cranpose_foundation/
bring_into_view_spec.rs

1/// Where a scroll container puts a child that asks to be seen, such as a
2/// control that takes focus. Compose's `BringIntoViewSpec`, which a
3/// container reads from `local_bring_into_view_spec()`.
4#[derive(Clone, Copy, Debug, Default, PartialEq)]
5pub enum BringIntoViewSpec {
6    /// Scrolls as little as shows the child, and not at all while the child
7    /// is in view or larger than the container. Compose's default spec.
8    #[default]
9    Default,
10    /// Puts the child's leading edge at a fixed place in the container on
11    /// every request, so focus stays at one place while the content moves.
12    /// A child that would not fit after that place ends at the container's
13    /// end instead. Compose's pivot spec on a TV is
14    /// `Pivot { parent_fraction: 0.3, child_fraction: 0.0 }`.
15    Pivot {
16        /// The place, as a fraction of the container's size.
17        parent_fraction: f32,
18        /// How far the child sits before that place, as a fraction of the
19        /// child's size: 0.5 centers it on the place.
20        child_fraction: f32,
21    },
22}
23
24impl BringIntoViewSpec {
25    /// How far the container scrolls to put a child where this spec wants
26    /// it. The child starts `offset` past the container's leading edge and
27    /// is `size` long; the container is `container_size` long. A positive
28    /// answer moves the content toward the leading edge. Compose's
29    /// `calculateScrollDistance`.
30    pub fn calculate_scroll_distance(self, offset: f32, size: f32, container_size: f32) -> f32 {
31        match self {
32            Self::Default => {
33                let trailing = offset + size;
34                if (offset >= 0.0 && trailing <= container_size)
35                    || (offset < 0.0 && trailing > container_size)
36                {
37                    0.0
38                } else if offset.abs() < (trailing - container_size).abs() {
39                    offset
40                } else {
41                    trailing - container_size
42                }
43            }
44            Self::Pivot {
45                parent_fraction,
46                child_fraction,
47            } => {
48                let pivot = parent_fraction * container_size - child_fraction * size;
49                let target = if size <= container_size && container_size - pivot < size {
50                    container_size - size
51                } else {
52                    pivot
53                };
54                offset - target
55            }
56        }
57    }
58}
cranpose_foundation/bring_into_view_spec.rs

cranpose_foundation/
bring_into_view_spec.rs
