support DECSET/DECRST (CSI ? Pm h) to change where the cursor ends up

after printing a sixel image. The default is for the cursor to be
moved to the first column of the line after the image. When we receive
CSI ? 8452 h, we will instead leave the cursor on the last line of the
image, on the next column past the end of the image.

3 files changed, 20 insertions, 5 deletions

diff --git a/alacritty_terminal/src/ansi.rs b/alacritty_terminal/src/ansi.rs
index 14617de1..35763f92 100644
--- a/alacritty_terminal/src/ansi.rs
+++ b/alacritty_terminal/src/ansi.rs
@@ -569,6 +569,8 @@ pub enum Mode {
     SixelPrivateColorRegisters = 1070,
     /// ?2004
     BracketedPaste = 2004,
+    /// Sixel scrolling leaves cursor to right of graphic.
+    SixelCursorToTheRight = 8452,
 }
 
 impl Mode {
@@ -600,6 +602,7 @@ impl Mode {
                 1049 => Mode::SwapScreenAndSetRestoreCursor,
                 1070 => Mode::SixelPrivateColorRegisters,
                 2004 => Mode::BracketedPaste,
+                8452 => Mode::SixelCursorToTheRight,
                 _ => {
                     trace!("[unimplemented] primitive mode: {}", num);
                     return None;
diff --git a/alacritty_terminal/src/term/mod.rs b/alacritty_terminal/src/term/mod.rs
index 959f99ef..7849dd5e 100644
--- a/alacritty_terminal/src/term/mod.rs
+++ b/alacritty_terminal/src/term/mod.rs
@@ -46,7 +46,7 @@ const TITLE_STACK_MAX_DEPTH: usize = 4096;
 const INITIAL_TABSTOPS: usize = 8;
 
 bitflags! {
-    pub struct TermMode: u32 {
+    pub struct TermMode: u64 {
         const NONE                = 0;
         const SHOW_CURSOR         = 0b0000_0000_0000_0000_0001;
         const APP_CURSOR          = 0b0000_0000_0000_0000_0010;
@@ -69,7 +69,8 @@ bitflags! {
         const URGENCY_HINTS       = 0b0010_0000_0000_0000_0000;
         const SIXEL_SCROLLING     = 0b0100_0000_0000_0000_0000;
         const SIXEL_PRIV_PALETTE  = 0b1000_0000_0000_0000_0000;
-        const ANY                 = std::u32::MAX;
+        const SIXEL_CURSOR_TO_THE_RIGHT  = 0b0001_0000_0000_0000_0000_0000;
+        const ANY                 = std::u64::MAX;
     }
 }
 
@@ -1585,6 +1586,9 @@ impl<T: EventListener> Handler for Term<T> {
             ansi::Mode::SixelPrivateColorRegisters => {
                 self.mode.insert(TermMode::SIXEL_PRIV_PALETTE)
             },
+            ansi::Mode::SixelCursorToTheRight => {
+                self.mode.insert(TermMode::SIXEL_CURSOR_TO_THE_RIGHT);
+            },
         }
     }
 
@@ -1632,6 +1636,9 @@ impl<T: EventListener> Handler for Term<T> {
                 self.graphics.sixel_shared_palette = None;
                 self.mode.remove(TermMode::SIXEL_PRIV_PALETTE);
             },
+            ansi::Mode::SixelCursorToTheRight => {
+                self.mode.remove(TermMode::SIXEL_CURSOR_TO_THE_RIGHT)
+            },
         }
     }
 
@@ -1855,12 +1862,17 @@ impl<T: EventListener> Handler for Term<T> {
             let graphic_cell = GraphicCell { texture: texture.clone(), offset_x: 0, offset_y };
             self.grid[line][Column(left)].set_graphic(graphic_cell);
 
-            if scrolling {
+            if scrolling && offset_y < height - self.cell_height as u16 {
                 self.linefeed();
             }
         }
 
-        if scrolling {
+        if self.mode.contains(TermMode::SIXEL_CURSOR_TO_THE_RIGHT) {
+            let graphic_columns = (graphic.width + self.cell_width - 1) / self.cell_width;
+            let right = min(self.columns(), left + graphic_columns);
+            self.move_forward(Column(right));
+        } else if scrolling {
+            self.linefeed();
             self.carriage_return();
         }
     }
diff --git a/docs/escape_support.md b/docs/escape_support.md
index bc951753..4673cedc 100644
--- a/docs/escape_support.md
+++ b/docs/escape_support.md
@@ -57,7 +57,7 @@ brevity.
 | `CSI ? h`  | PARTIAL     | Supported modes:                                  |
 |            |             |   `1`, `3`, `6`, `7`, `12`, `25`, `1000`, `1002`  |
 |            |             |   `1004`, `1005`, `1006`, `1007`, `1042`, `1049`  |
-|            |             |   `2004`                                          |
+|            |             |   `2004`, `8452`                                  |
 | `CSI I`    | IMPLEMENTED |                                                   |
 | `CSI J`    | IMPLEMENTED |                                                   |
 | `CSI K`    | IMPLEMENTED |                                                   |