terminal/new: scrolling viewport

src/terminal/Terminal.zig

@@ -2747,6 +2747,7 @@ test "Terminal: disabled wraparound with wide grapheme and half space" {
     }
 }
 
+// X
 test "Terminal: print writes to bottom if scrolled" {
     var t = try init(testing.allocator, 5, 2);
     defer t.deinit(testing.allocator);

src/terminal/new/Screen.zig

@@ -214,6 +214,25 @@ pub fn cursorDownScroll(self: *Screen) !void {
     self.cursor.page_cell = page_rac.cell;
 }
 
+/// Options for scrolling the viewport of the terminal grid. The reason
+/// we have this in addition to PageList.Scroll is because we have additional
+/// scroll behaviors that are not part of the PageList.Scroll enum.
+pub const Scroll = union(enum) {
+    /// For all of these, see PageList.Scroll.
+    active,
+    top,
+    delta_row: isize,
+};
+
+/// Scroll the viewport of the terminal grid.
+pub fn scroll(self: *Screen, behavior: Scroll) void {
+    switch (behavior) {
+        .active => self.pages.scroll(.{ .active = {} }),
+        .top => self.pages.scroll(.{ .top = {} }),
+        .delta_row => |v| self.pages.scroll(.{ .delta_row = v }),
+    }
+}
+
 /// Dump the screen to a string. The writer given should be buffered;
 /// this function does not attempt to efficiently write and generally writes
 /// one byte at a time.

src/terminal/new/Terminal.zig

@@ -1394,6 +1394,43 @@ test "Terminal: overwrite grapheme should clear grapheme data" {
     }
 }
 
+test "Terminal: print writes to bottom if scrolled" {
+    var t = try init(testing.allocator, 5, 2);
+    defer t.deinit(testing.allocator);
+
+    // Basic grid writing
+    for ("hello") |c| try t.print(c);
+    t.setCursorPos(0, 0);
+
+    // Make newlines so we create scrollback
+    // 3 pushes hello off the screen
+    try t.index();
+    try t.index();
+    try t.index();
+    {
+        const str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("", str);
+    }
+
+    // Scroll to the top
+    t.screen.scroll(.{ .top = {} });
+    {
+        const str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("hello", str);
+    }
+
+    // Type
+    try t.print('A');
+    t.screen.scroll(.{ .active = {} });
+    {
+        const str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("\nA", str);
+    }
+}
+
 test "Terminal: soft wrap" {
     var t = try init(testing.allocator, 3, 80);
     defer t.deinit(testing.allocator);