Conditional state restore and BufferUploader sanity check

- Only restore state that has changed
 - Sanity check to fix error condition on reset

src/main/java/com/jozufozu/flywheel/backend/gl/GlStateTracker.java

@@ -45,11 +45,18 @@ public class GlStateTracker {
 			GlBufferType[] values = GlBufferType.values();
 
 			for (int i = 0; i < values.length; i++) {
+				if (buffers[i] != GlStateTracker.buffers[i]) {
 					GlStateManager._glBindBuffer(values[i].glEnum, buffers[i]);
 				}
+			}
 
+			if (vao != GlStateTracker.vao) {
 				GlStateManager._glBindVertexArray(vao);
+			}
+
+			if (program != GlStateTracker.program) {
 				GlStateManager._glUseProgram(program);
 			}
 		}
 	}
+}

src/main/java/com/jozufozu/flywheel/mixin/BufferUploaderMixin.java

@@ -0,0 +1,29 @@
+package com.jozufozu.flywheel.mixin;
+
+import javax.annotation.Nullable;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import com.jozufozu.flywheel.backend.gl.GlStateTracker;
+import com.mojang.blaze3d.vertex.BufferUploader;
+import com.mojang.blaze3d.vertex.VertexFormat;
+
+@Mixin(BufferUploader.class)
+public class BufferUploaderMixin {
+
+	@Shadow
+	@Nullable
+	private static VertexFormat lastFormat;
+
+	@Inject(method = "reset", at = @At("HEAD"))
+	private static void stopBufferUploaderFromClearingBufferStateIfNothingIsBound(CallbackInfo ci) {
+		// Trust our tracker over BufferUploader's.
+		if (GlStateTracker.getVertexArray() == 0) {
+			lastFormat = null;
+		}
+	}
+}

src/main/resources/flywheel.mixins.json

@@ -7,6 +7,7 @@
   "client": [
     "BlockEntityTypeMixin",
     "BufferBuilderMixin",
+    "BufferUploaderMixin",
     "CameraMixin",
     "CancelEntityRenderMixin",
     "ChunkRebuildHooksMixin",