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[1.14.4] Modifying the containers & screens of vanilla entities


Choco
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I'm mostly new to modding with Forge (at least this time I'm trying to take it more seriously) and for the most part I've been able to do some research and come up with answers for questions as they arise. However I've been stumped trying to figure out how to modify the inventory of an existing vanilla entity. The goal is to add a third inventory slot to the horse inventory though I'm unsure how to proceed. At the moment I've handled the capabilities just fine and they're registered on the horse but that doesn't get me all too far in that there's no slot to interact with in order to modify that capability.

 

I've looked into mods that manipulate the player inventory to add slots (Baubles notably) though because the mod was last updated for Forge 1.11, the source isn't all too useful to me. Not to mention that modifying a player inventory is slightly different than a horse inventory as far as I can tell. My thoughts on how to tackle this issue thus far have been to

  • Listen for the GuiOpenEvent and
    • ... set the GUI to one of mine own that extends HorseInventoryScreen (and consequently pass one that extends HorseInventoryContainer) - though this sounds like mod incompatibility hell
    • ... manipulate the existing GUI using reflection to access the container and add a slot. This is client-sided only so the server would not like me very much

 

Neither of the above seem to solve my issue although I've not attempted the first in fear that my mod will not remain compatible with other mods. Is there a more fluid or a proper way of actually achieving this? I'm working with Forge 28.1.96 as of writing this thread though I do need to update, or even just revert to a stable build. Any guidance would be much appreciated.

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You need to:

  1. Subscribe to PlayerContainerEvent.Open, check if it's the Container you are looking for and if so, add your slot using Container#addSlot (you'll need reflection).
  2. Subscribe to GuiOpenEvent, check if it's the screen you are looking for and if so, add your slot here as well (ContainerScreen#getContainer and then Container#addSlot).
    You will need to ensure that your Slot is placed at the same position in the list, because otherwise the server<>client sync won't work. This isn't trivial, because other mods might be doing the same procedure and the event handlers might run in different order.
  3. Subscribe to GuiContainerEvent.DrawBackground to draw the background for your slot over the normal container GUI.
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28 minutes ago, diesieben07 said:

You need to:

  1. Subscribe to PlayerContainerEvent.Open, check if it's the Container you are looking for and if so, add your slot using Container#addSlot (you'll need reflection).
  2. Subscribe to GuiOpenEvent, check if it's the screen you are looking for and if so, add your slot here as well (ContainerScreen#getContainer and then Container#addSlot).
    You will need to ensure that your Slot is placed at the same position in the list, because otherwise the server<>client sync won't work. This isn't trivial, because other mods might be doing the same procedure and the event handlers might run in different order.
  3. Subscribe to GuiContainerEvent.DrawBackground to draw the background for your slot over the normal container GUI.

Surprisingly enough, I was somewhat close. I had added the slot reflectively using GuiOpenEvent, though doing the same in PlayerContainerEvent.Open resolved the server-sided errors which is nice. A few follow-up questions:

  1. Am I correct in assuming that PlayerContainerEvent is server-sided and GuiOpenEvent is client-sided? This doesn't affect my code in any way, I'm more just inclined to learn more about what affects which distribution.
  2. Is there any good way to ensure the same slot position? As far as I'm aware, addSlot() is the only available option, I have no way of dictating at which position the slot should be added unless of course I reflectively access the inventory contents and set the index. Should this be something I should even concern myself with?
  3. Is there any proper documentation, information or tutorials on calls to AbstractGui#blit() (or really any of its rendering-related methods). I could probably find information in a quick Google search but I might as well ask here as well.
  4. Unrelated to modding: as a new member on the forums, how do I format in-line code in a reply :)

I appreciate the response. I can finally move forward with the mod again!

 

EDIT: Suppose that's what I get for speaking too soon. I continue to get an ArrayIndexOutOfBoundsException when attempting to interact with the slot. I suppose this is where my capabilities come in?

Edited by Choco
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21 minutes ago, Choco said:

Am I correct in assuming that PlayerContainerEvent is server-sided and GuiOpenEvent is client-sided?

Yes. Although distribution is the wrong word here. This is about logical sides (integrated server uses PlayerContainerEvent.Open).

 

22 minutes ago, Choco said:

Is there any good way to ensure the same slot position? As far as I'm aware, addSlot() is the only available option, I have no way of dictating at which position the slot should be added unless of course I reflectively access the inventory contents and set the index. Should this be something I should even concern myself with?

I am not sure how you would approach it. Ideally you'd have to somehow tell the client where to put the slot. If other mods modify the same container in the same way, this could lead to the server and client adding the slots in different order.

 

23 minutes ago, Choco said:

Is there any proper documentation, information or tutorials on calls to AbstractGui#blit() (or really any of its rendering-related methods). I could probably find information in a quick Google search but I might as well ask here as well.

Probably look at vanilla for examples.

 

23 minutes ago, Choco said:

Unrelated to modding: as a new member on the forums, how do I format in-line code in a reply

Use the tt button in the formatting toolbar.

 

24 minutes ago, Choco said:

Suppose that's what I get for speaking too soon. I continue to get an ArrayIndexOutOfBoundsException when attempting to interact with the slot. I suppose this is where my capabilities come in?

Post your code and the stacktrace.

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14 minutes ago, diesieben07 said:

Probably look at vanilla for examples.

Was confused at first but I got that figured out! For those that find this thread in the future, parameters are as follows:

blit(screenX, screenY, textureX, textureY, width, height)

 

14 minutes ago, diesieben07 said:

Post your code and the stacktrace.

Certainly. You'll have to excuse the non-cached reflection, I'm trying to at least have it work properly first

    private static final ResourceLocation HORSE_GUI_TEXTURES = new ResourceLocation("textures/gui/container/horse.png");
    private static final Function<IInventory, Slot> SLOT_CREATOR = i -> new Slot(i, 2, 8, 54);
    
    @SubscribeEvent
    public static void addSlotServerSide(PlayerContainerEvent.Open event) {
        Container container = event.getContainer();
        if (container instanceof HorseInventoryContainer) {
            addSlotToHorseContainer((HorseInventoryContainer) container, SLOT_CREATOR);
        }
    }
    
    @SubscribeEvent
    public static void addSlotClientSide(GuiOpenEvent event) {
        Screen screen = event.getGui();
        if (screen instanceof HorseInventoryScreen) {
            addSlotToHorseContainer(((HorseInventoryScreen) screen).getContainer(), SLOT_CREATOR);
        }
    }
    
    private static void addSlotToHorseContainer(HorseInventoryContainer container, Function<IInventory, Slot> slotCreator) {
        try {
            Field fieldHorseInventory = HorseInventoryContainer.class.getDeclaredField("horseInventory");
            IInventory horseInventory = (IInventory) ReflectionUtil.getFieldValue(fieldHorseInventory, container);

            addSlotReflectively(container, slotCreator.apply(horseInventory));
        } catch (ReflectiveOperationException e) {
            e.printStackTrace();
        }
    }
    
    private static void addSlotReflectively(Container container, Slot slot) {
        try {
            Method methodAddSlot = Container.class.getDeclaredMethod("addSlot", Slot.class);
            methodAddSlot.setAccessible(true);
            methodAddSlot.invoke(container, slot);
        } catch (ReflectiveOperationException e) {
            e.printStackTrace();
        }
    }
    
    // Some rendering code... this works fine, irrelevant to the slot adding, figured I'd include it anyways
    @SubscribeEvent
    public static void renderExtraSlot(GuiContainerEvent.DrawBackground event) {
        ContainerScreen<?> screen = event.getGuiContainer();
        if (screen instanceof HorseInventoryScreen) {
            GlStateManager.color4f(1.0F, 1.0F, 1.0F, 1.0F);
            Minecraft.getInstance().getTextureManager().bindTexture(HORSE_GUI_TEXTURES);
            
            int ySize = screen.getYSize();
            int i = (screen.width - screen.getXSize()) / 2;
            int j = (screen.height - ySize) / 2;

            // screen x, screen y, texture x, texture y, width, height
            screen.blit(i + 7, j + 53, 0, ySize, 18, 18);
        }
    }

 

Relevant stacktrace(s):

java.lang.ArrayIndexOutOfBoundsException: 2
	at java.util.Arrays$ArrayList.set(Arrays.java:3846) ~[?:1.8.0_221] {}
	at net.minecraft.util.NonNullList.set(NonNullList.java:50) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading}
	at net.minecraft.inventory.Inventory.setInventorySlotContents(Inventory.java:114) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading}
	at net.minecraft.inventory.container.Slot.putStack(Slot.java:84) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading}
	at net.minecraft.inventory.container.Container.slotClick(Container.java:273) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading}
	at net.minecraft.client.multiplayer.PlayerController.windowClick(PlayerController.java:397) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.inventory.ContainerScreen.handleMouseClick(ContainerScreen.java:534) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.inventory.ContainerScreen.mouseReleased(ContainerScreen.java:501) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.lambda$mouseButtonCallback$1(MouseHelper.java:93) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.Screen.wrapScreenError(Screen.java:441) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.mouseButtonCallback(MouseHelper.java:91) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36) ~[lwjgl-glfw-3.2.2.jar:build 10] {}
	at org.lwjgl.system.JNI.invokeV(Native Method) ~[lwjgl-3.2.2.jar:build 10] {}
	at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:3101) ~[lwjgl-glfw-3.2.2.jar:build 10] {}
	at net.minecraft.client.MainWindow.poll(MainWindow.java:403) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MainWindow.update(MainWindow.java:273) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.updateDisplay(Minecraft.java:982) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:946) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.run(Minecraft.java:384) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.main.Main.main(Main.java:128) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_221] {}
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_221] {}
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_221] {}
	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_221] {}
	at net.minecraftforge.userdev.FMLUserdevClientLaunchProvider.lambda$launchService$0(FMLUserdevClientLaunchProvider.java:55) ~[forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-4.1.0.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-4.1.0.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-4.1.0.jar:?] {}
	at cpw.mods.modlauncher.Launcher.run(Launcher.java:81) [modlauncher-4.1.0.jar:?] {}
	at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-4.1.0.jar:?] {}
	at net.minecraftforge.userdev.LaunchTesting.main(LaunchTesting.java:101) [forge-1.14.4-28.1.96_mapped_snapshot_20190719-1.14.3-recomp.jar:?] {}
-- Head --
Thread: Client thread
Stacktrace:
	at java.util.Arrays$ArrayList.set(Arrays.java:3846)
	at net.minecraft.util.NonNullList.set(NonNullList.java:50)
	at net.minecraft.inventory.Inventory.setInventorySlotContents(Inventory.java:114)
	at net.minecraft.inventory.container.Slot.putStack(Slot.java:84)
	at net.minecraft.inventory.container.Container.slotClick(Container.java:273)
	at net.minecraft.client.multiplayer.PlayerController.windowClick(PlayerController.java:397)
	at net.minecraft.client.gui.screen.inventory.ContainerScreen.handleMouseClick(ContainerScreen.java:534)
	at net.minecraft.client.gui.screen.inventory.ContainerScreen.mouseReleased(ContainerScreen.java:501)
	at net.minecraft.client.MouseHelper.lambda$mouseButtonCallback$1(MouseHelper.java:93)

-- Affected screen --
Details:
	Screen name: net.minecraft.client.gui.screen.inventory.HorseInventoryScreen
Stacktrace:
	at net.minecraft.client.gui.screen.Screen.wrapScreenError(Screen.java:441)
	at net.minecraft.client.MouseHelper.mouseButtonCallback(MouseHelper.java:91)
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36)
	at org.lwjgl.system.JNI.invokeV(Native Method)
	at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:3101)
	at net.minecraft.client.MainWindow.poll(MainWindow.java:403)
	at net.minecraft.client.MainWindow.update(MainWindow.java:273)

 

Worth noting that the listener class is annotated with @EventBusSubscriber(modid = MY_MOD_ID)

Edited by Choco
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9 minutes ago, diesieben07 said:

You are telling the slot to use index 2 of the horse inventory. The default horse inventory only has 2 slots, indices 0 and 1.

Correct, although that was my question to begin with. How am I meant to modify the inventory of an existing entity? I was under the impression that this would be addressed as well, though that mustn't be the case. The way you had described it in your initial reply had made it seem like the slots would have allowed the user to interact with them. Perhaps I misunderstood. I understand I am interacting with the 3rd slot (index 2) and I understand why I'm getting this exception, I'm just unsure how to address it. Overriding one of the existing slot indexes surely isn't an option. I want to maintain the vanilla functionality of a horse.

 

So to rephrase the question in the OP, what would be the correct approach to add a slot to a horse inventory with which a player may interact and place/take items?

Edited by Choco
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3 hours ago, Choco said:

At the moment I've handled the capabilities just fine and they're registered on the horse but that doesn't get me all too far in that there's no slot to interact with in order to modify that capability.

Since you said this, I assumed you had already done that...

You need a capability attached to horses, which stores an IItemHandler for your additional inventory space.

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9 minutes ago, diesieben07 said:

Since you said this, I assumed you had already done that...

You need a capability attached to horses, which stores an IItemHandler for your additional inventory space.

I do have an ItemStackHandler and it is attached :) It's actually attached in that same class (it was something I left out because it was irrelevant at the time).

    @SubscribeEvent
    public static void attachHorseCapabilities(AttachCapabilitiesEvent<Entity> event) {
        if (event.getObject() instanceof AbstractHorseEntity) {
            event.addCapability(new ResourceLocation(MOD_ID, "capability_mycustomslots"), new ThisIsntTheClassNameButYouGetTheIdea());
        }
    }

It's implemented correctly, supplies an additional slot index, serializes and deserializes to/from NBT, sure. Here's my confusion. How am I supposed to say "Hey, when you interact with this slot, you should be modifying this capability" because adding a slot reflectively to the horse container modifies what I assume is the horse inventory, correct? Should I be passing that capability somewhere so my slot knows to interact with that capability instead of the default, vanilla inventoryContents supplied by the inventory? I see only the IInventory passed to the Slot but as far as I'm concerned, that should be the horse inventory.

Edited by Choco
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1 minute ago, Choco said:

Here's my confusion. How am I supposed to say "Hey, when you interact with this slot, you should be modifying this capability"

If only the Slot constructor had a way to tell it which inventory to use... Oh, it does. It has an IInventory parameter. Use SlotItemHandler for the IItemHandler variant.

 

2 minutes ago, Choco said:

because adding a slot reflectively to the horse container modifies what I assume is the horse inventory, correct?

Incorrect. The slot modifies whatever inventory you give it.

 

3 minutes ago, Choco said:

Should I be passing that capability somewhere so my slot knows to interact with that capability instead of the default, vanilla inventorySlots supplied by the horse inventory?

Yes.

 

3 minutes ago, Choco said:

I see only the IInventory passed to the Slot but as far as I'm concerned, that should be the horse inventory.

If it's the horse inventory, then how is the slot supposed to know that it should look anywhere else?

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17 minutes ago, diesieben07 said:

If only the Slot constructor had a way to tell it which inventory to use... Oh, it does. It has an IInventory parameter. Use SlotItemHandler for the IItemHandler variant.

That was where my confusion layed. There was no mention of SlotItemHandler anywhere whatsoever on the capabilities page, or really anywhere I did prior research before creating this thread. Knowing this now, it makes more sense and I've since resolved the issue :) No error, slot has been added and all works as intended. Do keep in mind that I'm going into these APIs entirely blind so I'm unfamiliar with them. What may seem simple to you in Forge 1.14 I have yet to learn. I appreciate the assistance.

 

I needed an instance of the horse from both the container and the screen when registering the slot in order to grab its capabilities, so that as well I had to retrieve reflectively. With all those changes being made, I've finalized on the following (and will be making changes to ensure the reflection is properly cached).

    private static final ResourceLocation HORSE_GUI_TEXTURES = new ResourceLocation("textures/gui/container/horse.png");
    private static final Function<IItemHandler, Slot> SLOT_CREATOR = i -> new SlotItemHandler(i, 0, 8, 54);

    @SubscribeEvent
    public static void attachHorseCapabilities(AttachCapabilitiesEvent<Entity> event) {
        if (event.getObject() instanceof AbstractHorseEntity) {
            event.addCapability(new ResourceLocation(MOD_ID, "my_custom_capability_id"), new MyCustomIItemHandlerProvider());
        }
    }
    
    @SubscribeEvent
    public static void addSlotServerSide(PlayerContainerEvent.Open event) {
        Container container = event.getContainer();
        if (container instanceof HorseInventoryContainer) {
            AbstractHorseEntity horse = getHorseFromField(container, "horse");
            IItemHandler itemHandler = horse.getCapability(MyCustomCapabilities.MY_CUSTOM_CAPABILITY).orElseThrow(IllegalStateException::new);

            addSlotToHorseContainer((HorseInventoryContainer) container, itemHandler, SLOT_CREATOR);
        }
    }
    
    @SubscribeEvent
    public static void addSlotClientSide(GuiOpenEvent event) {
        Screen screen = event.getGui();
        if (screen instanceof HorseInventoryScreen) {
            AbstractHorseEntity horse = getHorseFromField(screen, "horseEntity");
            IItemHandler itemHandler = horse.getCapability(MyCustomCapabilities.MY_CUSTOM_CAPABILITY).orElseThrow(IllegalStateException::new);

            addSlotToHorseContainer(((HorseInventoryScreen) screen).getContainer(), itemHandler, SLOT_CREATOR);
        }
    }
    
    @SubscribeEvent
    public static void renderExtraSlot(GuiContainerEvent.DrawBackground event) {
        ContainerScreen<?> screen = event.getGuiContainer();
        if (screen instanceof HorseInventoryScreen) {
            GlStateManager.color4f(1.0F, 1.0F, 1.0F, 1.0F);
            Minecraft.getInstance().getTextureManager().bindTexture(HORSE_GUI_TEXTURES);
            
            int ySize = screen.getYSize();
            int i = (screen.width - screen.getXSize()) / 2;
            int j = (screen.height - ySize) / 2;

            // screen x, screen y, texture x, texture y, width, height
            screen.blit(i + 7, j + 53, 0, ySize, 18, 18);
        }
    }
    
    private static void addSlotToHorseContainer(HorseInventoryContainer container, IItemHandler handler, Function<IItemHandler, Slot> slotCreator) {
        try {
            Method methodAddSlot = Container.class.getDeclaredMethod("addSlot", Slot.class);
            methodAddSlot.setAccessible(true);
            methodAddSlot.invoke(container, slotCreator.apply(handler));
        } catch (ReflectiveOperationException e) {
            e.printStackTrace();
        }
    }
    
    private static AbstractHorseEntity getHorseFromField(Object instance, String fieldName) {
        try {
            Field field = instance.getClass().getDeclaredField(fieldName);
            return (AbstractHorseEntity) ReflectionUtil.getFieldValue(field, instance);
        } catch (ReflectiveOperationException e) {
            e.printStackTrace();
        }
        
        return null;
    }

}

If, aside from reflection caching, there is anything you feel needs changing, I'm open to critiques. Of course the name of my mod and a few classes were renamed. "MyCustomCapabilities" and other obviously poorly named classes and constants are named much more appropriately.

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