From a2161586dab6837d8c641b6f93ad476f861d8580 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, 5 Nov 2019 03:33:24 +0100
Subject: [PATCH] Implement state-less scrolling in `TextInput`

---
 wgpu/src/renderer/text_input.rs | 121 +++++++++++++++++---------------
 1 file changed, 65 insertions(+), 56 deletions(-)

diff --git a/wgpu/src/renderer/text_input.rs b/wgpu/src/renderer/text_input.rs
index 95ea964e61..cff8bf236a 100644
--- a/wgpu/src/renderer/text_input.rs
+++ b/wgpu/src/renderer/text_input.rs
@@ -87,70 +87,79 @@ impl text_input::Renderer for Renderer {
             vertical_alignment: VerticalAlignment::Center,
         };
 
-        let content = Primitive::Clip {
-            bounds: text_bounds,
-            offset: Vector::new(0, 0),
-            content: Box::new(if text_input.state.is_focused {
-                use wgpu_glyph::{GlyphCruncher, Scale, Section};
-
-                let text_before_cursor = &text_input
-                    .value
-                    .until(text_input.state.cursor_position(&text_input.value))
-                    .to_string();
-
-                let mut text_value_width = self
-                    .glyph_brush
-                    .borrow_mut()
-                    .glyph_bounds(Section {
-                        text: text_before_cursor,
-                        bounds: (f32::INFINITY, text_bounds.height),
-                        scale: Scale { x: size, y: size },
-                        ..Default::default()
-                    })
-                    .map(|bounds| bounds.width().round())
-                    .unwrap_or(0.0);
-
-                let spaces_at_the_end = text_before_cursor.len()
-                    - text_before_cursor.trim_end().len();
-
-                if spaces_at_the_end > 0 {
-                    let space_width = {
-                        let glyph_brush = self.glyph_brush.borrow();
-
-                        // TODO: Select appropriate font
-                        let font = &glyph_brush.fonts()[0];
-
-                        font.glyph(' ')
-                            .scaled(Scale { x: size, y: size })
-                            .h_metrics()
-                            .advance_width
-                    };
-
-                    text_value_width += spaces_at_the_end as f32 * space_width;
-                }
-
-                let cursor = Primitive::Quad {
-                    bounds: Rectangle {
-                        x: text_bounds.x + text_value_width,
-                        y: text_bounds.y,
-                        width: 1.0,
-                        height: text_bounds.height,
-                    },
-                    background: Background::Color(Color::BLACK),
-                    border_radius: 0,
+        let (contents_primitive, offset) = if text_input.state.is_focused {
+            use wgpu_glyph::{GlyphCruncher, Scale, Section};
+
+            let text_before_cursor = &text_input
+                .value
+                .until(text_input.state.cursor_position(&text_input.value))
+                .to_string();
+
+            let mut text_value_width = self
+                .glyph_brush
+                .borrow_mut()
+                .glyph_bounds(Section {
+                    text: text_before_cursor,
+                    bounds: (f32::INFINITY, text_bounds.height),
+                    scale: Scale { x: size, y: size },
+                    ..Default::default()
+                })
+                .map(|bounds| bounds.width().round())
+                .unwrap_or(0.0);
+
+            let spaces_at_the_end =
+                text_before_cursor.len() - text_before_cursor.trim_end().len();
+
+            if spaces_at_the_end > 0 {
+                let space_width = {
+                    let glyph_brush = self.glyph_brush.borrow();
+
+                    // TODO: Select appropriate font
+                    let font = &glyph_brush.fonts()[0];
+
+                    font.glyph(' ')
+                        .scaled(Scale { x: size, y: size })
+                        .h_metrics()
+                        .advance_width
                 };
 
+                text_value_width += spaces_at_the_end as f32 * space_width;
+            }
+
+            let cursor = Primitive::Quad {
+                bounds: Rectangle {
+                    x: text_bounds.x + text_value_width,
+                    y: text_bounds.y,
+                    width: 1.0,
+                    height: text_bounds.height,
+                },
+                background: Background::Color(Color::BLACK),
+                border_radius: 0,
+            };
+
+            (
                 Primitive::Group {
                     primitives: vec![value, cursor],
-                }
-            } else {
-                value
-            }),
+                },
+                Vector::new(
+                    ((text_value_width + 5.0) - text_bounds.width).max(0.0)
+                        as u32,
+                    0,
+                ),
+            )
+        } else {
+            (value, Vector::new(0, 0))
+        };
+
+        let contents = Primitive::Clip {
+            bounds: text_bounds,
+            offset,
+            content: Box::new(contents_primitive),
         };
 
         (
             Primitive::Group {
-                primitives: vec![border, input, content],
+                primitives: vec![border, input, contents],
             },
             if is_mouse_over {
                 MouseCursor::Text