From 5f56b96dd2b1f9b730a86f7c84c1bb8f135afb98 Mon Sep 17 00:00:00 2001
From: Wez Furlong <wez@wezfurlong.org>
Date: Tue, 31 May 2022 21:49:12 -0700
Subject: [PATCH] background: allow repeat to mirror

---
 config/src/background.rs                 |  4 ++++
 wezterm-gui/src/quad.rs                  | 16 ++++++++++++----
 wezterm-gui/src/termwindow/background.rs | 24 ++++++++++++++++++++----
 3 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/config/src/background.rs b/config/src/background.rs
index 78a564dc4..26ae676c2 100644
--- a/config/src/background.rs
+++ b/config/src/background.rs
@@ -222,6 +222,10 @@ pub enum BackgroundRepeat {
     /// Repeat as much as possible to cover the area.
     /// The last image will be clipped if it doesn't fit.
     Repeat,
+    /// Like Repeat, except that the image is alternately
+    /// mirrored. Helpful when the image doesn't seamlessly
+    /// tile.
+    Mirror,
     /*
     /// Repeat as much as possible without clipping.
     /// The first and last images are aligned with the edges,
diff --git a/wezterm-gui/src/quad.rs b/wezterm-gui/src/quad.rs
index 53802bb8d..87f76a3bc 100644
--- a/wezterm-gui/src/quad.rs
+++ b/wezterm-gui/src/quad.rs
@@ -45,10 +45,18 @@ pub struct Quad<'a> {
 impl<'a> Quad<'a> {
     /// Assign the texture coordinates
     pub fn set_texture(&mut self, coords: TextureRect) {
-        self.vert[V_TOP_LEFT].tex = (coords.min_x(), coords.min_y());
-        self.vert[V_TOP_RIGHT].tex = (coords.max_x(), coords.min_y());
-        self.vert[V_BOT_LEFT].tex = (coords.min_x(), coords.max_y());
-        self.vert[V_BOT_RIGHT].tex = (coords.max_x(), coords.max_y());
+        let x1 = coords.min_x();
+        let x2 = coords.max_x();
+        let y1 = coords.min_y();
+        let y2 = coords.max_y();
+        self.set_texture_discrete(x1, x2, y1, y2);
+    }
+
+    pub fn set_texture_discrete(&mut self, x1: f32, x2: f32, y1: f32, y2: f32) {
+        self.vert[V_TOP_LEFT].tex = (x1, y1);
+        self.vert[V_TOP_RIGHT].tex = (x2, y1);
+        self.vert[V_BOT_LEFT].tex = (x1, y2);
+        self.vert[V_BOT_RIGHT].tex = (x2, y2);
     }
 
     /// Set the color glyph "flag"
diff --git a/wezterm-gui/src/termwindow/background.rs b/wezterm-gui/src/termwindow/background.rs
index 413664177..c2c448ed8 100644
--- a/wezterm-gui/src/termwindow/background.rs
+++ b/wezterm-gui/src/termwindow/background.rs
@@ -465,19 +465,22 @@ impl crate::TermWindow {
             .unwrap_or(height);
 
         // log::info!("computed {width}x{height}");
+
+        let mut start_tile = 0;
         if let Some(factor) = layer.def.attachment.scroll_factor() {
             let distance = top as f32 * self.render_metrics.cell_size.height as f32 * factor;
             let num_tiles = distance / repeat_y;
             origin_y -= num_tiles.fract() * repeat_y;
+            start_tile = num_tiles.floor() as usize;
         }
 
         let limit_y = top_pixel + pixel_height;
 
-        for y_step in 0.. {
-            let offset_y = y_step as f32 * repeat_y;
+        for y_step in start_tile.. {
+            let offset_y = (y_step - start_tile) as f32 * repeat_y;
             let origin_y = origin_y + offset_y;
             if origin_y >= limit_y
-                || (y_step > 0 && layer.def.repeat_y == BackgroundRepeat::NoRepeat)
+                || (y_step > start_tile && layer.def.repeat_y == BackgroundRepeat::NoRepeat)
             {
                 break;
             }
@@ -493,7 +496,20 @@ impl crate::TermWindow {
                 let mut quad = layer0.allocate()?;
                 // log::info!("quad {origin_x},{origin_y} {width}x{height}");
                 quad.set_position(origin_x, origin_y, origin_x + width, origin_y + height);
-                quad.set_texture(sprite.texture_coords());
+
+                let coords = sprite.texture_coords();
+                let mut x1 = coords.min_x();
+                let mut x2 = coords.max_x();
+                let mut y1 = coords.min_y();
+                let mut y2 = coords.max_y();
+                if layer.def.repeat_x == BackgroundRepeat::Mirror && x_step % 2 == 1 {
+                    std::mem::swap(&mut x1, &mut x2);
+                }
+                if layer.def.repeat_y == BackgroundRepeat::Mirror && y_step % 2 == 1 {
+                    std::mem::swap(&mut y1, &mut y2);
+                }
+
+                quad.set_texture_discrete(x1, x2, y1, y2);
                 quad.set_is_background_image();
                 quad.set_hsv(Some(layer.def.hsb));
                 quad.set_fg_color(color);