Support placing pocket computers on lecterns (#2098)

This allows shift+clicking a pocket computer on to a lectern. These
computers can be right clicked, opening the no-term computer GUI.
Terminal contents is rendered in-world, and broadcast to everyone in
range.

 - Add a new lectern PocketHolder.
 - Refactor some of the `PocketItemComputer` code to allow ticking pocket
   computers from a non-player/entity source.
 - Add a new model for pocket computers. This requires several new
   textures (somewhat mirroring the item ones), which is a little
   unfortunate, but looks much better than reusing the map renderer or
   item form.

projects/common/src/client/java/dan200/computercraft/client/model/LecternPocketModel.java

@@ -0,0 +1,96 @@
+// SPDX-FileCopyrightText: 2024 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package dan200.computercraft.client.model;
+
+import com.mojang.blaze3d.vertex.PoseStack;
+import com.mojang.blaze3d.vertex.VertexConsumer;
+import dan200.computercraft.api.ComputerCraftAPI;
+import dan200.computercraft.client.pocket.PocketComputerData;
+import dan200.computercraft.client.render.CustomLecternRenderer;
+import dan200.computercraft.shared.computer.core.ComputerFamily;
+import dan200.computercraft.shared.pocket.items.PocketComputerItem;
+import net.minecraft.client.model.geom.ModelPart;
+import net.minecraft.client.model.geom.PartPose;
+import net.minecraft.client.model.geom.builders.CubeListBuilder;
+import net.minecraft.client.model.geom.builders.MeshDefinition;
+import net.minecraft.client.renderer.LightTexture;
+import net.minecraft.client.renderer.MultiBufferSource;
+import net.minecraft.client.renderer.RenderType;
+import net.minecraft.client.resources.model.Material;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.util.FastColor;
+import net.minecraft.world.inventory.InventoryMenu;
+
+/**
+ * A model for {@linkplain PocketComputerItem pocket computers} placed on a lectern.
+ *
+ * @see CustomLecternRenderer
+ */
+public class LecternPocketModel {
+    public static final ResourceLocation TEXTURE_NORMAL = new ResourceLocation(ComputerCraftAPI.MOD_ID, "entity/pocket_computer_normal");
+    public static final ResourceLocation TEXTURE_ADVANCED = new ResourceLocation(ComputerCraftAPI.MOD_ID, "entity/pocket_computer_advanced");
+    public static final ResourceLocation TEXTURE_COLOUR = new ResourceLocation(ComputerCraftAPI.MOD_ID, "entity/pocket_computer_colour");
+    public static final ResourceLocation TEXTURE_FRAME = new ResourceLocation(ComputerCraftAPI.MOD_ID, "entity/pocket_computer_frame");
+    public static final ResourceLocation TEXTURE_LIGHT = new ResourceLocation(ComputerCraftAPI.MOD_ID, "entity/pocket_computer_light");
+
+    private static final Material MATERIAL_NORMAL = new Material(InventoryMenu.BLOCK_ATLAS, TEXTURE_NORMAL);
+    private static final Material MATERIAL_ADVANCED = new Material(InventoryMenu.BLOCK_ATLAS, TEXTURE_ADVANCED);
+    private static final Material MATERIAL_COLOUR = new Material(InventoryMenu.BLOCK_ATLAS, TEXTURE_COLOUR);
+    private static final Material MATERIAL_FRAME = new Material(InventoryMenu.BLOCK_ATLAS, TEXTURE_FRAME);
+    private static final Material MATERIAL_LIGHT = new Material(InventoryMenu.BLOCK_ATLAS, TEXTURE_LIGHT);
+
+    // The size of the terminal within the model.
+    public static final float TERM_WIDTH = 12.0f / 32.0f;
+    public static final float TERM_HEIGHT = 14.0f / 32.0f;
+
+    // The size of the texture. The texture is 36x36, but is at 2x resolution.
+    private static final int TEXTURE_WIDTH = 36 / 2;
+    private static final int TEXTURE_HEIGHT = 36 / 2;
+
+    private final ModelPart root;
+
+    public LecternPocketModel() {
+        root = buildPages();
+    }
+
+    private static ModelPart buildPages() {
+        var mesh = new MeshDefinition();
+        var parts = mesh.getRoot();
+        parts.addOrReplaceChild(
+            "root",
+            CubeListBuilder.create().texOffs(0, 0).addBox(0f, -5.0f, -4.0f, 1f, 10.0f, 8.0f),
+            PartPose.ZERO
+        );
+        return mesh.getRoot().bake(TEXTURE_WIDTH, TEXTURE_HEIGHT);
+    }
+
+    private void render(PoseStack poseStack, VertexConsumer buffer, int packedLight, int packedOverlay, int colour) {
+        int red = FastColor.ARGB32.red(colour), green = FastColor.ARGB32.green(colour), blue = FastColor.ARGB32.blue(colour), alpha = FastColor.ARGB32.alpha(colour);
+        root.render(poseStack, buffer, packedLight, packedOverlay, red / 255.0f, green / 255.0f, blue / 255.0f, alpha / 255.0f);
+    }
+
+    /**
+     * Render the pocket computer model.
+     *
+     * @param poseStack     The current pose stack.
+     * @param bufferSource  The buffer source to draw to.
+     * @param packedLight   The current light level.
+     * @param packedOverlay The overlay texture (used for entity hurt animation).
+     * @param family        The computer family.
+     * @param frameColour   The pocket computer's {@linkplain PocketComputerItem#getColour(ItemStack) colour}.
+     * @param lightColour   The pocket computer's {@linkplain PocketComputerData#getLightState() light colour}.
+     */
+    public void render(PoseStack poseStack, MultiBufferSource bufferSource, int packedLight, int packedOverlay, ComputerFamily family, int frameColour, int lightColour) {
+        if (frameColour != -1) {
+            root.render(poseStack, MATERIAL_FRAME.buffer(bufferSource, RenderType::entityCutout), packedLight, packedOverlay, 1, 1, 1, 1);
+            render(poseStack, MATERIAL_COLOUR.buffer(bufferSource, RenderType::entityCutout), packedLight, packedOverlay, frameColour);
+        } else {
+            var buffer = (family == ComputerFamily.ADVANCED ? MATERIAL_ADVANCED : MATERIAL_NORMAL).buffer(bufferSource, RenderType::entityCutout);
+            root.render(poseStack, buffer, packedLight, packedOverlay, 1, 1, 1, 1);
+        }
+
+        render(poseStack, MATERIAL_LIGHT.buffer(bufferSource, RenderType::entityCutout), LightTexture.FULL_BRIGHT, packedOverlay, lightColour);
+    }
+}

projects/common/src/client/java/dan200/computercraft/client/render/CustomLecternRenderer.java

@@ -6,15 +6,28 @@ package dan200.computercraft.client.render;
 
 import com.mojang.blaze3d.vertex.PoseStack;
 import com.mojang.math.Axis;
+import dan200.computercraft.client.model.LecternPocketModel;
 import dan200.computercraft.client.model.LecternPrintoutModel;
+import dan200.computercraft.client.pocket.ClientPocketComputers;
+import dan200.computercraft.client.render.text.FixedWidthFontRenderer;
+import dan200.computercraft.core.terminal.Terminal;
+import dan200.computercraft.core.util.Colour;
 import dan200.computercraft.shared.lectern.CustomLecternBlockEntity;
 import dan200.computercraft.shared.media.items.PrintoutItem;
+import dan200.computercraft.shared.pocket.items.PocketComputerItem;
+import dan200.computercraft.shared.util.ARGB32;
 import net.minecraft.client.renderer.MultiBufferSource;
 import net.minecraft.client.renderer.RenderType;
+import net.minecraft.client.renderer.blockentity.BlockEntityRenderDispatcher;
 import net.minecraft.client.renderer.blockentity.BlockEntityRenderer;
 import net.minecraft.client.renderer.blockentity.BlockEntityRendererProvider;
 import net.minecraft.client.renderer.blockentity.LecternRenderer;
 import net.minecraft.world.level.block.LecternBlock;
+import net.minecraft.world.phys.Vec3;
+
+import static dan200.computercraft.client.render.ComputerBorderRenderer.MARGIN;
+import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.FONT_HEIGHT;
+import static dan200.computercraft.client.render.text.FixedWidthFontRenderer.FONT_WIDTH;
 
 /**
  * A block entity renderer for our {@linkplain CustomLecternBlockEntity lectern}.
@@ -22,10 +35,17 @@ import net.minecraft.world.level.block.LecternBlock;
  * This largely follows {@link LecternRenderer}, but with support for multiple types of item.
  */
 public class CustomLecternRenderer implements BlockEntityRenderer<CustomLecternBlockEntity> {
+    private static final int POCKET_TERMINAL_RENDER_DISTANCE = 32;
+
+    private final BlockEntityRenderDispatcher berDispatcher;
     private final LecternPrintoutModel printoutModel;
+    private final LecternPocketModel pocketModel;
 
     public CustomLecternRenderer(BlockEntityRendererProvider.Context context) {
+        berDispatcher = context.getBlockEntityRenderDispatcher();
+
         printoutModel = new LecternPrintoutModel();
+        pocketModel = new LecternPocketModel();
     }
 
     @Override
@@ -44,8 +64,46 @@ public class CustomLecternRenderer implements BlockEntityRenderer<CustomLecternB
             } else {
                 printoutModel.renderPages(poseStack, vertexConsumer, packedLight, packedOverlay, PrintoutItem.getPageCount(item));
             }
+        } else if (item.getItem() instanceof PocketComputerItem pocket) {
+            var computer = ClientPocketComputers.get(item);
+
+            pocketModel.render(
+                poseStack, buffer, packedLight, packedOverlay, pocket.getFamily(), pocket.getColour(item),
+                ARGB32.opaque(computer == null || computer.getLightState() == -1 ? Colour.BLACK.getHex() : computer.getLightState())
+            );
+
+            // Jiggle the terminal about a bit, so (0, 0) is in the top left of the model's terminal hole.
+            poseStack.mulPose(Axis.YP.rotationDegrees(90f));
+            poseStack.translate(-0.5 * LecternPocketModel.TERM_WIDTH, 0.5 * LecternPocketModel.TERM_HEIGHT + 1f / 32.0f, 1 / 16.0f);
+            poseStack.mulPose(Axis.XP.rotationDegrees(180));
+
+            // Either render the terminal or a black screen, depending on how close we are.
+            var terminal = computer == null ? null : computer.getTerminal();
+            var quadEmitter = FixedWidthFontRenderer.toVertexConsumer(poseStack, buffer.getBuffer(RenderTypes.TERMINAL));
+            if (terminal != null && Vec3.atCenterOf(lectern.getBlockPos()).closerThan(berDispatcher.camera.getPosition(), POCKET_TERMINAL_RENDER_DISTANCE)) {
+                renderPocketTerminal(poseStack, quadEmitter, terminal);
+            } else {
+                FixedWidthFontRenderer.drawEmptyTerminal(quadEmitter, 0, 0, LecternPocketModel.TERM_WIDTH, LecternPocketModel.TERM_HEIGHT);
+            }
         }
 
         poseStack.popPose();
     }
+
+    private static void renderPocketTerminal(PoseStack poseStack, FixedWidthFontRenderer.QuadEmitter quadEmitter, Terminal terminal) {
+        var width = terminal.getWidth() * FONT_WIDTH;
+        var height = terminal.getHeight() * FONT_HEIGHT;
+
+        // Scale the terminal down to fit in the available space.
+        var scaleX = LecternPocketModel.TERM_WIDTH / (width + MARGIN * 2);
+        var scaleY = LecternPocketModel.TERM_HEIGHT / (height + MARGIN * 2);
+        var scale = Math.min(scaleX, scaleY);
+        poseStack.scale(scale, scale, -1.0f);
+
+        // Convert the model dimensions to terminal space, then find out how large the margin should be.
+        var marginX = ((LecternPocketModel.TERM_WIDTH / scale) - width) / 2;
+        var marginY = ((LecternPocketModel.TERM_HEIGHT / scale) - height) / 2;
+
+        FixedWidthFontRenderer.drawTerminal(quadEmitter, marginX, marginY, terminal, marginY, marginY, marginX, marginX);
+    }
 }

projects/common/src/client/java/dan200/computercraft/client/render/text/FixedWidthFontRenderer.java

@@ -43,7 +43,7 @@ public final class FixedWidthFontRenderer {
     static final float BACKGROUND_END = (WIDTH - 4.0f) / WIDTH;
 
     private static final int BLACK = FastColor.ARGB32.color(255, byteColour(Colour.BLACK.getR()), byteColour(Colour.BLACK.getR()), byteColour(Colour.BLACK.getR()));
-    private static final float Z_OFFSET = 1e-3f;
+    private static final float Z_OFFSET = 1e-4f;
 
     private FixedWidthFontRenderer() {
     }

projects/common/src/datagen/java/dan200/computercraft/data/DataProviders.java

@@ -6,6 +6,7 @@ package dan200.computercraft.data;
 
 import com.mojang.serialization.Codec;
 import dan200.computercraft.client.gui.GuiSprites;
+import dan200.computercraft.client.model.LecternPocketModel;
 import dan200.computercraft.client.model.LecternPrintoutModel;
 import dan200.computercraft.shared.turtle.inventory.UpgradeSlot;
 import net.minecraft.client.renderer.texture.atlas.SpriteSource;
@@ -54,7 +55,9 @@ public final class DataProviders {
             out.accept(new ResourceLocation("blocks"), makeSprites(Stream.of(
                 UpgradeSlot.LEFT_UPGRADE,
                 UpgradeSlot.RIGHT_UPGRADE,
-                LecternPrintoutModel.TEXTURE
+                LecternPrintoutModel.TEXTURE,
+                LecternPocketModel.TEXTURE_NORMAL, LecternPocketModel.TEXTURE_ADVANCED,
+                LecternPocketModel.TEXTURE_COLOUR, LecternPocketModel.TEXTURE_FRAME, LecternPocketModel.TEXTURE_LIGHT
             )));
             out.accept(GuiSprites.SPRITE_SHEET, makeSprites(
                 Stream.of(GuiSprites.TURTLE_NORMAL_SELECTED_SLOT, GuiSprites.TURTLE_ADVANCED_SELECTED_SLOT),

projects/common/src/generated/resources/assets/minecraft/atlases/blocks.json

@@ -2,6 +2,11 @@
   "sources": [
     {"type": "minecraft:single", "resource": "computercraft:gui/turtle_upgrade_left"},
     {"type": "minecraft:single", "resource": "computercraft:gui/turtle_upgrade_right"},
-    {"type": "minecraft:single", "resource": "computercraft:entity/printout"}
+    {"type": "minecraft:single", "resource": "computercraft:entity/printout"},
+    {"type": "minecraft:single", "resource": "computercraft:entity/pocket_computer_normal"},
+    {"type": "minecraft:single", "resource": "computercraft:entity/pocket_computer_advanced"},
+    {"type": "minecraft:single", "resource": "computercraft:entity/pocket_computer_colour"},
+    {"type": "minecraft:single", "resource": "computercraft:entity/pocket_computer_frame"},
+    {"type": "minecraft:single", "resource": "computercraft:entity/pocket_computer_light"}
   ]
 }

projects/common/src/main/java/dan200/computercraft/shared/lectern/CustomLecternBlock.java

@@ -6,6 +6,7 @@ package dan200.computercraft.shared.lectern;
 
 import dan200.computercraft.shared.ModRegistry;
 import dan200.computercraft.shared.media.items.PrintoutItem;
+import dan200.computercraft.shared.util.BlockEntityHelpers;
 import net.minecraft.core.BlockPos;
 import net.minecraft.server.level.ServerLevel;
 import net.minecraft.stats.Stats;
@@ -14,6 +15,7 @@ import net.minecraft.world.InteractionHand;
 import net.minecraft.world.InteractionResult;
 import net.minecraft.world.entity.item.ItemEntity;
 import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.item.Item;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
 import net.minecraft.world.item.context.UseOnContext;
@@ -21,8 +23,12 @@ import net.minecraft.world.level.BlockGetter;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.level.block.Blocks;
 import net.minecraft.world.level.block.LecternBlock;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import net.minecraft.world.level.block.entity.BlockEntityTicker;
+import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.phys.BlockHitResult;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * Extends {@link LecternBlock} with support for {@linkplain PrintoutItem printouts}.
@@ -55,6 +61,27 @@ public class CustomLecternBlock extends LecternBlock {
         if (level.getBlockEntity(pos) instanceof CustomLecternBlockEntity be) be.setItem(item.split(1));
     }
 
+    /**
+     * A default implementation of {@link Item#useOn(UseOnContext)} for items that can be placed on a lectern.
+     *
+     * @param context The context of this item usage action.
+     * @return Whether the item was placed or not.
+     */
+    public static InteractionResult defaultUseItemOn(UseOnContext context) {
+        var level = context.getLevel();
+        var blockPos = context.getClickedPos();
+        var blockState = level.getBlockState(blockPos);
+        if (blockState.is(Blocks.LECTERN) && !blockState.getValue(LecternBlock.HAS_BOOK)) {
+            // If we have an empty lectern, place our book into it.
+            if (!level.isClientSide) {
+                CustomLecternBlock.replaceLectern(level, blockPos, blockState, context.getItemInHand());
+            }
+            return InteractionResult.sidedSuccess(level.isClientSide);
+        } else {
+            return InteractionResult.PASS;
+        }
+    }
+
     /**
      * Remove a custom lectern and replace it with an empty vanilla one.
      *
@@ -131,7 +158,7 @@ public class CustomLecternBlock extends LecternBlock {
                 clearLectern(level, pos, state);
             } else {
                 // Otherwise open the screen.
-                player.openMenu(lectern);
+                lectern.openMenu(player);
             }
 
             player.awardStat(Stats.INTERACT_WITH_LECTERN);
@@ -139,4 +166,11 @@ public class CustomLecternBlock extends LecternBlock {
 
         return InteractionResult.sidedSuccess(level.isClientSide);
     }
+
+    @Override
+    public @Nullable <T extends BlockEntity> BlockEntityTicker<T> getTicker(Level level, BlockState state, BlockEntityType<T> type) {
+        return level.isClientSide ? null : BlockEntityHelpers.createTickerHelper(type, ModRegistry.BlockEntities.LECTERN.get(), serverTicker);
+    }
+
+    private static final BlockEntityTicker<CustomLecternBlockEntity> serverTicker = (level, pos, state, lectern) -> lectern.tick();
 }

projects/common/src/main/java/dan200/computercraft/shared/lectern/CustomLecternBlockEntity.java

@@ -9,27 +9,25 @@ import dan200.computercraft.shared.container.BasicContainer;
 import dan200.computercraft.shared.container.SingleContainerData;
 import dan200.computercraft.shared.media.PrintoutMenu;
 import dan200.computercraft.shared.media.items.PrintoutItem;
+import dan200.computercraft.shared.pocket.core.PocketHolder;
+import dan200.computercraft.shared.pocket.items.PocketComputerItem;
 import dan200.computercraft.shared.util.BlockEntityHelpers;
 import net.minecraft.core.BlockPos;
 import net.minecraft.nbt.CompoundTag;
 import net.minecraft.nbt.Tag;
-import net.minecraft.network.chat.Component;
 import net.minecraft.network.protocol.Packet;
 import net.minecraft.network.protocol.game.ClientGamePacketListener;
 import net.minecraft.network.protocol.game.ClientboundBlockEntityDataPacket;
 import net.minecraft.util.Mth;
 import net.minecraft.world.Container;
-import net.minecraft.world.MenuProvider;
+import net.minecraft.world.SimpleMenuProvider;
-import net.minecraft.world.entity.player.Inventory;
 import net.minecraft.world.entity.player.Player;
-import net.minecraft.world.inventory.AbstractContainerMenu;
 import net.minecraft.world.inventory.ContainerData;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.block.LecternBlock;
 import net.minecraft.world.level.block.entity.BlockEntity;
 import net.minecraft.world.level.block.entity.LecternBlockEntity;
 import net.minecraft.world.level.block.state.BlockState;
-import org.jetbrains.annotations.Nullable;
 
 import java.util.AbstractList;
 import java.util.List;
@@ -39,7 +37,7 @@ import java.util.List;
  *
  * @see LecternBlockEntity
  */
-public final class CustomLecternBlockEntity extends BlockEntity implements MenuProvider {
+public final class CustomLecternBlockEntity extends BlockEntity {
     private static final String NBT_ITEM = "Item";
     private static final String NBT_PAGE = "Page";
 
@@ -81,6 +79,12 @@ public final class CustomLecternBlockEntity extends BlockEntity implements MenuP
         }
     }
 
+    void tick() {
+        if (item.getItem() instanceof PocketComputerItem pocket) {
+            pocket.tick(item, new PocketHolder.LecternHolder(this), false);
+        }
+    }
+
     /**
      * Set the current page, emitting a redstone pulse if needed.
      *
@@ -123,24 +127,17 @@ public final class CustomLecternBlockEntity extends BlockEntity implements MenuP
         return tag;
     }
 
-    @Nullable
+    void openMenu(Player player) {
-    @Override
-    public AbstractContainerMenu createMenu(int containerId, Inventory playerInventory, Player player) {
         var item = getItem();
         if (item.getItem() instanceof PrintoutItem) {
-            return new PrintoutMenu(
+            player.openMenu(new SimpleMenuProvider((id, inventory, entity) -> new PrintoutMenu(
-                containerId, new LecternContainer(), 0,
+                id, new LecternContainer(), 0,
-                p -> Container.stillValidBlockEntity(this, player, Container.DEFAULT_DISTANCE_LIMIT),
+                p -> Container.stillValidBlockEntity(this, p, Container.DEFAULT_DISTANCE_LIMIT),
                 new PrintoutContainerData()
-            );
+            ), getItem().getDisplayName()));
+        } else if (item.getItem() instanceof PocketComputerItem pocket) {
+            pocket.open(player, item, new PocketHolder.LecternHolder(this), true);
         }
-
-        return null;
-    }
-
-    @Override
-    public Component getDisplayName() {
-        return getItem().getDisplayName();
     }
 
     /**

projects/common/src/main/java/dan200/computercraft/shared/media/items/PrintoutItem.java

@@ -19,8 +19,6 @@ import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.TooltipFlag;
 import net.minecraft.world.item.context.UseOnContext;
 import net.minecraft.world.level.Level;
-import net.minecraft.world.level.block.Blocks;
-import net.minecraft.world.level.block.LecternBlock;
 
 import javax.annotation.Nullable;
 import java.util.List;
@@ -56,18 +54,7 @@ public class PrintoutItem extends Item {
 
     @Override
     public InteractionResult useOn(UseOnContext context) {
-        var level = context.getLevel();
+        return CustomLecternBlock.defaultUseItemOn(context);
-        var blockPos = context.getClickedPos();
-        var blockState = level.getBlockState(blockPos);
-        if (blockState.is(Blocks.LECTERN) && !blockState.getValue(LecternBlock.HAS_BOOK)) {
-            // If we have an empty lectern, place our book into it.
-            if (!level.isClientSide) {
-                CustomLecternBlock.replaceLectern(level, blockPos, blockState, context.getItemInHand());
-            }
-            return InteractionResult.sidedSuccess(level.isClientSide);
-        } else {
-            return InteractionResult.PASS;
-        }
     }
 
     @Override

projects/common/src/main/java/dan200/computercraft/shared/pocket/core/PocketHolder.java

@@ -5,7 +5,9 @@
 package dan200.computercraft.shared.pocket.core;
 
 import dan200.computercraft.shared.computer.core.ServerComputer;
+import dan200.computercraft.shared.lectern.CustomLecternBlockEntity;
 import dan200.computercraft.shared.pocket.items.PocketComputerItem;
+import dan200.computercraft.shared.util.BlockEntityHelpers;
 import net.minecraft.core.BlockPos;
 import net.minecraft.server.level.ServerLevel;
 import net.minecraft.server.level.ServerPlayer;
@@ -51,6 +53,15 @@ public sealed interface PocketHolder {
      */
     void setChanged();
 
+    /**
+     * Whether the terminal is visible to all players in range, and so should be broadcast to everyone.
+     *
+     * @return Whether to send the terminal.
+     */
+    default boolean isTerminalAlwaysVisible() {
+        return false;
+    }
+
     /**
      * An {@link Entity} holding a pocket computer.
      */
@@ -112,4 +123,41 @@ public sealed interface PocketHolder {
             entity.setItem(entity.getItem().copy());
         }
     }
+
+    /**
+     * A pocket computer in a {@link CustomLecternBlockEntity}.
+     *
+     * @param lectern The lectern holding this item.
+     */
+    record LecternHolder(CustomLecternBlockEntity lectern) implements PocketHolder {
+        @Override
+        public ServerLevel level() {
+            return (ServerLevel) lectern.getLevel();
+        }
+
+        @Override
+        public Vec3 pos() {
+            return Vec3.atCenterOf(lectern.getBlockPos());
+        }
+
+        @Override
+        public BlockPos blockPos() {
+            return lectern.getBlockPos();
+        }
+
+        @Override
+        public boolean isValid(ServerComputer computer) {
+            return !lectern().isRemoved() && PocketComputerItem.isServerComputer(computer, lectern.getItem());
+        }
+
+        @Override
+        public void setChanged() {
+            BlockEntityHelpers.updateBlock(lectern());
+        }
+
+        @Override
+        public boolean isTerminalAlwaysVisible() {
+            return true;
+        }
+    }
 }

projects/common/src/main/java/dan200/computercraft/shared/pocket/core/PocketServerComputer.java

@@ -72,7 +72,7 @@ public final class PocketServerComputer extends ServerComputer {
             // Broadcast the state to new players.
             var added = newTracking.stream().filter(x -> !tracking.contains(x)).toList();
             if (!added.isEmpty()) {
-                ServerNetworking.sendToPlayers(new PocketComputerDataMessage(this, false), added);
+                ServerNetworking.sendToPlayers(new PocketComputerDataMessage(this, brain.holder().isTerminalAlwaysVisible()), added);
             }
         }
 
@@ -83,9 +83,15 @@ public final class PocketServerComputer extends ServerComputer {
     protected void onTerminalChanged() {
         super.onTerminalChanged();
 
-        if (brain.holder() instanceof PocketHolder.PlayerHolder holder && holder.isValid(this)) {
+        var holder = brain.holder() instanceof PocketHolder.PlayerHolder h && h.isValid(this) ? h.entity() : null;
-            // Broadcast the terminal to the current player.
+        if (brain.holder().isTerminalAlwaysVisible() && !tracking.isEmpty()) {
-            ServerNetworking.sendToPlayer(new PocketComputerDataMessage(this, true), holder.entity());
+            // If the terminal is always visible, send it to all players *and* the holder.
+            var packet = new PocketComputerDataMessage(this, true);
+            ServerNetworking.sendToPlayers(packet, tracking);
+            if (holder != null && !tracking.contains(holder)) ServerNetworking.sendToPlayer(packet, holder);
+        } else if (holder != null) {
+            // Otherwise just send it to the holder.
+            ServerNetworking.sendToPlayer(new PocketComputerDataMessage(this, true), holder);
         }
     }
 

projects/common/src/main/java/dan200/computercraft/shared/pocket/items/PocketComputerItem.java

@@ -21,6 +21,7 @@ import dan200.computercraft.shared.computer.core.ServerContext;
 import dan200.computercraft.shared.computer.inventory.ComputerMenuWithoutInventory;
 import dan200.computercraft.shared.computer.items.IComputerItem;
 import dan200.computercraft.shared.config.Config;
+import dan200.computercraft.shared.lectern.CustomLecternBlock;
 import dan200.computercraft.shared.network.container.ComputerContainerData;
 import dan200.computercraft.shared.platform.PlatformHelper;
 import dan200.computercraft.shared.pocket.core.PocketBrain;
@@ -44,6 +45,7 @@ import net.minecraft.world.entity.player.Player;
 import net.minecraft.world.item.Item;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.TooltipFlag;
+import net.minecraft.world.item.context.UseOnContext;
 import net.minecraft.world.level.Level;
 
 import javax.annotation.Nullable;
@@ -83,10 +85,18 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
      *
      * @param stack   The current pocket computer stack.
      * @param holder  The entity holding the pocket item.
-     * @param brain  The pocket computer brain.
+     * @param passive If set, the pocket computer will not be created if it doesn't exist, and will not be kept alive.
      */
-    private void tick(ItemStack stack, PocketHolder holder, PocketBrain brain) {
+    public void tick(ItemStack stack, PocketHolder holder, boolean passive) {
-        brain.updateHolder(holder);
+        PocketBrain brain;
+        if (passive) {
+            var computer = getServerComputer(holder.level().getServer(), stack);
+            if (computer == null) return;
+            brain = computer.getBrain();
+        } else {
+            brain = getOrCreateBrain(holder.level(), holder, stack);
+            brain.computer().keepAlive();
+        }
 
         // Update pocket upgrade
         var upgrade = brain.getUpgrade();
@@ -139,11 +149,7 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
         if (slot < 0) return;
 
         // If we're in the inventory, create a computer and keep it alive.
-        var holder = new PocketHolder.PlayerHolder(player, slot);
+        tick(stack, new PocketHolder.PlayerHolder(player, slot), false);
-        var brain = getOrCreateBrain((ServerLevel) world, holder, stack);
-        brain.computer().keepAlive();
-
-        tick(stack, holder, brain);
     }
 
     @ForgeOverride
@@ -153,12 +159,16 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
 
         // If we're an item entity, tick an already existing computer (as to update the position), but do not keep the
         // computer alive.
-        var computer = getServerComputer(level.getServer(), stack);
+        tick(stack, new PocketHolder.ItemEntityHolder(entity), true);
-        if (computer != null) tick(stack, new PocketHolder.ItemEntityHolder(entity), computer.getBrain());
 
         return false;
     }
 
+    @Override
+    public InteractionResult useOn(UseOnContext context) {
+        return CustomLecternBlock.defaultUseItemOn(context);
+    }
+
     @Override
     public InteractionResultHolder<ItemStack> use(Level world, Player player, InteractionHand hand) {
         var stack = player.getItemInHand(hand);
@@ -171,25 +181,39 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
             var stop = false;
             var upgrade = getUpgrade(stack);
             if (upgrade != null) {
-                brain.updateHolder(holder);
                 stop = upgrade.onRightClick(world, brain, computer.getPeripheral(ComputerSide.BACK));
                 // Sync back just in case. We don't need to setChanged, as we'll return the item anyway.
                 updateItem(stack, brain);
             }
 
-            if (!stop) {
+            if (!stop) openImpl(player, stack, holder, hand == InteractionHand.OFF_HAND, computer);
-                PlatformHelper.get().openMenu(
-                    player, stack.getHoverName(),
-                    (id, inventory, entity) -> new ComputerMenuWithoutInventory(
-                        hand == InteractionHand.OFF_HAND ? ModRegistry.Menus.POCKET_COMPUTER_NO_TERM.get() : ModRegistry.Menus.COMPUTER.get(),
-                        id, inventory, p -> isServerComputer(computer, p.getItemInHand(hand)), computer
-                    ),
-                    new ComputerContainerData(computer, stack));
-            }
         }
         return new InteractionResultHolder<>(InteractionResult.sidedSuccess(world.isClientSide), stack);
     }
 
+    /**
+     * Open a container for this pocket computer.
+     *
+     * @param player       The player to show the menu for.
+     * @param stack        The pocket computer stack.
+     * @param holder       The holder of the pocket computer.
+     * @param isTypingOnly Open the off-hand pocket screen (only supporting typing, with no visible terminal).
+     */
+    public void open(Player player, ItemStack stack, PocketHolder holder, boolean isTypingOnly) {
+        var brain = getOrCreateBrain(holder.level(), holder, stack);
+        var computer = brain.computer();
+        computer.turnOn();
+        openImpl(player, stack, holder, isTypingOnly, computer);
+    }
+
+    private static void openImpl(Player player, ItemStack stack, PocketHolder holder, boolean isTypingOnly, ServerComputer computer) {
+        PlatformHelper.get().openMenu(player, stack.getHoverName(), (id, inventory, entity) -> new ComputerMenuWithoutInventory(
+            isTypingOnly ? ModRegistry.Menus.POCKET_COMPUTER_NO_TERM.get() : ModRegistry.Menus.COMPUTER.get(), id, inventory,
+            p -> holder.isValid(computer),
+            computer
+        ), new ComputerContainerData(computer, stack));
+    }
+
     @Override
     public Component getName(ItemStack stack) {
         var baseString = getDescriptionId(stack);
@@ -233,7 +257,11 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
         var registry = ServerContext.get(level.getServer()).registry();
         {
             var computer = getServerComputer(registry, stack);
-            if (computer != null) return computer.getBrain();
+            if (computer != null) {
+                var brain = computer.getBrain();
+                brain.updateHolder(holder);
+                return brain;
+            }
         }
 
         var computerID = getComputerID(stack);
@@ -252,8 +280,7 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
         tag.putInt(NBT_SESSION, registry.getSessionID());
         tag.putUUID(NBT_INSTANCE, computer.register());
 
-        // Only turn on when initially creating the computer, rather than each tick.
+        if (isMarkedOn(stack)) computer.turnOn();
-        if (isMarkedOn(stack) && holder instanceof PocketHolder.PlayerHolder) computer.turnOn();
 
         updateItem(stack, brain);