terminal: add Screen.cursorScrollAbove and tests

src/terminal/Screen.zig

@@ -5,6 +5,7 @@ const Allocator = std.mem.Allocator;
 const assert = std.debug.assert;
 const ansi = @import("ansi.zig");
 const charsets = @import("charsets.zig");
+const fastmem = @import("../fastmem.zig");
 const kitty = @import("kitty.zig");
 const sgr = @import("sgr.zig");
 const unicode = @import("../unicode/main.zig");
@@ -741,6 +742,100 @@ pub fn cursorDownScroll(self: *Screen) !void {
     }
 }
 
+/// This scrolls the active area at and above the cursor. The lines below
+/// the cursor are not scrolled.
+pub fn cursorScrollAbove(self: *Screen) !void {
+    // If the cursor is on the bottom of the screen, its faster to use
+    // our specialized function for that case.
+    if (self.cursor.y == self.pages.rows - 1) {
+        return try self.cursorDownScroll();
+    }
+
+    defer self.assertIntegrity();
+
+    // Logic below assumes we always have at least one row that isn't moving
+    assert(self.cursor.y < self.pages.rows - 1);
+
+    const old_pin = self.cursor.page_pin.*;
+    if (try self.pages.grow()) |new_page_node| {
+        // We allocated a new page and went to it. In this case, our new
+        // empty line is at the top of this page.
+
+        // Prev is never null because pagelist asserts that we always have
+        // memory for at least two pages. This is an assertion.
+        assert(new_page_node.prev.? == old_pin.page);
+        const prev_page = &old_pin.page.data;
+        const new_page = &new_page_node.data;
+
+        const prev_rows = prev_page.rows.ptr(prev_page.memory.ptr);
+        const new_rows = new_page.rows.ptr(new_page.memory.ptr);
+        const prev_last_row = &prev_rows[prev_page.size.rows - 1];
+
+        // First, copy the last row of the previous page to the top
+        // of our current page.
+        try new_page.cloneRowFrom(
+            prev_page,
+            &new_rows[0],
+            prev_last_row,
+        );
+
+        // Update our cursor metadata now. We call methods below that assert
+        // integrity in debug modes so we want to put ourselves in a
+        // consistent state first.
+        self.cursor.page_pin.* = self.cursor.page_pin.down(1).?;
+        self.cursorChangePin(self.cursor.page_pin.*);
+        const page_rac = self.cursor.page_pin.rowAndCell();
+        self.cursor.page_row = page_rac.row;
+        self.cursor.page_cell = page_rac.cell;
+
+        // Third, clear the last row of the previous page.
+        self.clearCells(
+            prev_page,
+            prev_last_row,
+            prev_page.getCells(prev_last_row),
+        );
+        var dirty = prev_page.dirtyBitSet();
+        dirty.set(prev_page.size.rows - 1);
+    } else {
+        // In this case, it means grow() didn't allocate a new page. This
+        // allows us to perform a fast path by rotating rows on the same page.
+        assert(old_pin.page == self.cursor.page_pin.page);
+        self.cursor.page_pin.* = self.cursor.page_pin.down(1).?;
+
+        const pin = self.cursor.page_pin;
+        const page = &self.cursor.page_pin.page.data;
+
+        // Rotate the rows so that the newly created empty row is at the
+        // beginning. e.g. [ 0 1 2 3 ] in to [ 3 0 1 2 ].
+        var rows = page.rows.ptr(page.memory.ptr);
+        fastmem.rotateOnceR(Row, rows[pin.y..page.size.rows]);
+
+        // Mark all our rotated rows as dirty.
+        var dirty = page.dirtyBitSet();
+        dirty.setRangeValue(.{ .start = pin.y, .end = page.size.rows }, true);
+
+        // Setup our cursor caches after the rotation so it points to the
+        // correct data
+        const page_rac = self.cursor.page_pin.rowAndCell();
+        self.cursor.page_row = page_rac.row;
+        self.cursor.page_cell = page_rac.cell;
+
+        // Note: we don't need to call cursorChangePin here because
+        // the pin page is the same so there is no accounting to do for
+        // styles or any of that.
+    }
+
+    if (self.cursor.style_id != style.default_id) {
+        // The newly created line needs to be styled according to
+        // the bg color if it is set.
+        if (self.cursor.style.bgCell()) |blank_cell| {
+            const cell_current: [*]pagepkg.Cell = @ptrCast(self.cursor.page_cell);
+            const cells = cell_current - self.cursor.x;
+            @memset(cells[0..self.pages.cols], blank_cell);
+        }
+    }
+}
+
 /// Move the cursor down if we're not at the bottom of the screen. Otherwise
 /// scroll. Currently only used for testing.
 fn cursorDownOrScroll(self: *Screen) !void {
@@ -3817,6 +3912,125 @@ test "Screen: scroll and clear ignore blank lines" {
     }
 }
 
+test "Screen: scroll above same page" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var s = try init(alloc, 10, 3, 10);
+    defer s.deinit();
+    try s.setAttribute(.{ .direct_color_bg = .{ .r = 155 } });
+    try s.testWriteString("1ABCD\n2EFGH\n3IJKL");
+    s.cursorAbsolute(0, 1);
+    s.pages.clearDirty();
+    try s.cursorScrollAbove();
+
+    {
+        const contents = try s.dumpStringAlloc(alloc, .{ .viewport = .{} });
+        defer alloc.free(contents);
+        try testing.expectEqualStrings("2EFGH\n\n3IJKL", contents);
+    }
+    {
+        const list_cell = s.pages.getCell(.{ .active = .{ .x = 0, .y = 1 } }).?;
+        const cell = list_cell.cell;
+        try testing.expect(cell.content_tag == .bg_color_rgb);
+        try testing.expectEqual(Cell.RGB{
+            .r = 155,
+            .g = 0,
+            .b = 0,
+        }, cell.content.color_rgb);
+    }
+
+    // Only y=1,2 are dirty because they are the ones that CHANGED contents
+    // (not just scroll).
+    try testing.expect(!s.pages.isDirty(.{ .active = .{ .x = 0, .y = 0 } }));
+    try testing.expect(s.pages.isDirty(.{ .active = .{ .x = 0, .y = 1 } }));
+    try testing.expect(s.pages.isDirty(.{ .active = .{ .x = 0, .y = 2 } }));
+}
+
+test "Screen: scroll above creates new page" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var s = try init(alloc, 10, 3, 10);
+    defer s.deinit();
+
+    // We need to get the cursor to a new page
+    const first_page_size = s.pages.pages.first.?.data.capacity.rows;
+    for (0..first_page_size - 3) |_| try s.testWriteString("\n");
+
+    try s.setAttribute(.{ .direct_color_bg = .{ .r = 155 } });
+    try s.testWriteString("1ABCD\n2EFGH\n3IJKL");
+    s.cursorAbsolute(0, 1);
+    s.pages.clearDirty();
+
+    // Ensure we're still on the first page
+    try testing.expect(s.cursor.page_pin.page == s.pages.pages.first.?);
+    try s.cursorScrollAbove();
+
+    // const stderr = std.io.getStdErr().writer();
+    // try s.pages.diagram(stderr);
+
+    {
+        const contents = try s.dumpStringAlloc(alloc, .{ .viewport = .{} });
+        defer alloc.free(contents);
+        try testing.expectEqualStrings("2EFGH\n\n3IJKL", contents);
+    }
+    {
+        const list_cell = s.pages.getCell(.{ .active = .{ .x = 0, .y = 1 } }).?;
+        const cell = list_cell.cell;
+        try testing.expect(cell.content_tag == .bg_color_rgb);
+        try testing.expectEqual(Cell.RGB{
+            .r = 155,
+            .g = 0,
+            .b = 0,
+        }, cell.content.color_rgb);
+    }
+
+    // Only y=1 is dirty because they are the ones that CHANGED contents
+    try testing.expect(!s.pages.isDirty(.{ .active = .{ .x = 0, .y = 0 } }));
+    try testing.expect(s.pages.isDirty(.{ .active = .{ .x = 0, .y = 1 } }));
+    try testing.expect(!s.pages.isDirty(.{ .active = .{ .x = 0, .y = 2 } }));
+}
+
+test "Screen: scroll above no scrollback bottom of page" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var s = try init(alloc, 10, 3, 0);
+    defer s.deinit();
+
+    const first_page_size = s.pages.pages.first.?.data.capacity.rows;
+    for (0..first_page_size - 3) |_| try s.testWriteString("\n");
+
+    try s.setAttribute(.{ .direct_color_bg = .{ .r = 155 } });
+    try s.testWriteString("1ABCD\n2EFGH\n3IJKL");
+    s.cursorAbsolute(0, 1);
+    s.pages.clearDirty();
+    try s.cursorScrollAbove();
+
+    {
+        const contents = try s.dumpStringAlloc(alloc, .{ .viewport = .{} });
+        defer alloc.free(contents);
+        try testing.expectEqualStrings("2EFGH\n\n3IJKL", contents);
+    }
+    {
+        const list_cell = s.pages.getCell(.{ .active = .{ .x = 0, .y = 1 } }).?;
+        const cell = list_cell.cell;
+        try testing.expect(cell.content_tag == .bg_color_rgb);
+        try testing.expectEqual(Cell.RGB{
+            .r = 155,
+            .g = 0,
+            .b = 0,
+        }, cell.content.color_rgb);
+    }
+
+    // Only y=1,2 are dirty because they are the ones that CHANGED contents
+    // (not just scroll).
+    try testing.expect(!s.pages.isDirty(.{ .active = .{ .x = 0, .y = 0 } }));
+    try testing.expect(s.pages.isDirty(.{ .active = .{ .x = 0, .y = 1 } }));
+    try testing.expect(s.pages.isDirty(.{ .active = .{ .x = 0, .y = 2 } }));
+}
+
 test "Screen: clone" {
     const testing = std.testing;
     const alloc = testing.allocator;