Potential rendering improvements (mostly stuff discovered while porting to 1.8 that didn't seem to have an effect in 1.7, but can't hurt to clean up).

src/main/scala/li/cil/oc/client/gui/Assembler.scala

@@ -101,12 +101,12 @@ class Assembler(playerInventory: InventoryPlayer, val assembler: tileentity.Asse
 
   override def drawGuiContainerBackgroundLayer(dt: Float, mouseX: Int, mouseY: Int) {
     GL11.glColor3f(1, 1, 1) // Required under Linux.
-    super.drawGuiContainerBackgroundLayer(dt, mouseX, mouseY)
     mc.renderEngine.bindTexture(Textures.guiRobotAssembler)
     drawTexturedModalRect(guiLeft, guiTop, 0, 0, xSize, ySize)
     if (assemblerContainer.isAssembling) progress.level = assemblerContainer.assemblyProgress / 100.0
     else progress.level = 0
     drawWidgets()
+    drawInventorySlots()
   }
 
   override protected def drawDisabledSlot(slot: ComponentSlot) {}

src/main/scala/li/cil/oc/client/gui/Disassembler.scala

@@ -21,7 +21,6 @@ class Disassembler(playerInventory: InventoryPlayer, val disassembler: tileentit
 
   override def drawGuiContainerBackgroundLayer(dt: Float, mouseX: Int, mouseY: Int) {
     GL11.glColor3f(1, 1, 1) // Required under Linux.
-    super.drawGuiContainerBackgroundLayer(dt, mouseX, mouseY)
     mc.renderEngine.bindTexture(Textures.guiDisassembler)
     drawTexturedModalRect(guiLeft, guiTop, 0, 0, xSize, ySize)
     progress.level = disassemblerContainer.disassemblyProgress / 100.0

src/main/scala/li/cil/oc/client/gui/Drone.scala

@@ -17,7 +17,6 @@ import net.minecraft.client.Minecraft
 import net.minecraft.client.gui.GuiButton
 import net.minecraft.client.renderer.Tessellator
 import net.minecraft.entity.player.InventoryPlayer
-import net.minecraft.inventory.Slot
 import org.lwjgl.opengl.GL11
 
 class Drone(playerInventory: InventoryPlayer, val drone: entity.Drone) extends DynamicGuiContainer(new container.Drone(playerInventory, drone)) with traits.DisplayBuffer {
@@ -117,14 +116,7 @@ class Drone(playerInventory: InventoryPlayer, val drone: entity.Drone) extends D
       drawSelection()
     }
 
-    GL11.glPushMatrix()
+    drawInventorySlots()
-    GL11.glTranslatef(guiLeft, guiTop, 0)
-    for (slot <- 0 until inventorySlots.inventorySlots.size()) {
-      drawSlotInventory(inventorySlots.inventorySlots.get(slot).asInstanceOf[Slot])
-    }
-    GL11.glPopMatrix()
-
-    RenderState.makeItBlend()
   }
 
   protected override def drawGradientRect(par1: Int, par2: Int, par3: Int, par4: Int, par5: Int, par6: Int) {

src/main/scala/li/cil/oc/client/gui/DynamicGuiContainer.scala

@@ -55,12 +55,17 @@ abstract class DynamicGuiContainer(container: Container) extends CustomGuiContai
     RenderState.makeItBlend()
     GL11.glDisable(GL11.GL_LIGHTING)
 
+    drawInventorySlots()
+  }
+
+  protected def drawInventorySlots(): Unit = {
     GL11.glPushMatrix()
     GL11.glTranslatef(guiLeft, guiTop, 0)
     for (slot <- 0 until inventorySlots.inventorySlots.size()) {
       drawSlotInventory(inventorySlots.inventorySlots.get(slot).asInstanceOf[Slot])
     }
     GL11.glPopMatrix()
+    RenderState.makeItBlend()
   }
 
   override def drawScreen(mouseX: Int, mouseY: Int, dt: Float) {

src/main/scala/li/cil/oc/client/gui/Raid.scala

@@ -21,7 +21,6 @@ class Raid(playerInventory: InventoryPlayer, val raid: tileentity.Raid) extends
 
   override def drawGuiContainerBackgroundLayer(dt: Float, mouseX: Int, mouseY: Int) {
     GL11.glColor3f(1, 1, 1) // Required under Linux.
-    super.drawGuiContainerBackgroundLayer(dt, mouseX, mouseY)
     mc.renderEngine.bindTexture(Textures.guiRaid)
     drawTexturedModalRect(guiLeft, guiTop, 0, 0, xSize, ySize)
   }

src/main/scala/li/cil/oc/client/gui/Robot.scala

@@ -18,7 +18,6 @@ import net.minecraft.client.Minecraft
 import net.minecraft.client.gui.GuiButton
 import net.minecraft.client.renderer.Tessellator
 import net.minecraft.entity.player.InventoryPlayer
-import net.minecraft.inventory.Slot
 import org.lwjgl.input.Keyboard
 import org.lwjgl.input.Mouse
 import org.lwjgl.opengl.GL11
@@ -159,14 +158,7 @@ class Robot(playerInventory: InventoryPlayer, val robot: tileentity.Robot) exten
       drawSelection()
     }
 
-    GL11.glPushMatrix()
+    drawInventorySlots()
-    GL11.glTranslatef(guiLeft, guiTop, 0)
-    for (slot <- 0 until inventorySlots.inventorySlots.size()) {
-      drawSlotInventory(inventorySlots.inventorySlots.get(slot).asInstanceOf[Slot])
-    }
-    GL11.glPopMatrix()
-
-    RenderState.makeItBlend()
   }
 
   protected override def drawGradientRect(par1: Int, par2: Int, par3: Int, par4: Int, par5: Int, par6: Int) {