Modding Horizon

Camera and collision reads

ClientHost::is_paused() reads the applied client pause state, not whether a pause screen is open. A multiplayer game continues running while its pause screen is open. The pause-change pre hook sees the old state; the post hook sees the new state.

ClientHost::playing() is true while the player is in the world with nothing over it: no screen, title, sign editor or book, so keys and zoom apply. ClientHost::mapping(name) reads a vanilla key mapping (key.forward, key.left, key.back, key.right, key.jump, key.sneak, key.sprint, key.attack, key.use) as a KeyMapping: whether it is held (KeyMapping.isDown) and the label of the key it is bound to, as Controls shows it. It is None for any other name. Both read without &mut, so the HUD and screen hooks can ask them.

ClientHost::clipboard_text() reads the system clipboard (KeyboardHandler.getClipboard, empty text when it holds none) and ClientHost::set_clipboard_text(text) writes it (setClipboard; empty text copies nothing). Both work only while the game handles a key, mouse or typed-text event, from the window or from the control socket (horizon-ctl key, mouse, type and its clicks): a key, mouse or screen hook that fires inside one, such as Ctrl+V into a mod's own field. At any other moment (a tick, a frame, a packet) the read is None and the write is false with nothing copied, so no mod reaches the clipboard without the player doing something. Both are None and false on a server, and take &self, so a screen hook can call them. Vanilla's KeyboardHandler has no such rule: Horizon adds it.

The camera() helper returns the most recently extracted world frame's camera, or none before one exists. Its position, interpolated eye height, partial tick, angles, final FOV, near/far planes and dimension accompany column-major view and projection matrices. The view is camera-relative and includes bob and spin; projection uses reversed Z. Earlier callbacks in a frame can see the previous frame. block_collision(pos) returns block-local [min_x, min_y, min_z, max_x, max_y, max_z] boxes with an empty collision context; unloaded blocks and collision errors give no boxes.

ClientHost::set_camera_type(type) is a queued client-only effect and takes &self, so shared callbacks such as camera_pose can request a perspective. camera_type() reports the latest request immediately; several requests coalesce to the last one. Requests before or during camera_pose apply before that frame's final camera, FOV and spectator post effects. The pose hook runs only once: its explicit position or angle overrides survive a refreshed vanilla camera. Requests from later render callbacks apply at the next frame's extraction. Setting a type never emits camera_type_cycle; F5 alone cycles, and its final event choice wins over requests made inside the cycle callback.

ClientHost::crosshair_target() returns the ordinary interaction-range target as CrosshairTarget::Block { pos, state, hit } or CrosshairTarget::Entity { entity, point }. The block hit contains its world-space location, face and inside flag; the entity point is also in world coordinates. It uses the game's current targeting ray and block/entity reach, respects blocks occluding entities, and returns None on a miss or without a client world. It can be read with a screen open. entity is an EntityRef carrying the current client level's epoch and network entity ID, including dragon parts. It becomes stale when the client level is replaced or the client disconnects; a same-level respawn keeps its epoch. This supplies identity, not client entity reads: the server-only entity data methods still reject client handles. Unlike view_hit and raycast, this does not find blocks in distant terrain or return a block behind a targeted entity.

Combat targeting

ClientHost::targeting() and set_targeting(ClientTargeting) control liquid picking, entity occlusion and an optional crosshair entity override. Defaults preserve ordinary vanilla targeting. Set pick_liquids to include source and flowing fluid shapes, or hit_through_walls to ignore block occlusion for entity picks and attacks. An entity override must name a live entity in this client level; stale or self handles make the setter return false without changing the controls. The setter requires a logged-in client world. An override is rechecked for reach, held-item range and occlusion when used and disappears from reads after its level is replaced.

Reach remains attribute-backed: use the server player's living handle and set_attribute_base(host, "minecraft:block_interaction_range", value) or "minecraft:entity_interaction_range". The client's cached reach follows the server's attribute updates. Client targeting controls do not grant extra server reach.

client_attack_target receives a mutable targets list before an ordinary melee click (spear jabs use their existing path). It starts with the crosshair entity. Replace it for redirection, append for multiple hits, or clear it to suppress an entity attack. Flow::Cancel cancels the batch. There is no batch cap; duplicates are sent once in first-occurrence order. Each target is checked again against live handles, attackability, reach, held-item range and the occlusion control. Clearing an entity hit does not mine the block behind it; an empty list on a block or miss keeps the ordinary path. Each accepted hit uses normal attack packets and prediction. Server validation and cooldowns still apply. Native and Wasm mods use the same typed API.