correct shapes for blocks with random offsets

1 files changed, 79 insertions, 0 deletions

diff --git a/azalea-physics/src/collision/shape_offset.rs b/azalea-physics/src/collision/shape_offset.rs
new file mode 100644
index 00000000..2832d680
--- /dev/null
+++ b/azalea-physics/src/collision/shape_offset.rs
@@ -0,0 +1,79 @@
+use std::borrow::Cow;
+
+use azalea_block::BlockState;
+use azalea_core::{
+    math::get_seed,
+    position::{BlockPos, Vec3},
+};
+use azalea_registry::builtin::BlockKind;
+
+use crate::collision::{VoxelShape, blocks::RANDOM_SHAPE_OFFSETS_MAP};
+
+/// Adds the random offset for the shape, given the block state and position.
+///
+/// For most blocks, this won't have any effect. It's only used for a few blocks
+/// like flowers and bamboo.
+pub fn apply_shape_offset(
+    block: BlockState,
+    pos: BlockPos,
+    shape: &'static VoxelShape,
+) -> Cow<'static, VoxelShape> {
+    // don't waste time checking the block if it's already known to be empty. also,
+    // it's faster to compare addresses than to call `.is_empty`.
+    if std::ptr::eq(shape, &*super::EMPTY_SHAPE) {
+        return Cow::Borrowed(shape);
+    }
+
+    let offset_kind = RANDOM_SHAPE_OFFSETS_MAP[block.id() as usize];
+    if offset_kind == 0 {
+        return Cow::Borrowed(shape);
+    }
+
+    let kind = block.as_block_kind();
+
+    let mut max_horizontal_offset = 0.25;
+    // search `getMaxHorizontalOffset` in the vanilla code
+    // TODO: sulfur spike gets added here in 26.2
+    if kind == BlockKind::PointedDripstone {
+        max_horizontal_offset = 2. / 16.;
+    }
+
+    // these ids are required to be the same as the ones in shapes.py
+    let delta = match offset_kind {
+        // see offsetType in BlockBehaviour.java
+        1 => {
+            // xz
+            xyz_offset_for_pos(pos.with_y(0), max_horizontal_offset, 0.)
+        }
+        2 => {
+            // xyz
+
+            let mut max_vertical_offset = 0.2;
+            if kind == BlockKind::SmallDripleaf {
+                // search `getMaxVerticalOffset` in the vanilla code
+                max_vertical_offset = 0.1;
+            }
+
+            xyz_offset_for_pos(pos, max_horizontal_offset, max_vertical_offset)
+        }
+        _ => unreachable!(),
+    };
+
+    Cow::Owned(shape.move_relative(delta))
+}
+
+fn xyz_offset_for_pos(pos: BlockPos, max_horizontal_offset: f64, max_vertical_offset: f64) -> Vec3 {
+    let seed = get_seed(pos);
+    let y = if max_vertical_offset == 0. {
+        0.
+    } else {
+        ((((seed >> 4) & 15) as f32 / 15.) as f64 - 1.) * max_vertical_offset
+    };
+
+    let x = (((seed & 15) as f32 / 15.) as f64 - 0.5) * 0.5;
+    let x = x.clamp(-max_horizontal_offset, max_horizontal_offset);
+    let z = ((((seed >> 8) & 15) as f32 / 15.) as f64 - 0.5) * 0.5;
+    let z = z.clamp(-max_horizontal_offset, max_horizontal_offset);
+
+    Vec3 { x, y, z }
+}