1 files changed, 232 insertions, 0 deletions
diff --git a/azalea-physics/src/clip.rs b/azalea-physics/src/clip.rs
new file mode 100644
index 00000000..ca85c32a
--- /dev/null
+++ b/azalea-physics/src/clip.rs
@@ -0,0 +1,232 @@
+use azalea_block::BlockState;
+use azalea_core::{lerp, BlockHitResult, BlockPos, Direction, Vec3, EPSILON};
+use azalea_inventory::ItemSlot;
+use azalea_world::ChunkStorage;
+use bevy_ecs::entity::Entity;
+
+use crate::collision::{BlockWithShape, VoxelShape};
+
+#[derive(Debug, Clone)]
+pub struct ClipContext {
+    pub from: Vec3,
+    pub to: Vec3,
+    pub block_shape_type: BlockShapeType,
+    pub fluid_pick_type: FluidPickType,
+    // pub collision_context: EntityCollisionContext,
+}
+impl ClipContext {
+    // minecraft passes in the world and blockpos here... but it doesn't actually
+    // seem necessary?
+    pub fn block_shape(&self, block_state: BlockState) -> &VoxelShape {
+        // TODO: implement the other shape getters
+        // (see the ClipContext.Block class in the vanilla source)
+        match self.block_shape_type {
+            BlockShapeType::Collider => block_state.shape(),
+            BlockShapeType::Outline => block_state.shape(),
+            BlockShapeType::Visual => block_state.shape(),
+            BlockShapeType::FallDamageResetting => block_state.shape(),
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub enum BlockShapeType {
+    Collider,
+    Outline,
+    Visual,
+    FallDamageResetting,
+}
+#[derive(Debug, Copy, Clone)]
+pub enum FluidPickType {
+    None,
+    SourceOnly,
+    Any,
+    Water,
+}
+#[derive(Debug, Clone)]
+pub struct EntityCollisionContext {
+    pub descending: bool,
+    pub entity_bottom: f64,
+    pub held_item: ItemSlot,
+    // pub can_stand_on_fluid: Box<dyn Fn(&FluidState) -> bool>,
+    pub entity: Entity,
+}
+
+pub fn clip(chunk_storage: &ChunkStorage, context: ClipContext) -> BlockHitResult {
+    traverse_blocks(
+        context.from,
+        context.to,
+        context,
+        |context, block_pos| {
+            let block_state = chunk_storage.get_block_state(block_pos).unwrap_or_default();
+            // TODO: add fluid stuff to this (see getFluidState in vanilla source)
+            let block_shape = context.block_shape(block_state);
+            clip_with_interaction_override(
+                &context.from,
+                &context.to,
+                block_pos,
+                block_shape,
+                &block_state,
+            )
+            // let block_distance = if let Some(block_hit_result) =
+            // block_hit_result {     context.from.distance_to_sqr(&
+            // block_hit_result.location) } else {
+            //     f64::MAX
+            // };
+        },
+        |context| {
+            let vec = context.from - context.to;
+            BlockHitResult::miss(
+                context.to,
+                Direction::nearest(vec),
+                BlockPos::from(context.to),
+            )
+        },
+    )
+}
+
+// default BlockHitResult clipWithInteractionOverride(Vec3 world, Vec3 from,
+// BlockPos to, VoxelShape shape,     BlockState block) {
+//  BlockHitResult blockHitResult = shape.clip(world, from, to);
+//  if (blockHitResult != null) {
+//     BlockHitResult var7 = block.getInteractionShape(this, to).clip(world,
+// from, to);     if (var7 != null
+//           && var7.getLocation().subtract(world).lengthSqr() <
+// blockHitResult.getLocation().subtract(world).lengthSqr()) {        return
+// blockHitResult.withDirection(var7.getDirection());     }
+//  }
+
+//  return blockHitResult;
+// }
+fn clip_with_interaction_override(
+    from: &Vec3,
+    to: &Vec3,
+    block_pos: &BlockPos,
+    block_shape: &VoxelShape,
+    block_state: &BlockState,
+) -> Option<BlockHitResult> {
+    let block_hit_result = block_shape.clip(from, to, block_pos);
+    if let Some(block_hit_result) = block_hit_result {
+        // TODO: minecraft calls .getInteractionShape here
+        // are there even any blocks that have a physics shape different from the
+        // interaction shape???
+        // (if not then you can delete this comment)
+        // (if there are then you have to implement BlockState::interaction_shape, lol
+        // have fun)
+        let interaction_shape = block_state.shape();
+        let interaction_hit_result = interaction_shape.clip(from, to, block_pos);
+        if let Some(interaction_hit_result) = interaction_hit_result {
+            if interaction_hit_result.location.distance_to_sqr(from)
+                < block_hit_result.location.distance_to_sqr(from)
+            {
+                return Some(block_hit_result.with_direction(interaction_hit_result.direction));
+            }
+        }
+        Some(block_hit_result)
+    } else {
+        block_hit_result
+    }
+}
+
+pub fn traverse_blocks<C, T>(
+    from: Vec3,
+    to: Vec3,
+    context: C,
+    get_hit_result: impl Fn(&C, &BlockPos) -> Option<T>,
+    get_miss_result: impl Fn(&C) -> T,
+) -> T {
+    if from == to {
+        return get_miss_result(&context);
+    }
+
+    let right_after_end = Vec3 {
+        x: lerp(-EPSILON, to.x, from.x),
+        y: lerp(-EPSILON, to.y, from.y),
+        z: lerp(-EPSILON, to.z, from.z),
+    };
+
+    let right_before_start = Vec3 {
+        x: lerp(-EPSILON, from.x, to.x),
+        y: lerp(-EPSILON, from.y, to.y),
+        z: lerp(-EPSILON, from.z, to.z),
+    };
+
+    let mut current_block = BlockPos::from(right_before_start);
+    if let Some(data) = get_hit_result(&context, &current_block) {
+        return data;
+    }
+
+    let vec = right_after_end - right_before_start;
+
+    /// Returns either -1, 0, or 1, depending on whether the number is negative,
+    /// zero, or positive.
+    ///
+    /// This function exists because f64::signum doesn't check for 0.
+    fn get_number_sign(num: f64) -> f64 {
+        if num == 0. {
+            0.
+        } else {
+            num.signum()
+        }
+    }
+
+    let vec_sign = Vec3 {
+        x: get_number_sign(vec.x),
+        y: get_number_sign(vec.y),
+        z: get_number_sign(vec.z),
+    };
+
+    #[rustfmt::skip]
+    let percentage_step = Vec3 {
+        x: if vec_sign.x == 0. { f64::MAX } else { vec_sign.x / vec.x },
+        y: if vec_sign.y == 0. { f64::MAX } else { vec_sign.y / vec.y },
+        z: if vec_sign.z == 0. { f64::MAX } else { vec_sign.z / vec.z },
+    };
+
+    let mut percentage = Vec3 {
+        x: percentage_step.x
+            * if vec_sign.x > 0. {
+                1. - right_before_start.x.fract()
+            } else {
+                right_before_start.x.fract().abs()
+            },
+        y: percentage_step.y
+            * if vec_sign.y > 0. {
+                1. - right_before_start.y.fract()
+            } else {
+                right_before_start.y.fract().abs()
+            },
+        z: percentage_step.z
+            * if vec_sign.z > 0. {
+                1. - right_before_start.z.fract()
+            } else {
+                right_before_start.z.fract().abs()
+            },
+    };
+
+    loop {
+        if percentage.x > 1. && percentage.y > 1. && percentage.z > 1. {
+            return get_miss_result(&context);
+        }
+
+        if percentage.x < percentage.y {
+            if percentage.x < percentage.z {
+                current_block.x += vec_sign.x as i32;
+                percentage.x += percentage_step.x;
+            } else {
+                current_block.z += vec_sign.z as i32;
+                percentage.z += percentage_step.z;
+            }
+        } else if percentage.y < percentage.z {
+            current_block.y += vec_sign.y as i32;
+            percentage.y += percentage_step.y;
+        } else {
+            current_block.z += vec_sign.z as i32;
+            percentage.z += percentage_step.z;
+        }
+
+        if let Some(data) = get_hit_result(&context, &current_block) {
+            return data;
+        }
+    }
+}