From fb1deaabe55f83eed81fd89eca7fe739bebefa3c Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Thu, 7 Mar 2024 14:29:20 +0100
Subject: [PATCH] Render tree of Widgets as RgbImage

---
 showbits-common/src/lib.rs    |  3 +-
 showbits-common/src/rect.rs   |  6 +--
 showbits-common/src/render.rs | 79 +++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 4 deletions(-)
 create mode 100644 showbits-common/src/render.rs

diff --git a/showbits-common/src/lib.rs b/showbits-common/src/lib.rs
index fefc724..7cca6f2 100644
--- a/showbits-common/src/lib.rs
+++ b/showbits-common/src/lib.rs
@@ -1,7 +1,8 @@
-pub use crate::{node::*, rect::*, vec2::*, view::*, widget::*};
+pub use crate::{node::*, rect::*, render::*, vec2::*, view::*, widget::*};
 
 mod node;
 mod rect;
+mod render;
 mod vec2;
 mod view;
 mod widget;
diff --git a/showbits-common/src/rect.rs b/showbits-common/src/rect.rs
index 798bfa0..5d29d4f 100644
--- a/showbits-common/src/rect.rs
+++ b/showbits-common/src/rect.rs
@@ -56,19 +56,19 @@ impl Rect {
     }
 
     /// Construct a rectangle from its north-east corner and size.
-    pub fn from_corner_ne(ne: Vec2, size: Vec2) -> Self {
+    pub fn from_ne(ne: Vec2, size: Vec2) -> Self {
         let sw = ne + (size - 1).neg_x();
         Self::from_ne_sw(ne, sw)
     }
 
     /// Construct a rectangle from its south-west corner and size.
-    pub fn from_corner_sw(sw: Vec2, size: Vec2) -> Self {
+    pub fn from_sw(sw: Vec2, size: Vec2) -> Self {
         let ne = sw + (size - 1).neg_y();
         Self::from_ne_sw(ne, sw)
     }
 
     /// Construct a rectangle from its south-east corner and size.
-    pub fn from_corner_se(se: Vec2, size: Vec2) -> Self {
+    pub fn from_se(se: Vec2, size: Vec2) -> Self {
         let nw = se - (size - 1);
         Self::from_nw_se(nw, se)
     }
diff --git a/showbits-common/src/render.rs b/showbits-common/src/render.rs
new file mode 100644
index 0000000..af30def
--- /dev/null
+++ b/showbits-common/src/render.rs
@@ -0,0 +1,79 @@
+use image::RgbImage;
+use taffy::{AvailableSpace, NodeId, Point, Size, TaffyResult, TaffyTree};
+
+use crate::{Rect, Vec2, View, Widget};
+
+fn point_to_vec2(point: Point<f32>) -> Vec2 {
+    Vec2::new(point.x as i32, point.y as i32)
+}
+
+fn size_to_vec2(size: Size<f32>) -> Vec2 {
+    Vec2::new(size.width as i32, size.height as i32)
+}
+
+fn layout(
+    tree: &mut TaffyTree<Box<dyn Widget>>,
+    root: NodeId,
+    available: Size<AvailableSpace>,
+) -> TaffyResult<()> {
+    tree.enable_rounding(); // Just to make sure
+    tree.compute_layout_with_measure(root, available, |known, available, _node, context| {
+        if let Some(widget) = context {
+            widget.size(known, available)
+        } else {
+            Size::ZERO
+        }
+    })
+}
+
+fn render_to_view(
+    tree: &mut TaffyTree<Box<dyn Widget>>,
+    node: NodeId,
+    view: &mut View<'_>,
+) -> anyhow::Result<()> {
+    let layout = tree.layout(node)?;
+    let area = Rect::from_nw(point_to_vec2(layout.location), size_to_vec2(layout.size));
+    let mut view = view.dup().zoom(area);
+
+    // First pass
+    if let Some(ctx) = tree.get_node_context_mut(node) {
+        ctx.draw_below(&mut view)?;
+    }
+
+    // Render children
+    let mut children = vec![];
+    for child in tree.children(node)? {
+        let order = tree.layout(child)?.order;
+        children.push((order, child));
+    }
+    children.sort_unstable_by_key(|(order, _)| *order);
+    for (_, child) in children {
+        render_to_view(tree, child, &mut view)?;
+    }
+
+    // Second pass
+    if let Some(ctx) = tree.get_node_context_mut(node) {
+        ctx.draw_above(&mut view)?;
+    }
+
+    Ok(())
+}
+
+pub fn render(
+    tree: &mut TaffyTree<Box<dyn Widget>>,
+    root: NodeId,
+    available: Size<AvailableSpace>,
+) -> anyhow::Result<RgbImage> {
+    layout(tree, root, available)?;
+
+    let layout = tree.layout(root)?;
+    assert_eq!(layout.location.x, 0.0);
+    assert_eq!(layout.location.y, 0.0);
+    // TODO Check how taffy treats the border?
+
+    let (width, height) = size_to_vec2(layout.size).to_u32();
+    let mut image = RgbImage::new(width, height);
+    render_to_view(tree, root, &mut View::new(&mut image))?;
+
+    Ok(image)
+}