typing jumps scroll to bottom

TODO.md

@@ -1,6 +1,8 @@
 Bugs:
 
 * Underline should use freetype underline thickness hint
+* Any printing action forces scroll to jump to bottom, this makes it impossible
+  to scroll up while logs are coming in or something
 
 Performance:
 

src/terminal/Screen.zig

@@ -121,6 +121,15 @@ pub fn deinit(self: *Screen, alloc: Allocator) void {
     self.* = undefined;
 }
 
+/// This returns true if the display area is anchored at the bottom currently.
+pub fn displayIsBottom(self: Screen) bool {
+    return self.visible_offset == self.bottomOffset();
+}
+
+fn bottomOffset(self: Screen) usize {
+    return self.bottom - self.rows;
+}
+
 /// Returns an iterator that can be used to iterate over all of the rows
 /// from index zero.
 pub fn rowIterator(self: *const Screen) RowIterator {
@@ -429,7 +438,12 @@ test "Screen: scrolling" {
     var s = try init(alloc, 3, 5, 0);
     defer s.deinit(alloc);
     s.testWriteString("1ABCD\n2EFGH\n3IJKL");
+
+    try testing.expect(s.displayIsBottom());
+
+    // Scroll down, should still be bottom
     s.scroll(.{ .delta = 1 });
+    try testing.expect(s.displayIsBottom());
 
     // Test our row index
     try testing.expectEqual(@as(usize, 5), s.rowIndex(0));
@@ -462,6 +476,7 @@ test "Screen: scroll down from 0" {
     defer s.deinit(alloc);
     s.testWriteString("1ABCD\n2EFGH\n3IJKL");
     s.scroll(.{ .delta = -1 });
+    try testing.expect(s.displayIsBottom());
 
     {
         // Test our contents rotated
@@ -494,6 +509,7 @@ test "Screen: scrollback" {
 
     // Scrolling to the bottom
     s.scroll(.{ .bottom = {} });
+    try testing.expect(s.displayIsBottom());
 
     {
         // Test our contents rotated
@@ -504,6 +520,7 @@ test "Screen: scrollback" {
 
     // Scrolling back should make it visible again
     s.scroll(.{ .delta = -1 });
+    try testing.expect(!s.displayIsBottom());
 
     {
         // Test our contents rotated

src/terminal/Terminal.zig

@@ -203,6 +203,9 @@ pub fn print(self: *Terminal, c: u21) !void {
     const tracy = trace(@src());
     defer tracy.end();
 
+    // If we're not at the bottom, then we need to move there
+    if (!self.screen.displayIsBottom()) self.screen.scroll(.{ .bottom = {} });
+
     // If we're soft-wrapping, then handle that first.
     if (self.cursor.pending_wrap and self.mode_autowrap) {
         // Mark that the cell is wrapped, which guarantees that there is
@@ -691,12 +694,15 @@ pub fn scrollDown(self: *Terminal, count: usize) void {
 
 /// Options for scrolling the viewport of the terminal grid.
 pub const ScrollViewport = union(enum) {
+    /// Scroll to the top of the scrollback
+    top: void,
     delta: isize,
 };
 
 /// Scroll the viewport of the terminal grid.
 pub fn scrollViewport(self: *Terminal, behavior: ScrollViewport) void {
     self.screen.scroll(switch (behavior) {
+        .top => .{ .top = {} },
         .delta => |delta| .{ .delta_no_grow = delta },
     });
 }
@@ -766,6 +772,41 @@ test "Terminal: soft wrap" {
     }
 }
 
+test "Terminal: print scrolls back to bottom" {
+    var t = try init(testing.allocator, 5, 2);
+    defer t.deinit(testing.allocator);
+
+    // Basic grid writing
+    for ("hello") |c| try t.print(c);
+
+    // Make newlines so we create scrollback
+    // 3 pushes hello off the screen
+    t.index();
+    t.index();
+    t.index();
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("", str);
+    }
+
+    // Scroll to the top
+    t.scrollViewport(.{ .top = {} });
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("hello", str);
+    }
+
+    // Type
+    try t.print('A');
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("\nA", str);
+    }
+}
+
 test "Terminal: linefeed and carriage return" {
     var t = try init(testing.allocator, 80, 80);
     defer t.deinit(testing.allocator);