Client basics

You use the client API through mod.client() in the client entrypoint (ClientModInitializer). Calling it on a dedicated server gives POLY-CLIENT-001.

ClientRegistrar client = mod.client();
KeyBinding open = client.keyBinding("open", KeyCodes.K);
client.hudLayer("status", canvas -> canvas.drawText("Hi", 4, 4, 0xFFFFFFFF));
mod.events().register(ClientEvents.TICK, view -> {
    if (open.consumeClick()) {
        view.showActionBar("Open!");
    }
});

Key bindings

Declare one with keyBinding(path, KeyCodes.K).

• It appears in the controls settings, and the player can rebind it.
• The name is key.<mod>.<path> in the lang file, and the category name is key.category.<mod>.keybinds.
• consumeClick() consumes the number of presses one at a time. isDown() tells whether the key is held down now.
• KeyCodes has letter keys, F6–F10, UNBOUND, and others.
• If adding fails, you get POLY-CLIENT-004.

HUD layers

hudLayer(path, canvas -> …) is called on the render thread every frame.

HudCanvas	Meaning
width(), height()	Screen size (GUI coordinates)
textWidth(text)	Text width
drawText(text, x, y, argb)	Text
fill(x1, y1, x2, y2, argb)	Rectangle
drawTexture(texture, x, y, width, height)	Texture (for example, a dynamic texture)

client.hudLayer("status", canvas -> {
    String text = "Native Showcase";
    canvas.fill(2, 2, 6 + canvas.textWidth(text), 14, 0x80000000);
    canvas.drawText(text, 4, 4, 0xFFFFD54F);
});

If an exception occurs, Poly Mod Loader turns off only that layer and logs POLY-CLIENT-003. It is called every frame, so keep it light.

ClientView

Client events (TICK, JOINED_WORLD, LEFT_WORLD) give you a ClientView.

Method	Meaning
player(), world()	The current player and world (Optional, empty outside a world)
showActionBar(text)	Action bar message
openScreen(screen), closeScreen(), isScreenOpen()	Mod screens
cameraPerspective(), setCameraPerspective(p)	Camera perspective
setPostEffect(id), clearPostEffect(), postEffect()	Post-processing shader
leaveWorld()	Same as "Save and Quit to Title"

mod.events().register(ClientEvents.JOINED_WORLD, view -> LOGGER.info("joined"));   // LEFT_WORLD exists too

The list of client events is in Events.

Error codes

Code	Meaning
POLY-CLIENT-001	Client API used on a server
POLY-CLIENT-002	Client ID error or registration closed
POLY-CLIENT-003	HUD layer or drawing failed (only that layer is turned off)
POLY-CLIENT-004	Adding a key binding failed
POLY-CLIENT-005	A dynamic texture was uploaded from a thread other than the client thread, or particle or post-processing hookup failed
POLY-CLIENT-006	A mod shader pipeline could not be created or compiled (logged once, that rectangle is skipped)
POLY-CLIENT-007	A mod shader uniform value threw an exception or has the wrong count, or the upload failed (logged once, the last valid value is used)