Implement faux scrolling

This patch implements faux scrolling inside the alternate screen buffer.

Whenever the user scrolls up or down while the alternate screen buffer
is active, instead of actual scrolling three up/down arrow keys are
inserted.

2 files changed, 48 insertions, 22 deletions

diff --git a/src/input.rs b/src/input.rs
index 4901a409..8f6048f0 100644
--- a/src/input.rs
+++ b/src/input.rs
@@ -365,7 +365,7 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
     }
 
     pub fn on_mouse_wheel(&mut self, delta: MouseScrollDelta, phase: TouchPhase) {
-        let modes = mode::MOUSE_REPORT_CLICK | mode::MOUSE_MOTION | mode::SGR_MOUSE;
+        let modes = mode::MOUSE_REPORT_CLICK | mode::MOUSE_MOTION | mode::SGR_MOUSE | mode::ALT_SCREEN_BUF;
         if !self.ctx.terminal_mode().intersects(modes) {
             return;
         }
@@ -374,6 +374,18 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
             MouseScrollDelta::LineDelta(_columns, lines) => {
                 let to_scroll = self.ctx.mouse_mut().lines_scrolled + lines;
 
+                // Faux scrolling
+                if self.ctx.terminal_mode().intersects(mode::ALT_SCREEN_BUF) {
+                    if to_scroll > 0. {
+                        // Scroll up three lines
+                        self.ctx.write_to_pty("\x1bOA\x1bOA\x1bOA".as_bytes());
+                    } else {
+                        // Scroll down three lines
+                        self.ctx.write_to_pty("\x1bOB\x1bOB\x1bOB".as_bytes());
+                    }
+                    return;
+                }
+
                 let code = if to_scroll > 0.0 {
                     64
                 } else {
@@ -396,15 +408,26 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
                         let height = self.ctx.size_info().cell_height as i32;
 
                         while self.ctx.mouse_mut().scroll_px.abs() >= height {
-                            let button = if self.ctx.mouse_mut().scroll_px > 0 {
-                                self.ctx.mouse_mut().scroll_px -= height;
-                                64
+                            if self.ctx.terminal_mode().intersects(mode::ALT_SCREEN_BUF) {
+                                // Faux scrolling
+                                if self.ctx.mouse_mut().scroll_px > 0 {
+                                    // Scroll up three lines
+                                    self.ctx.write_to_pty("\x1bOA\x1bOA\x1bOA".as_bytes());
+                                } else {
+                                    // Scroll down three lines
+                                    self.ctx.write_to_pty("\x1bOB\x1bOB\x1bOB".as_bytes());
+                                }
                             } else {
-                                self.ctx.mouse_mut().scroll_px += height;
-                                65
-                            };
-
-                            self.normal_mouse_report(button);
+                                let button = if self.ctx.mouse_mut().scroll_px > 0 {
+                                    self.ctx.mouse_mut().scroll_px -= height;
+                                    64
+                                } else {
+                                    self.ctx.mouse_mut().scroll_px += height;
+                                    65
+                                };
+
+                                self.normal_mouse_report(button);
+                            }
                         }
                     },
                     _ => (),
diff --git a/src/term/mod.rs b/src/term/mod.rs
index 6bce8451..c5933236 100644
--- a/src/term/mod.rs
+++ b/src/term/mod.rs
@@ -416,19 +416,20 @@ impl<'a> Iterator for RenderableCellsIter<'a> {
 pub mod mode {
     bitflags! {
         pub struct TermMode: u16 {
-            const SHOW_CURSOR         = 0b000000000001;
-            const APP_CURSOR          = 0b000000000010;
-            const APP_KEYPAD          = 0b000000000100;
-            const MOUSE_REPORT_CLICK  = 0b000000001000;
-            const BRACKETED_PASTE     = 0b000000010000;
-            const SGR_MOUSE           = 0b000000100000;
-            const MOUSE_MOTION        = 0b000001000000;
-            const LINE_WRAP           = 0b000010000000;
-            const LINE_FEED_NEW_LINE  = 0b000100000000;
-            const ORIGIN              = 0b001000000000;
-            const INSERT              = 0b010000000000;
-            const FOCUS_IN_OUT        = 0b100000000000;
-            const ANY                 = 0b111111111111;
+            const SHOW_CURSOR         = 0b0000000000001;
+            const APP_CURSOR          = 0b0000000000010;
+            const APP_KEYPAD          = 0b0000000000100;
+            const MOUSE_REPORT_CLICK  = 0b0000000001000;
+            const BRACKETED_PASTE     = 0b0000000010000;
+            const SGR_MOUSE           = 0b0000000100000;
+            const MOUSE_MOTION        = 0b0000001000000;
+            const LINE_WRAP           = 0b0000010000000;
+            const LINE_FEED_NEW_LINE  = 0b0000100000000;
+            const ORIGIN              = 0b0001000000000;
+            const INSERT              = 0b0010000000000;
+            const FOCUS_IN_OUT        = 0b0100000000000;
+            const ALT_SCREEN_BUF      = 0b1000000000000;
+            const ANY                 = 0b1111111111111;
             const NONE                = 0;
         }
     }
@@ -1789,6 +1790,7 @@ impl ansi::Handler for Term {
         trace!("set_mode: {:?}", mode);
         match mode {
             ansi::Mode::SwapScreenAndSetRestoreCursor => {
+                self.mode.insert(mode::ALT_SCREEN_BUF);
                 self.save_cursor_position();
                 if !self.alt {
                     self.swap_alt();
@@ -1818,6 +1820,7 @@ impl ansi::Handler for Term {
         trace!("unset_mode: {:?}", mode);
         match mode {
             ansi::Mode::SwapScreenAndSetRestoreCursor => {
+                self.mode.remove(mode::ALT_SCREEN_BUF);
                 self.restore_cursor_position();
                 if self.alt {
                     self.swap_alt();