sx/library/modules/ui/layout.sx

#import "modules/std.sx";
#import "modules/math";
#import "modules/ui/types.sx";
#import "modules/ui/view.sx";

// VStack layout: measure all children, stack vertically
// Width is constrained from parent; height is unspecified (children choose)
layout_vstack :: (children: *List(ViewChild), bounds: Frame, spacing: f32, alignment: HAlignment) {
    n := children.len;
    if n == 0 { return; }

    content_width := bounds.size.width;

    y := bounds.origin.y;
    i := 0;
    while i < n {
        child := @children.items[i];
        child_size := child.view.size_that_fits(ProposedSize.{
            width = content_width,
            height = null
        });
        x_offset := align_h(alignment, child_size.width, content_width);
        child.computed_frame = Frame.{
            origin = Point.{ x = bounds.origin.x + x_offset, y = y },
            size = child_size
        };
        child.view.layout(child.computed_frame);
        y = y + child_size.height + spacing;
        i += 1;
    }
}

// HStack layout: measure all children, stack horizontally
// Height is constrained from parent; width is unspecified (children choose)
layout_hstack :: (children: *List(ViewChild), bounds: Frame, spacing: f32, alignment: VAlignment) {
    n := children.len;
    if n == 0 { return; }

    content_height := bounds.size.height;

    x := bounds.origin.x;
    i := 0;
    while i < n {
        child := @children.items[i];
        child_size := child.view.size_that_fits(ProposedSize.{
            width = null,
            height = content_height
        });
        y_offset := align_v(alignment, child_size.height, content_height);
        child.computed_frame = Frame.{
            origin = Point.{ x = x, y = bounds.origin.y + y_offset },
            size = child_size
        };
        child.view.layout(child.computed_frame);
        x = x + child_size.width + spacing;
        i += 1;
    }
}

// ZStack layout: all children get same bounds, aligned
layout_zstack :: (children: *List(ViewChild), bounds: Frame, alignment: Alignment) {
    n := children.len;
    if n == 0 { return; }

    proposal := ProposedSize.{
        width = bounds.size.width,
        height = bounds.size.height
    };

    i := 0;
    while i < n {
        child := @children.items[i];
        child_size := child.view.size_that_fits(proposal);
        x_offset := align_h(alignment.h, child_size.width, bounds.size.width);
        y_offset := align_v(alignment.v, child_size.height, bounds.size.height);
        child.computed_frame = Frame.{
            origin = Point.{ x = bounds.origin.x + x_offset, y = bounds.origin.y + y_offset },
            size = child_size
        };
        child.view.layout(child.computed_frame);
        i += 1;
    }
}

// Measure helpers — compute stack size from children

measure_vstack :: (children: *List(ViewChild), proposal: ProposedSize, spacing: f32) -> Size {
    n := children.len;
    if n == 0 { return Size.zero(); }

    max_width : f32 = 0.0;
    total_height : f32 = 0.0;

    // Measure children: constrain width, leave height unspecified
    child_proposal := ProposedSize.{ width = proposal.width, height = null };
    i := 0;
    while i < n {
        child_size := children.items[i].view.size_that_fits(child_proposal);
        children.items[i].computed_frame.size = child_size;
        if child_size.width > max_width { max_width = child_size.width; }
        total_height = total_height + child_size.height;
        i += 1;
    }

    total_height = total_height + spacing * xx (n - 1);

    result_width := min(proposal.width ?? max_width, max_width);
    Size.{ width = result_width, height = total_height }
}

measure_hstack :: (children: *List(ViewChild), proposal: ProposedSize, spacing: f32) -> Size {
    n := children.len;
    if n == 0 { return Size.zero(); }

    total_width : f32 = 0.0;
    max_height : f32 = 0.0;

    // Measure children: constrain height, leave width unspecified
    child_proposal := ProposedSize.{ width = null, height = proposal.height };
    i := 0;
    while i < n {
        child_size := children.items[i].view.size_that_fits(child_proposal);
        children.items[i].computed_frame.size = child_size;
        total_width = total_width + child_size.width;
        if child_size.height > max_height { max_height = child_size.height; }
        i += 1;
    }

    total_width = total_width + spacing * xx (n - 1);

    result_height := min(proposal.height ?? max_height, max_height);
    Size.{ width = total_width, height = result_height }
}

measure_zstack :: (children: *List(ViewChild), proposal: ProposedSize) -> Size {
    n := children.len;
    if n == 0 { return Size.zero(); }

    max_width : f32 = 0.0;
    max_height : f32 = 0.0;

    i := 0;
    while i < n {
        child_size := children.items[i].view.size_that_fits(proposal);
        children.items[i].computed_frame.size = child_size;
        if child_size.width > max_width { max_width = child_size.width; }
        if child_size.height > max_height { max_height = child_size.height; }
        i += 1;
    }

    Size.{ width = max_width, height = max_height }
}