Allow placing printouts in lecterns

- Add a new custom lectern block, that is used to hold the printed
   pages. We have to roll quite a lot of custom logic, so this is much
   cleaner than trying to mixin to the existing lectern code.

 - Add a new (entity) model for printed pages and books placed on a
   lectern. I did originally think about just rendering the item (or the
   in-hand/map version), but I think this is a bit more consistent with
   vanilla.

   However, we do still need to sync the item to the client (mostly to
   get the current page count!). There is a risk of chunkbanning here,
   but I think it's much harder than vanilla, due to the significantly
   reduced page limit.

projects/common/src/client/java/dan200/computercraft/client/ClientRegistry.java

@@ -13,6 +13,7 @@ import dan200.computercraft.api.client.turtle.RegisterTurtleUpgradeModeller;
 import dan200.computercraft.api.client.turtle.TurtleUpgradeModeller;
 import dan200.computercraft.client.gui.*;
 import dan200.computercraft.client.pocket.ClientPocketComputers;
+import dan200.computercraft.client.render.CustomLecternRenderer;
 import dan200.computercraft.client.render.RenderTypes;
 import dan200.computercraft.client.render.TurtleBlockEntityRenderer;
 import dan200.computercraft.client.render.monitor.MonitorBlockEntityRenderer;
@@ -73,6 +74,7 @@ public final class ClientRegistry {
         BlockEntityRenderers.register(ModRegistry.BlockEntities.MONITOR_ADVANCED.get(), MonitorBlockEntityRenderer::new);
         BlockEntityRenderers.register(ModRegistry.BlockEntities.TURTLE_NORMAL.get(), TurtleBlockEntityRenderer::new);
         BlockEntityRenderers.register(ModRegistry.BlockEntities.TURTLE_ADVANCED.get(), TurtleBlockEntityRenderer::new);
+        BlockEntityRenderers.register(ModRegistry.BlockEntities.LECTERN.get(), CustomLecternRenderer::new);
     }
 
     /**

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

@@ -0,0 +1,117 @@
+// 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.render.CustomLecternRenderer;
+import dan200.computercraft.shared.media.items.PrintoutItem;
+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.resources.model.Material;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.inventory.InventoryMenu;
+
+import java.util.List;
+
+/**
+ * A model for {@linkplain PrintoutItem printouts} placed on a lectern.
+ * <p>
+ * This provides two models, {@linkplain #renderPages(PoseStack, VertexConsumer, int, int, int) one for a variable
+ * number of pages}, and {@linkplain #renderBook(PoseStack, VertexConsumer, int, int) one for books}.
+ *
+ * @see CustomLecternRenderer
+ */
+public class LecternPrintoutModel {
+    public static final ResourceLocation TEXTURE = new ResourceLocation(ComputerCraftAPI.MOD_ID, "entity/printout");
+    public static final Material MATERIAL = new Material(InventoryMenu.BLOCK_ATLAS, TEXTURE);
+
+    private static final int TEXTURE_WIDTH = 32;
+    private static final int TEXTURE_HEIGHT = 32;
+
+    private static final String PAGE_1 = "page_1";
+    private static final String PAGE_2 = "page_2";
+    private static final String PAGE_3 = "page_3";
+    private static final List<String> PAGES = List.of(PAGE_1, PAGE_2, PAGE_3);
+
+    private final ModelPart pagesRoot;
+    private final ModelPart bookRoot;
+    private final ModelPart[] pages;
+
+    public LecternPrintoutModel() {
+        pagesRoot = buildPages();
+        bookRoot = buildBook();
+        pages = PAGES.stream().map(pagesRoot::getChild).toArray(ModelPart[]::new);
+    }
+
+    private static ModelPart buildPages() {
+        var mesh = new MeshDefinition();
+        var parts = mesh.getRoot();
+        parts.addOrReplaceChild(
+            PAGE_1,
+            CubeListBuilder.create().texOffs(0, 0).addBox(-0.005f, -4.0f, -2.5f, 1f, 8.0f, 5.0f),
+            PartPose.ZERO
+        );
+
+        parts.addOrReplaceChild(
+            PAGE_2,
+            CubeListBuilder.create().texOffs(12, 0).addBox(-0.005f, -4.0f, -2.5f, 1f, 8.0f, 5.0f),
+            PartPose.offsetAndRotation(-0.125f, 0, 1.5f, (float) Math.PI * (1f / 16), 0, 0)
+        );
+        parts.addOrReplaceChild(
+            PAGE_3,
+            CubeListBuilder.create().texOffs(12, 0).addBox(-0.005f, -4.0f, -2.5f, 1f, 8.0f, 5.0f),
+            PartPose.offsetAndRotation(-0.25f, 0, -1.5f, (float) -Math.PI * (2f / 16), 0, 0)
+        );
+
+        return mesh.getRoot().bake(TEXTURE_WIDTH, TEXTURE_HEIGHT);
+    }
+
+    private static ModelPart buildBook() {
+        var mesh = new MeshDefinition();
+        var parts = mesh.getRoot();
+
+        parts.addOrReplaceChild(
+            "spine",
+            CubeListBuilder.create().texOffs(12, 15).addBox(-0.005f, -5.0f, -0.5f, 0, 10, 1.0f),
+            PartPose.ZERO
+        );
+
+        var angle = (float) Math.toRadians(5);
+        parts.addOrReplaceChild(
+            "left",
+            CubeListBuilder.create()
+                .texOffs(0, 10).addBox(0, -5.0f, -6.0f, 0, 10, 6.0f)
+                .texOffs(0, 0).addBox(0.005f, -4.0f, -5.0f, 1.0f, 8.0f, 5.0f),
+            PartPose.offsetAndRotation(-0.005f, 0, -0.5f, 0, -angle, 0)
+        );
+
+        parts.addOrReplaceChild(
+            "right",
+            CubeListBuilder.create()
+                .texOffs(14, 10).addBox(0, -5.0f, 0, 0, 10, 6.0f)
+                .texOffs(0, 0).addBox(0.005f, -4.0f, 0, 1.0f, 8.0f, 5.0f),
+            PartPose.offsetAndRotation(-0.005f, 0, 0.5f, 0, angle, 0)
+        );
+
+        return mesh.getRoot().bake(TEXTURE_WIDTH, TEXTURE_HEIGHT);
+    }
+
+    public void renderBook(PoseStack poseStack, VertexConsumer buffer, int packedLight, int packedOverlay) {
+        bookRoot.render(poseStack, buffer, packedLight, packedOverlay, 1, 1, 1, 1);
+    }
+
+    public void renderPages(PoseStack poseStack, VertexConsumer buffer, int packedLight, int packedOverlay, int pageCount) {
+        if (pageCount > pages.length) pageCount = pages.length;
+        var i = 0;
+        for (; i < pageCount; i++) pages[i].visible = true;
+        for (; i < pages.length; i++) pages[i].visible = false;
+
+        pagesRoot.render(poseStack, buffer, packedLight, packedOverlay, 1, 1, 1, 1);
+    }
+}

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

@@ -0,0 +1,51 @@
+// SPDX-FileCopyrightText: 2024 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package dan200.computercraft.client.render;
+
+import com.mojang.blaze3d.vertex.PoseStack;
+import com.mojang.math.Axis;
+import dan200.computercraft.client.model.LecternPrintoutModel;
+import dan200.computercraft.shared.lectern.CustomLecternBlockEntity;
+import dan200.computercraft.shared.media.items.PrintoutItem;
+import net.minecraft.client.renderer.MultiBufferSource;
+import net.minecraft.client.renderer.RenderType;
+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;
+
+/**
+ * A block entity renderer for our {@linkplain CustomLecternBlockEntity lectern}.
+ * <p>
+ * This largely follows {@link LecternRenderer}, but with support for multiple types of item.
+ */
+public class CustomLecternRenderer implements BlockEntityRenderer<CustomLecternBlockEntity> {
+    private final LecternPrintoutModel printoutModel;
+
+    public CustomLecternRenderer(BlockEntityRendererProvider.Context context) {
+        printoutModel = new LecternPrintoutModel();
+    }
+
+    @Override
+    public void render(CustomLecternBlockEntity lectern, float partialTick, PoseStack poseStack, MultiBufferSource buffer, int packedLight, int packedOverlay) {
+        poseStack.pushPose();
+        poseStack.translate(0.5f, 1.0625f, 0.5f);
+        poseStack.mulPose(Axis.YP.rotationDegrees(-lectern.getBlockState().getValue(LecternBlock.FACING).getClockWise().toYRot()));
+        poseStack.mulPose(Axis.ZP.rotationDegrees(67.5f));
+        poseStack.translate(0, -0.125f, 0);
+
+        var item = lectern.getItem();
+        if (item.getItem() instanceof PrintoutItem printout) {
+            var vertexConsumer = LecternPrintoutModel.MATERIAL.buffer(buffer, RenderType::entitySolid);
+            if (printout.getType() == PrintoutItem.Type.BOOK) {
+                printoutModel.renderBook(poseStack, vertexConsumer, packedLight, packedOverlay);
+            } else {
+                printoutModel.renderPages(poseStack, vertexConsumer, packedLight, packedOverlay, PrintoutItem.getPageCount(item));
+            }
+        }
+
+        poseStack.popPose();
+    }
+}

projects/common/src/client/java/dan200/computercraft/data/client/ClientDataProviders.java

@@ -5,6 +5,7 @@
 package dan200.computercraft.data.client;
 
 import dan200.computercraft.client.gui.GuiSprites;
+import dan200.computercraft.client.model.LecternPrintoutModel;
 import dan200.computercraft.data.DataProviders;
 import dan200.computercraft.shared.turtle.inventory.UpgradeSlot;
 import net.minecraft.client.renderer.texture.atlas.SpriteSource;
@@ -30,7 +31,8 @@ public final class ClientDataProviders {
         generator.addFromCodec("Block atlases", PackType.CLIENT_RESOURCES, "atlases", SpriteSources.FILE_CODEC, out -> {
             out.accept(new ResourceLocation("blocks"), List.of(
                 new SingleFile(UpgradeSlot.LEFT_UPGRADE, Optional.empty()),
-                new SingleFile(UpgradeSlot.RIGHT_UPGRADE, Optional.empty())
+                new SingleFile(UpgradeSlot.RIGHT_UPGRADE, Optional.empty()),
+                new SingleFile(LecternPrintoutModel.TEXTURE, Optional.empty())
             ));
             out.accept(GuiSprites.SPRITE_SHEET, Stream.of(
                 // Buttons

projects/common/src/generated/resources/assets/computercraft/blockstates/lectern.json

@@ -0,0 +1,8 @@
+{
+  "variants": {
+    "facing=east": {"model": "minecraft:block/lectern", "y": 90},
+    "facing=north": {"model": "minecraft:block/lectern", "y": 0},
+    "facing=south": {"model": "minecraft:block/lectern", "y": 180},
+    "facing=west": {"model": "minecraft:block/lectern", "y": 270}
+  }
+}

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

@@ -1,6 +1,7 @@
 {
   "sources": [
     {"type": "minecraft:single", "resource": "computercraft:gui/turtle_upgrade_left"},
-    {"type": "minecraft:single", "resource": "computercraft:gui/turtle_upgrade_right"}
+    {"type": "minecraft:single", "resource": "computercraft:gui/turtle_upgrade_right"},
+    {"type": "minecraft:single", "resource": "computercraft:entity/printout"}
   ]
 }

projects/common/src/generated/resources/data/computercraft/loot_tables/blocks/lectern.json

@@ -0,0 +1,12 @@
+{
+  "type": "minecraft:block",
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "conditions": [{"condition": "minecraft:survives_explosion"}],
+      "entries": [{"type": "minecraft:item", "name": "minecraft:lectern"}],
+      "rolls": 1.0
+    }
+  ],
+  "random_sequence": "computercraft:blocks/lectern"
+}

projects/common/src/main/java/dan200/computercraft/data/BlockModelProvider.java

@@ -23,6 +23,7 @@ import net.minecraft.data.models.BlockModelGenerators;
 import net.minecraft.data.models.blockstates.*;
 import net.minecraft.data.models.model.*;
 import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.level.block.Blocks;
 import net.minecraft.world.level.block.state.properties.BlockStateProperties;
 import net.minecraft.world.level.block.state.properties.BooleanProperty;
 import net.minecraft.world.level.block.state.properties.Property;
@@ -100,6 +101,11 @@ class BlockModelProvider {
         registerTurtleUpgrade(generators, "block/turtle_speaker", "block/turtle_speaker_face");
         registerTurtleModem(generators, "block/turtle_modem_normal", "block/wireless_modem_normal_face");
         registerTurtleModem(generators, "block/turtle_modem_advanced", "block/wireless_modem_advanced_face");
+
+        generators.blockStateOutput.accept(MultiVariantGenerator.multiVariant(
+            ModRegistry.Blocks.LECTERN.get(),
+            Variant.variant().with(VariantProperties.MODEL, ModelLocationUtils.getModelLocation(Blocks.LECTERN))
+        ).with(createHorizontalFacingDispatch()));
     }
 
     private static void registerDiskDrive(BlockModelGenerators generators) {

projects/common/src/main/java/dan200/computercraft/data/LanguageProvider.java

@@ -284,7 +284,9 @@ public final class LanguageProvider implements DataProvider {
         return Stream.of(
             RegistryWrappers.BLOCKS.stream()
                 .filter(x -> RegistryWrappers.BLOCKS.getKey(x).getNamespace().equals(ComputerCraftAPI.MOD_ID))
-                .map(Block::getDescriptionId),
+                .map(Block::getDescriptionId)
+                // Exclude blocks that just reuse vanilla translations, such as the lectern.
+                .filter(x -> !x.startsWith("block.minecraft.")),
             RegistryWrappers.ITEMS.stream()
                 .filter(x -> RegistryWrappers.ITEMS.getKey(x).getNamespace().equals(ComputerCraftAPI.MOD_ID))
                 .map(Item::getDescriptionId),

projects/common/src/main/java/dan200/computercraft/data/LootTableProvider.java

@@ -15,6 +15,7 @@ import dan200.computercraft.shared.peripheral.modem.wired.CableModemVariant;
 import net.minecraft.advancements.critereon.StatePropertiesPredicate;
 import net.minecraft.data.loot.LootTableProvider.SubProviderEntry;
 import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.item.Items;
 import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.storage.loot.LootPool;
 import net.minecraft.world.level.storage.loot.LootTable;
@@ -57,6 +58,8 @@ class LootTableProvider {
         computerDrop(add, ModRegistry.Blocks.TURTLE_NORMAL);
         computerDrop(add, ModRegistry.Blocks.TURTLE_ADVANCED);
 
+        blockDrop(add, ModRegistry.Blocks.LECTERN, LootItem.lootTableItem(Items.LECTERN), ExplosionCondition.survivesExplosion());
+
         add.accept(ModRegistry.Blocks.CABLE.get().getLootTable(), LootTable
             .lootTable()
             .withPool(LootPool.lootPool()

projects/common/src/main/java/dan200/computercraft/data/TagProvider.java

@@ -102,8 +102,14 @@ class TagProvider {
             ModRegistry.Items.MONITOR_ADVANCED.get()
         );
 
+        // Allow printed books to be placed in bookshelves.
         tags.tag(ItemTags.BOOKSHELF_BOOKS).add(ModRegistry.Items.PRINTED_BOOK.get());
 
+        // Allow any printout to be placed on lecterns. See also PrintoutItem and CustomLecternBlock.
+        tags.tag(ItemTags.LECTERN_BOOKS).add(
+            ModRegistry.Items.PRINTED_PAGE.get(), ModRegistry.Items.PRINTED_PAGES.get(), ModRegistry.Items.PRINTED_BOOK.get()
+        );
+
         tags.tag(ComputerCraftTags.Items.TURTLE_CAN_PLACE)
             .add(Items.GLASS_BOTTLE)
             .addTag(ItemTags.BOATS);

projects/common/src/main/java/dan200/computercraft/shared/ModRegistry.java

@@ -40,6 +40,8 @@ import dan200.computercraft.shared.data.PlayerCreativeLootCondition;
 import dan200.computercraft.shared.details.BlockDetails;
 import dan200.computercraft.shared.details.ItemDetails;
 import dan200.computercraft.shared.integration.PermissionRegistry;
+import dan200.computercraft.shared.lectern.CustomLecternBlock;
+import dan200.computercraft.shared.lectern.CustomLecternBlockEntity;
 import dan200.computercraft.shared.media.PrintoutMenu;
 import dan200.computercraft.shared.media.items.DiskItem;
 import dan200.computercraft.shared.media.items.PrintoutItem;
@@ -100,10 +102,12 @@ import net.minecraft.world.item.crafting.CustomRecipe;
 import net.minecraft.world.item.crafting.RecipeSerializer;
 import net.minecraft.world.item.crafting.SimpleCraftingRecipeSerializer;
 import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.SoundType;
 import net.minecraft.world.level.block.entity.BlockEntity;
 import net.minecraft.world.level.block.entity.BlockEntityType;
 import net.minecraft.world.level.block.state.BlockBehaviour;
 import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.NoteBlockInstrument;
 import net.minecraft.world.level.material.MapColor;
 import net.minecraft.world.level.storage.loot.predicates.LootItemConditionType;
 
@@ -171,6 +175,10 @@ public final class ModRegistry {
         public static final RegistryEntry<WiredModemFullBlock> WIRED_MODEM_FULL = REGISTRY.register("wired_modem_full",
             () -> new WiredModemFullBlock(modemProperties().mapColor(MapColor.STONE)));
         public static final RegistryEntry<CableBlock> CABLE = REGISTRY.register("cable", () -> new CableBlock(modemProperties().mapColor(MapColor.STONE)));
+
+        public static final RegistryEntry<CustomLecternBlock> LECTERN = REGISTRY.register("lectern", () -> new CustomLecternBlock(
+            BlockBehaviour.Properties.of().mapColor(MapColor.WOOD).instrument(NoteBlockInstrument.BASS).strength(2.5F).sound(SoundType.WOOD).ignitedByLava()
+        ));
     }
 
     public static class BlockEntities {
@@ -212,6 +220,8 @@ public final class ModRegistry {
             ofBlock(Blocks.WIRELESS_MODEM_NORMAL, (p, s) -> new WirelessModemBlockEntity(BlockEntities.WIRELESS_MODEM_NORMAL.get(), p, s, false));
         public static final RegistryEntry<BlockEntityType<WirelessModemBlockEntity>> WIRELESS_MODEM_ADVANCED =
             ofBlock(Blocks.WIRELESS_MODEM_ADVANCED, (p, s) -> new WirelessModemBlockEntity(BlockEntities.WIRELESS_MODEM_ADVANCED.get(), p, s, true));
+
+        public static final RegistryEntry<BlockEntityType<CustomLecternBlockEntity>> LECTERN = ofBlock(Blocks.LECTERN, CustomLecternBlockEntity::new);
     }
 
     public static final class Items {

projects/common/src/main/java/dan200/computercraft/shared/container/BasicContainer.java

@@ -4,16 +4,17 @@
 
 package dan200.computercraft.shared.container;
 
-import net.minecraft.core.NonNullList;
 import net.minecraft.world.Container;
 import net.minecraft.world.ContainerHelper;
 import net.minecraft.world.item.ItemStack;
 
+import java.util.List;
+
 /**
  * A basic implementation of {@link Container} which operates on a {@linkplain #getContents() list of stacks}.
  */
 public interface BasicContainer extends Container {
-    NonNullList<ItemStack> getContents();
+    List<ItemStack> getContents();
 
     @Override
     default int getContainerSize() {

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

@@ -0,0 +1,142 @@
+// SPDX-FileCopyrightText: 2024 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package dan200.computercraft.shared.lectern;
+
+import dan200.computercraft.shared.ModRegistry;
+import dan200.computercraft.shared.media.items.PrintoutItem;
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.stats.Stats;
+import net.minecraft.util.RandomSource;
+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.ItemStack;
+import net.minecraft.world.item.Items;
+import net.minecraft.world.item.context.UseOnContext;
+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.state.BlockState;
+import net.minecraft.world.phys.BlockHitResult;
+
+/**
+ * Extends {@link LecternBlock} with support for {@linkplain PrintoutItem printouts}.
+ * <p>
+ * Unlike the vanilla lectern, this block is never empty. If the book is removed from the lectern, it converts back to
+ * its vanilla version (see {@link #clearLectern(Level, BlockPos, BlockState)}).
+ *
+ * @see PrintoutItem#useOn(UseOnContext) Placing books into a lectern.
+ */
+public class CustomLecternBlock extends LecternBlock {
+    public CustomLecternBlock(Properties properties) {
+        super(properties);
+        registerDefaultState(defaultBlockState().setValue(HAS_BOOK, true));
+    }
+
+    /**
+     * Replace a vanilla lectern with a custom one.
+     *
+     * @param level      The current level.
+     * @param pos        The position of the lectern.
+     * @param blockState The current state of the lectern.
+     * @param item       The item to place in the custom lectern.
+     */
+    public static void replaceLectern(Level level, BlockPos pos, BlockState blockState, ItemStack item) {
+        level.setBlockAndUpdate(pos, ModRegistry.Blocks.LECTERN.get().defaultBlockState()
+            .setValue(HAS_BOOK, true)
+            .setValue(FACING, blockState.getValue(FACING))
+            .setValue(POWERED, blockState.getValue(POWERED)));
+
+        if (level.getBlockEntity(pos) instanceof CustomLecternBlockEntity be) be.setItem(item.split(1));
+    }
+
+    /**
+     * Remove a custom lectern and replace it with an empty vanilla one.
+     *
+     * @param level      The current level.
+     * @param pos        The position of the lectern.
+     * @param blockState The current state of the lectern.
+     */
+    static void clearLectern(Level level, BlockPos pos, BlockState blockState) {
+        level.setBlockAndUpdate(pos, Blocks.LECTERN.defaultBlockState()
+            .setValue(HAS_BOOK, false)
+            .setValue(FACING, blockState.getValue(FACING))
+            .setValue(POWERED, blockState.getValue(POWERED)));
+    }
+
+    @Override
+    @Deprecated
+    public ItemStack getCloneItemStack(BlockGetter level, BlockPos pos, BlockState state) {
+        return new ItemStack(Items.LECTERN);
+    }
+
+    @Override
+    public void tick(BlockState state, ServerLevel level, BlockPos pos, RandomSource random) {
+        // If we've no lectern, remove it.
+        if (level.getBlockEntity(pos) instanceof CustomLecternBlockEntity lectern && lectern.getItem().isEmpty()) {
+            clearLectern(level, pos, state);
+            return;
+        }
+
+        super.tick(state, level, pos, random);
+    }
+
+    @Override
+    public void onRemove(BlockState state, Level level, BlockPos pos, BlockState newState, boolean isMoving) {
+        if (state.is(newState.getBlock())) return;
+
+        if (level.getBlockEntity(pos) instanceof CustomLecternBlockEntity lectern) {
+            dropItem(level, pos, state, lectern.getItem().copy());
+        }
+
+        super.onRemove(state, level, pos, newState, isMoving);
+    }
+
+    private static void dropItem(Level level, BlockPos pos, BlockState state, ItemStack stack) {
+        if (stack.isEmpty()) return;
+
+        var direction = state.getValue(FACING);
+        var dx = 0.25 * direction.getStepX();
+        var dz = 0.25 * direction.getStepZ();
+        var entity = new ItemEntity(level, pos.getX() + 0.5 + dx, pos.getY() + 1, pos.getZ() + 0.5 + dz, stack);
+        entity.setDefaultPickUpDelay();
+        level.addFreshEntity(entity);
+    }
+
+    @Override
+    public String getDescriptionId() {
+        return Blocks.LECTERN.getDescriptionId();
+    }
+
+    @Override
+    public CustomLecternBlockEntity newBlockEntity(BlockPos pos, BlockState state) {
+        return new CustomLecternBlockEntity(pos, state);
+    }
+
+    @Override
+    public int getAnalogOutputSignal(BlockState blockState, Level level, BlockPos pos) {
+        return level.getBlockEntity(pos) instanceof CustomLecternBlockEntity lectern ? lectern.getRedstoneSignal() : 0;
+    }
+
+    @Override
+    public InteractionResult use(BlockState state, Level level, BlockPos pos, Player player, InteractionHand hand, BlockHitResult hit) {
+        if (!level.isClientSide && level.getBlockEntity(pos) instanceof CustomLecternBlockEntity lectern) {
+            if (player.isSecondaryUseActive()) {
+                // When shift+clicked with an empty hand, drop the item and replace with the normal lectern.
+                clearLectern(level, pos, state);
+            } else {
+                // Otherwise open the screen.
+                player.openMenu(lectern);
+            }
+
+            player.awardStat(Stats.INTERACT_WITH_LECTERN);
+        }
+
+        return InteractionResult.sidedSuccess(level.isClientSide);
+    }
+}

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

@@ -0,0 +1,193 @@
+// SPDX-FileCopyrightText: 2024 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package dan200.computercraft.shared.lectern;
+
+import dan200.computercraft.shared.ModRegistry;
+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.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.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;
+
+/**
+ * The block entity for our {@link CustomLecternBlock}.
+ *
+ * @see LecternBlockEntity
+ */
+public final class CustomLecternBlockEntity extends BlockEntity implements MenuProvider {
+    private static final String NBT_ITEM = "Item";
+    private static final String NBT_PAGE = "Page";
+
+    private ItemStack item = ItemStack.EMPTY;
+    private int page, pageCount;
+
+    public CustomLecternBlockEntity(BlockPos pos, BlockState blockState) {
+        super(ModRegistry.BlockEntities.LECTERN.get(), pos, blockState);
+    }
+
+    public ItemStack getItem() {
+        return item;
+    }
+
+    void setItem(ItemStack item) {
+        this.item = item;
+        itemChanged();
+        BlockEntityHelpers.updateBlock(this);
+    }
+
+    int getRedstoneSignal() {
+        if (item.getItem() instanceof PrintoutItem) {
+            var progress = pageCount > 1 ? (float) page / (pageCount - 1) : 1F;
+            return Mth.floor(progress * 14f) + 1;
+        }
+
+        return 15;
+    }
+
+    /**
+     * Called after the item has changed. This sets up the state for the new item.
+     */
+    private void itemChanged() {
+        if (item.getItem() instanceof PrintoutItem) {
+            pageCount = PrintoutItem.getPageCount(item);
+            page = Mth.clamp(page, 0, pageCount - 1);
+        } else {
+            pageCount = page = 0;
+        }
+    }
+
+    /**
+     * Set the current page, emitting a redstone pulse if needed.
+     *
+     * @param page The new page.
+     */
+    private void setPage(int page) {
+        if (this.page == page) return;
+
+        this.page = page;
+        setChanged();
+        if (getLevel() != null) LecternBlock.signalPageChange(getLevel(), getBlockPos(), getBlockState());
+    }
+
+    @Override
+    public void load(CompoundTag tag) {
+        super.load(tag);
+
+        item = tag.contains(NBT_ITEM, Tag.TAG_COMPOUND) ? ItemStack.of(tag.getCompound(NBT_ITEM)) : ItemStack.EMPTY;
+        page = tag.getInt(NBT_PAGE);
+        itemChanged();
+    }
+
+    @Override
+    protected void saveAdditional(CompoundTag tag) {
+        super.saveAdditional(tag);
+
+        if (!item.isEmpty()) tag.put(NBT_ITEM, item.save(new CompoundTag()));
+        if (item.getItem() instanceof PrintoutItem) tag.putInt(NBT_PAGE, page);
+    }
+
+    @Override
+    public Packet<ClientGamePacketListener> getUpdatePacket() {
+        return ClientboundBlockEntityDataPacket.create(this);
+    }
+
+    @Override
+    public CompoundTag getUpdateTag() {
+        var tag = super.getUpdateTag();
+        tag.put(NBT_ITEM, item.save(new CompoundTag()));
+        return tag;
+    }
+
+    @Nullable
+    @Override
+    public AbstractContainerMenu createMenu(int containerId, Inventory playerInventory, Player player) {
+        var item = getItem();
+        if (item.getItem() instanceof PrintoutItem) {
+            return new PrintoutMenu(
+                containerId, new LecternContainer(), 0,
+                p -> Container.stillValidBlockEntity(this, player, Container.DEFAULT_DISTANCE_LIMIT),
+                new PrintoutContainerData()
+            );
+        }
+
+        return null;
+    }
+
+    @Override
+    public Component getDisplayName() {
+        return getItem().getDisplayName();
+    }
+
+    /**
+     * A read-only container storing the lectern's contents.
+     */
+    private final class LecternContainer implements BasicContainer {
+        private final List<ItemStack> itemView = new AbstractList<>() {
+            @Override
+            public ItemStack get(int index) {
+                if (index != 0) throw new IndexOutOfBoundsException("Inventory only has one slot");
+                return item;
+            }
+
+            @Override
+            public int size() {
+                return 1;
+            }
+        };
+
+        @Override
+        public List<ItemStack> getContents() {
+            return itemView;
+        }
+
+        @Override
+        public void setChanged() {
+            // Should never happen, so a no-op.
+        }
+
+        @Override
+        public boolean stillValid(Player player) {
+            return !isRemoved();
+        }
+    }
+
+    /**
+     * {@link ContainerData} for a {@link PrintoutMenu}. This provides a read/write view of the current page.
+     */
+    private final class PrintoutContainerData implements SingleContainerData {
+        @Override
+        public int get() {
+            return page;
+        }
+
+        @Override
+        public void set(int index, int value) {
+            if (index == 0) setPage(value);
+        }
+    }
+}

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

@@ -6,6 +6,7 @@ package dan200.computercraft.shared.media.items;
 
 import com.google.common.base.Strings;
 import dan200.computercraft.shared.ModRegistry;
+import dan200.computercraft.shared.lectern.CustomLecternBlock;
 import dan200.computercraft.shared.media.PrintoutMenu;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.InteractionHand;
@@ -16,7 +17,10 @@ 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 net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.LecternBlock;
 
 import javax.annotation.Nullable;
 import java.util.List;
@@ -50,6 +54,22 @@ public class PrintoutItem extends Item {
         if (title != null && !title.isEmpty()) list.add(Component.literal(title));
     }
 
+    @Override
+    public InteractionResult useOn(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;
+        }
+    }
+
     @Override
     public InteractionResultHolder<ItemStack> use(Level world, Player player, InteractionHand hand) {
         var stack = player.getItemInHand(hand);

projects/common/src/main/resources/assets/computercraft/textures/entity/printout.png.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2024 The CC: Tweaked Developers
+
+SPDX-License-Identifier: MPL-2.0

projects/fabric/src/generated/resources/data/minecraft/tags/items/lectern_books.json

@@ -0,0 +1,4 @@
+{
+  "replace": false,
+  "values": ["computercraft:printed_page", "computercraft:printed_pages", "computercraft:printed_book"]
+}

projects/forge/src/generated/resources/data/minecraft/tags/items/lectern_books.json

@@ -0,0 +1 @@
+{"values": ["computercraft:printed_page", "computercraft:printed_pages", "computercraft:printed_book"]}