Add getters to masonry widget contexts (#735)

This fixes #728.

And update `flex` and `grid` examples to use them.
This allows external crates to access these fields for custom widgets.

Author: viktorstrate

masonry/src/contexts.rs

@@ -10,12 +10,14 @@ use dpi::LogicalPosition;
 use parley::{FontContext, LayoutContext};
 use tracing::{trace, warn};
 use vello::kurbo::Vec2;
+use vello::peniko::Color;
 use winit::window::ResizeDirection;
 
 use crate::action::Action;
 use crate::passes::layout::run_layout_on;
 use crate::render_root::{MutateCallback, RenderRootSignal, RenderRootState};
 use crate::text::TextBrush;
+use crate::theme::get_debug_color;
 use crate::tree_arena::{ArenaMutChildren, ArenaRefChildren};
 use crate::widget::{WidgetMut, WidgetRef, WidgetState};
 use crate::{AllowRawMut, BoxConstraints, Insets, Point, Rect, Size, Widget, WidgetId, WidgetPod};
@@ -226,6 +228,11 @@ impl_context_method!(
             self.widget_state.layout_rect()
         }
 
+        /// The offset of the baseline relative to the bottom of the widget.
+        pub fn baseline_offset(&self) -> f64 {
+            self.widget_state.baseline_offset
+        }
+
         /// The origin of the widget in window coordinates, relative to the top left corner of the
         /// content area.
         pub fn window_origin(&self) -> Point {
@@ -1123,6 +1130,29 @@ impl_context_method!(LayoutCtx<'_>, PaintCtx<'_>, {
     }
 });
 
+impl PaintCtx<'_> {
+    /// Whether debug paint is enabled.
+    ///
+    /// If this property is set, your widget may draw additional debug information
+    /// (such as the position of the text baseline).
+    /// These should normally use the [debug color][Self::debug_color] for this widget.
+    /// Please note that when debug painting is enabled, each widget's layout boundaries are
+    /// outlined by Masonry, so you should avoid duplicating that.
+    ///
+    /// Debug paint can be enabled by setting the environment variable `MASONRY_DEBUG_PAINT`.
+    pub fn debug_paint_enabled(&self) -> bool {
+        self.debug_paint
+    }
+
+    /// A color used for debug painting in this widget.
+    ///
+    /// This is normally used to paint additional debugging information
+    /// when debug paint is enabled, see [`Self::debug_paint_enabled`].
+    pub fn debug_color(&self) -> Color {
+        get_debug_color(self.widget_id().to_raw())
+    }
+}
+
 // --- MARK: RAW WRAPPERS ---
 macro_rules! impl_get_raw {
     ($SomeCtx:tt) => {

masonry/src/theme.rs

@@ -79,6 +79,10 @@ static DEBUG_COLOR: &[Color] = &[
     Color::rgb8(0, 0, 0),
 ];
 
+/// A color used for debug painting.
+///
+/// The same color is always returned given the same id, usually the id of a widget.
+/// When painting a widget, [`PaintCtx::debug_color`][crate::contexts::PaintCtx::debug_color] is typically used instead.
 pub fn get_debug_color(id: u64) -> Color {
     let color_num = id as usize % DEBUG_COLOR.len();
     DEBUG_COLOR[color_num]

masonry/src/widget/flex.rs

@@ -10,7 +10,6 @@ use vello::kurbo::common::FloatExt;
 use vello::kurbo::{Affine, Line, Stroke, Vec2};
 use vello::Scene;
 
-use crate::theme::get_debug_color;
 use crate::widget::WidgetMut;
 use crate::{
     AccessCtx, AccessEvent, BoxConstraints, EventCtx, LayoutCtx, PaintCtx, Point, PointerEvent,
@@ -1178,9 +1177,9 @@ impl Widget for Flex {
 
     fn paint(&mut self, ctx: &mut PaintCtx, scene: &mut Scene) {
         // paint the baseline if we're debugging layout
-        if ctx.debug_paint && ctx.widget_state.baseline_offset != 0.0 {
-            let color = get_debug_color(ctx.widget_id().to_raw());
-            let my_baseline = ctx.size().height - ctx.widget_state.baseline_offset;
+        if ctx.debug_paint_enabled() && ctx.baseline_offset() != 0.0 {
+            let color = ctx.debug_color();
+            let my_baseline = ctx.size().height - ctx.baseline_offset();
             let line = Line::new((0.0, my_baseline), (ctx.size().width, my_baseline));
 
             let stroke_style = Stroke::new(1.0).with_dashes(0., [4.0, 4.0]);

masonry/src/widget/grid.rs

@@ -7,7 +7,6 @@ use tracing::{trace_span, Span};
 use vello::kurbo::{Affine, Line, Stroke};
 use vello::Scene;
 
-use crate::theme::get_debug_color;
 use crate::widget::WidgetMut;
 use crate::{
     AccessCtx, AccessEvent, BoxConstraints, EventCtx, LayoutCtx, PaintCtx, Point, PointerEvent,
@@ -287,9 +286,9 @@ impl Widget for Grid {
 
     fn paint(&mut self, ctx: &mut PaintCtx, scene: &mut Scene) {
         // paint the baseline if we're debugging layout
-        if ctx.debug_paint && ctx.widget_state.baseline_offset != 0.0 {
-            let color = get_debug_color(ctx.widget_id().to_raw());
-            let my_baseline = ctx.size().height - ctx.widget_state.baseline_offset;
+        if ctx.debug_paint_enabled() && ctx.baseline_offset() != 0.0 {
+            let color = ctx.debug_color();
+            let my_baseline = ctx.size().height - ctx.baseline_offset();
             let line = Line::new((0.0, my_baseline), (ctx.size().width, my_baseline));
 
             let stroke_style = Stroke::new(1.0).with_dashes(0., [4.0, 4.0]);