hook up scrolling, kind of works, kind of broke

src/Window.zig

@@ -250,6 +250,7 @@ pub fn create(alloc: Allocator, loop: libuv.Loop, config: *const Config) !*Windo
     window.setKeyCallback(keyCallback);
     window.setFocusCallback(focusCallback);
     window.setRefreshCallback(refreshCallback);
+    window.setScrollCallback(scrollCallback);
 
     return self;
 }
@@ -505,6 +506,24 @@ fn refreshCallback(window: glfw.Window) void {
     win.render_timer.schedule() catch unreachable;
 }
 
+fn scrollCallback(window: glfw.Window, xoff: f64, yoff: f64) void {
+    const win = window.getUserPointer(Window) orelse return;
+
+    //log.info("SCROLL: {} {}", .{ xoff, yoff });
+    _ = xoff;
+
+    // Positive is up
+    const sign: isize = if (yoff < 0) -1 else 1;
+    const delta: isize = sign * @maximum(@divFloor(win.grid.size.rows, 15), 1);
+    log.info("scroll: delta={}", .{delta});
+    win.terminal.scrollViewport(.{ .delta = delta });
+
+    // Schedule render since scrolling usually does something.
+    // TODO(perf): we can only schedule render if we know scrolling
+    // did something
+    win.render_timer.schedule() catch unreachable;
+}
+
 fn cursorTimerCallback(t: *libuv.Timer) void {
     const tracy = trace(@src());
     defer tracy.end();

src/terminal/Screen.zig

@@ -187,12 +187,25 @@ pub fn scroll(self: *Screen, behavior: Scroll) void {
         .bottom => self.visible_offset = self.bottom - self.rows,
 
         // TODO: deltas greater than the entire scrollback
-        .delta => |delta| self.scrollDown(delta, true),
-        .delta_no_grow => |delta| self.scrollDown(delta, false),
+        .delta => |delta| self.scrollDelta(delta, true),
+        .delta_no_grow => |delta| self.scrollDelta(delta, false),
     }
 }
 
-fn scrollDown(self: *Screen, delta: isize, grow: bool) void {
+fn scrollDelta(self: *Screen, delta: isize, grow: bool) void {
+    log.info("offsets before: top={} bottom={} visible={}", .{
+        self.top,
+        self.bottom,
+        self.visible_offset,
+    });
+    defer {
+        log.info("offsets after: top={} bottom={} visible={}", .{
+            self.top,
+            self.bottom,
+            self.visible_offset,
+        });
+    }
+
     // If we're scrolling up, then we just subtract and we're done.
     if (delta < 0) {
         self.visible_offset -|= @intCast(usize, -delta);
@@ -255,22 +268,6 @@ fn scrollDown(self: *Screen, delta: isize, grow: bool) void {
     self.visible_offset -= rows_overlapped;
 }
 
-/// Scroll the screen up (positive) or down (negative). Scrolling direction
-/// is the direction text would move. For example, scrolling down would
-/// move existing text downward.
-pub fn scrollOld(self: *Screen, count: isize) void {
-    if (count < 0) {
-        const amount = @mod(@intCast(usize, -count), self.rows);
-        if (amount > self.top) {
-            self.top = self.rows - amount;
-        } else {
-            self.top -|= amount;
-        }
-    } else {
-        self.top = @mod(self.top + @intCast(usize, count), self.rows);
-    }
-}
-
 /// Copy row at src to dst.
 pub fn copyRow(self: *Screen, dst: usize, src: usize) void {
     const src_row = self.getRow(src);
@@ -289,7 +286,7 @@ pub fn resize(self: *Screen, alloc: Allocator, rows: usize, cols: usize) !void {
     const old = self.*;
 
     // Reallocate the storage
-    self.storage = try alloc.alloc(Cell, rows * cols);
+    self.storage = try alloc.alloc(Cell, (rows + self.max_scrollback) * cols);
     self.top = 0;
     self.bottom = rows - 1;
     self.rows = rows;

src/terminal/Terminal.zig

@@ -73,7 +73,8 @@ pub fn init(alloc: Allocator, cols: usize, rows: usize) !Terminal {
     return Terminal{
         .cols = cols,
         .rows = rows,
-        .screen = try Screen.init(alloc, rows, cols, 0),
+        // TODO: configurable scrollback
+        .screen = try Screen.init(alloc, rows, cols, 1000),
         .cursor = .{},
         .saved_cursor = .{},
         .tabstops = try Tabstops.init(alloc, cols, TABSTOP_INTERVAL),
@@ -276,7 +277,7 @@ pub fn index(self: *Terminal) void {
         if (self.cursor.y < self.scrolling_region.top or
             self.cursor.y > self.scrolling_region.bottom) return;
 
-        self.scrollUp();
+        self.screen.scroll(.{ .delta = 1 });
         return;
     }
 
@@ -673,16 +674,6 @@ pub fn deleteLines(self: *Terminal, count: usize) void {
     }
 }
 
-/// Scroll the text up by one row.
-pub fn scrollUp(self: *Terminal) void {
-    const tracy = trace(@src());
-    defer tracy.end();
-
-    self.screen.scroll(.{ .delta = 1 });
-    const last = self.screen.getRow(self.rows - 1);
-    for (last) |*cell| cell.char = 0;
-}
-
 /// Scroll the text down by one row.
 /// TODO: test
 pub fn scrollDown(self: *Terminal, count: usize) void {
@@ -698,6 +689,18 @@ pub fn scrollDown(self: *Terminal, count: usize) void {
     self.insertLines(count);
 }
 
+/// Options for scrolling the viewport of the terminal grid.
+pub const ScrollViewport = union(enum) {
+    delta: isize,
+};
+
+/// Scroll the viewport of the terminal grid.
+pub fn scrollViewport(self: *Terminal, behavior: ScrollViewport) void {
+    self.screen.scroll(switch (behavior) {
+        .delta => |delta| .{ .delta_no_grow = delta },
+    });
+}
+
 /// Set Top and Bottom Margins If bottom is not specified, 0 or bigger than
 /// the number of the bottom-most row, it is adjusted to the number of the
 /// bottom most row.