From 9cab88b986a168ad2aedba35ac000091b829e8a4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?=
 <hector0193@gmail.com>
Date: Tue, 18 Aug 2020 04:12:23 +0200
Subject: [PATCH] Draw only visible options in `overlay::Menu`

---
 graphics/src/overlay/menu.rs | 15 ++++++++++++---
 native/src/overlay/menu.rs   |  4 +++-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/graphics/src/overlay/menu.rs b/graphics/src/overlay/menu.rs
index a952f065..f42c5e3c 100644
--- a/graphics/src/overlay/menu.rs
+++ b/graphics/src/overlay/menu.rs
@@ -42,6 +42,7 @@ where
         &mut self,
         bounds: Rectangle,
         cursor_position: Point,
+        viewport: &Rectangle,
         options: &[T],
         hovered_option: Option<usize>,
         padding: u16,
@@ -52,16 +53,24 @@ where
         use std::f32;
 
         let is_mouse_over = bounds.contains(cursor_position);
+        let option_height = text_size as usize + padding as usize * 2;
 
         let mut primitives = Vec::new();
 
-        for (i, option) in options.iter().enumerate() {
+        let offset = viewport.y - bounds.y;
+        let start = (offset / option_height as f32) as usize;
+        let end =
+            ((offset + viewport.height) / option_height as f32).ceil() as usize;
+
+        let visible_options = &options[start..end.min(options.len())];
+
+        for (i, option) in visible_options.iter().enumerate() {
+            let i = start + i;
             let is_selected = hovered_option == Some(i);
 
             let bounds = Rectangle {
                 x: bounds.x,
-                y: bounds.y
-                    + ((text_size as usize + padding as usize * 2) * i) as f32,
+                y: bounds.y + (option_height * i) as f32,
                 width: bounds.width,
                 height: f32::from(text_size + padding * 2),
             };
diff --git a/native/src/overlay/menu.rs b/native/src/overlay/menu.rs
index 29e4e63d..4b392a8e 100644
--- a/native/src/overlay/menu.rs
+++ b/native/src/overlay/menu.rs
@@ -372,12 +372,13 @@ where
         _defaults: &Renderer::Defaults,
         layout: Layout<'_>,
         cursor_position: Point,
-        _viewport: &Rectangle,
+        viewport: &Rectangle,
     ) -> Renderer::Output {
         self::Renderer::draw(
             renderer,
             layout.bounds(),
             cursor_position,
+            viewport,
             self.options,
             *self.hovered_option,
             self.padding,
@@ -423,6 +424,7 @@ pub trait Renderer:
         &mut self,
         bounds: Rectangle,
         cursor_position: Point,
+        viewport: &Rectangle,
         options: &[T],
         hovered_option: Option<usize>,
         padding: u16,