This is the 1.15+ version of this tutorial. For the 1.14 version, see Rendering blocks and items dynamically using block entity renderers (1.14).

Make sure you added a block entity before reading this tutorial!

Blocks by themselves aren't that interesting, they just stay static at a certain location and a certain size until broken. We can use block entity renderers to render items and blocks associated with a block entity far more dynamically - render multiple different items, at differing locations and sizes, and more.

In this tutorial we'll build off the block entity we created by adding a BlockEntityRenderer to it. The renderer will display a jukebox floating above the block, going up and down and spinning.

The first thing we need to do is create our BlockEntityRenderer class:

@Environment(EnvType.CLIENT)
public class DemoBlockEntityRenderer implements BlockEntityRenderer<DemoBlockEntity > {
    // A jukebox itemstack
    private static final ItemStack stack = new ItemStack(Items.JUKEBOX);
 
    public DemoBlockEntityRenderer(BlockEntityRendererFactory.Context ctx) {}
 
    @Override
    public void render(DemoBlockEntity blockEntity, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, int overlay) {
    }
}

We're going to need to register our BlockEntityRenderer, but only for the client. This wouldn't matter in a single-player setting, since the server runs in the same process as the client. However, in a multiplayer setting, where the server runs in a different process than the client, the server code has no concept of a “BlockEntityRenderer”, and as a result would not accept registering one. To run initialization code only for the client, we need to setup a client entrypoint.

In the entrypoint that implements ClientModInitializer:

@Environment(EnvType.CLIENT)
public class ExampleModClient implements ClientModInitializer {
    @Override
    public void onInitializeClient() {
        // Here we will put client-only registration code
    }
}

Set this class as the client entrypoint in your fabric.mod.json, if you haven't done yet (modify the path as needed):

"fabric.mod.json"

{
  [...]
  "entrypoints": {
    [...]
    "client": [
      {
        "value": "net.fabricmc.example.ExampleModClient"
      }
    ]
  },
  [...]
}    

And register the BlockEntityRenderer in our ClientModInitializer:

    @Override
    public void onInitializeClient() {
        BlockEntityRendererFactories.register(DEMO_BLOCK_ENTITY, DemoBlockEntityRenderer::new);
    }

We override the render method which gets called every frame(!), and in it we will do our rendering - for starters, call matrices.push(); which is mandatory when doing GL calls (we will doing those right after):

    public void render(DemoBlockEntity blockEntity, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, int overlay) {
       matrices.push();
    }

We then perform the movement of the jukebox (matrices.translate) and rotation (matrices.multiply). There are two parts to the translation: we translate it to 0.5, 1.25, and 0.5 which is above the center of our block. The second part is the part that changes: the offset in the y value. The offset is the height of the item for any given frame. We recalculate this each time because we want it to be animating bouncing up and down. We calculate this by:

• Getting the current world time, which changes over time.
• Adding the partial ticks. (The partial ticks is a fractional value representing the amount of time that’s passed between the last full tick and now. We use this because otherwise the animation would be jittery because there are fewer ticks per second than frames per second.)
• Dividing that by 8 to slow the movement down.
• Taking the sine of that to produce a value that ranges between -1 and 1, like a sine wave.
• Dividing that by 4 to compress the sine wave vertically so the item doesn’t move up and down as much.

    public void render(DemoBlockEntity blockEntity, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, int overlay) {
        [...]
        // Calculate the current offset in the y value
        double offset = Math.sin((blockEntity.getWorld().getTime() + tickDelta) / 8.0) / 4.0;
        // Move the item
        matrices.translate(0.5, 1.25 + offset, 0.5);
 
        // Rotate the item
        matrices.multiply(RotationAxis.POSITIVE_Y.rotationDegrees((blockEntity.getWorld().getTime() + tickDelta) * 4));
    }

Finally, we will get the Minecraft 'ItemRenderer' and render the jukebox item by using renderItem. We also pass ModelTransformationMode.GROUND¹⁾ to renderItem because we want a similiar effect to an item lying on the ground. Try experimenting with this value and see what happens (it's an enum). We also need to call matrices.pop(); after these GL calls:

    public void render(DemoBlockEntity blockEntity, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, int overlay) {
        [...]
        MinecraftClient.getInstance().getItemRenderer().renderItem(stack, ModelTransformationMode.GROUND, light, overlay, matrices, vertexConsumers, blockEntity.getWorld(), 0);
 
        // Mandatory call after GL calls
        matrices.pop();
    }

You can try your newly created block entity renderer right now. However, if you didn't make your block transparent, you will notice something is amiss - the floating block, the jukebox, is pitch black! This is because by default, whatever you render in the block entity, will receive light as if it's in the same position as the block entity. So the floating block receives light from inside our opaque block, which means it receives no light! To fix this, we will tell Minecraft to receive light from one block above the location of the block entity.

To get the light, we call WorldRenderer#getLightmapCoordinates() on the position above our block entity, and to use the light we use it in renderItem():

    @Override
    public void render(DemoBlockEntity blockEntity, float tickDelta, MatrixStack matrices, VertexConsumerProvider vertexConsumers, int light, int overlay) {
        [...]
 
        int lightAbove = WorldRenderer.getLightmapCoordinates(blockEntity.getWorld(), blockEntity.getPos().up());
        MinecraftClient.getInstance().getItemRenderer().renderItem(stack, ModelTransformationMode.GROUND, lightAbove, OverlayTexture.DEFAULT_UV, matrices, vertexConsumers, blockEntity.getWorld(), 0);
 
        [...]
    }

The jukebox should now have the proper lighting.

Sometimes you want to render according to the block entity data (nbt), and you find they are all empty, even if you can access the data through /data get block command. That's because you did not sync data from server to client. See Sync data from server to client.