.lwjgl.opengl.Display;
 import org.lwjgl.util.Dimension;
@@ -86,6 +88,8 @@ public class VideoRenderer implements RenderInfo {
      * @return {@code true} if rendering was successful, {@code false} if the user aborted rendering (or the window was closed)
      */
     public boolean renderVideo() {
+        FMLCommonHandler.instance().bus().post(new ReplayRenderEvent.Pre(this));
+
         setup();
 
         // Because this might take some time to prepare we'll render the GUI at least once to not confuse the user
@@ -129,6 +133,9 @@ public class VideoRenderer implements RenderInfo {
         }
 
         finish();
+
+        FMLCommonHandler.instance().bus().post(new ReplayRenderEvent.Post(this));
+
         return !cancelled;
     }