implement LRU row GPU cell caching

src/Grid.zig

@@ -12,9 +12,12 @@ const Terminal = terminal.Terminal;
 const gl = @import("opengl.zig");
 const trace = @import("tracy").trace;
 const math = @import("math.zig");
+const lru = @import("lru.zig");
 
 const log = std.log.scoped(.grid);
 
+const CellsLRU = lru.AutoHashMap(terminal.Screen.RowHeader.Id, std.ArrayListUnmanaged(GPUCell));
+
 alloc: std.mem.Allocator,
 
 /// Current dimensions for this grid.
@@ -26,6 +29,10 @@ cell_size: CellSize,
 /// The current set of cells to render.
 cells: std.ArrayListUnmanaged(GPUCell),
 
+/// The LRU that stores our GPU cells cached by row IDs. This is used to
+/// prevent high CPU activity when shaping rows.
+cells_lru: CellsLRU,
+
 /// The size of the cells list that was sent to the GPU. This is used
 /// to detect when the cells array was reallocated/resized and handle that
 /// accordingly.
@@ -303,6 +310,7 @@ pub fn init(
     return Grid{
         .alloc = alloc,
         .cells = .{},
+        .cells_lru = CellsLRU.init(0),
         .cell_size = .{ .width = metrics.cell_width, .height = metrics.cell_height },
         .size = .{ .rows = 0, .columns = 0 },
         .program = program,
@@ -333,6 +341,7 @@ pub fn deinit(self: *Grid) void {
     self.ebo.destroy();
     self.vao.destroy();
     self.program.destroy();
+    self.cells_lru.deinit(self.alloc);
     self.cells.deinit(self.alloc);
     self.* = undefined;
 }
@@ -369,6 +378,22 @@ pub fn rebuildCells(self: *Grid, term: *Terminal) !void {
     while (rowIter.next()) |row| {
         defer y += 1;
 
+        // Get our value from the cache.
+        const gop = try self.cells_lru.getOrPut(self.alloc, row.getId());
+        if (!row.isDirty() and gop.found_existing) {
+            var i: usize = self.cells.items.len;
+            for (gop.value_ptr.items) |cell| {
+                self.cells.appendAssumeCapacity(cell);
+                self.cells.items[i].grid_row = @intCast(u16, y);
+                i += 1;
+            }
+
+            continue;
+        }
+
+        // Get the starting index for our row so we can cache any new GPU cells.
+        const start = self.cells.items.len;
+
         // Split our row into runs and shape each one.
         var iter = self.font_shaper.runIterator(&self.font_group, row);
         while (try iter.next(self.alloc)) |run| {
@@ -383,6 +408,18 @@ pub fn rebuildCells(self: *Grid, term: *Terminal) !void {
                 ));
             }
         }
+
+        // Initialize our list
+        if (!gop.found_existing) gop.value_ptr.* = .{};
+        var row_cells = gop.value_ptr;
+
+        // Get our new length and cache the cells.
+        try row_cells.ensureTotalCapacity(self.alloc, term.screen.cols);
+        row_cells.clearRetainingCapacity();
+        row_cells.appendSliceAssumeCapacity(self.cells.items[start..]);
+
+        // Set row is not dirty anymore
+        row.setDirty(false);
     }
 
     // Add the cursor
@@ -625,6 +662,12 @@ pub fn setScreenSize(self: *Grid, dim: ScreenSize) !void {
     // Recalculate the rows/columns.
     self.size.update(dim, self.cell_size);
 
+    // Update our LRU. We arbitrarily support a certain number of pages here.
+    // We also always support a minimum number of caching in case a user
+    // is resizing tiny then growing again we can save some of the renders.
+    const evicted = try self.cells_lru.resize(self.alloc, @maximum(80, self.size.rows * 10));
+    if (evicted) |list| for (list) |*value| value.deinit(self.alloc);
+
     // Update our shaper
     var shape_buf = try self.alloc.alloc(font.Shaper.Cell, self.size.columns * 2);
     errdefer self.alloc.free(shape_buf);

src/lru.zig

@@ -164,26 +164,30 @@ pub fn HashMap(
         }
 
         /// Resize the LRU. If this shrinks the LRU then LRU items will be
-        /// deallocated.
+        /// deallocated. The deallocated items are returned in the slice. This
-        pub fn resize(self: *Self, alloc: Allocator, capacity: Map.Size) void {
+        /// slice must be freed by the caller.
+        pub fn resize(self: *Self, alloc: Allocator, capacity: Map.Size) Allocator.Error!?[]V {
             // Fastest
             if (capacity >= self.capacity) {
                 self.capacity = capacity;
-                return;
+                return null;
             }
 
             // If we're shrinking but we're smaller than the new capacity,
             // then we don't have to do anything.
             if (self.map.count() <= capacity) {
                 self.capacity = capacity;
-                return;
+                return null;
             }
 
             // We're shrinking and we have more items than the new capacity
             const delta = self.map.count() - capacity;
+            var evicted = try alloc.alloc(V, delta);
+
             var i: Map.Size = 0;
             while (i < delta) : (i += 1) {
                 var node = self.queue.first.?;
+                evicted[i] = node.data.value;
                 self.queue.remove(node);
                 _ = self.map.remove(node.data.key);
                 alloc.destroy(node);
@@ -191,6 +195,8 @@ pub fn HashMap(
 
             self.capacity = capacity;
             assert(self.map.count() == capacity);
+
+            return evicted;
         }
     };
 }
@@ -281,7 +287,8 @@ test "resize shrink without removal" {
     }
 
     // Shrink
-    m.resize(alloc, 1);
+    const evicted = try m.resize(alloc, 1);
+    try testing.expect(evicted == null);
     {
         const gop = try m.getOrPut(alloc, 1);
         try testing.expect(gop.found_existing);
@@ -311,7 +318,9 @@ test "resize shrink and remove" {
     }
 
     // Shrink
-    m.resize(alloc, 1);
+    const evicted = try m.resize(alloc, 1);
+    defer alloc.free(evicted.?);
+    try testing.expectEqual(@as(usize, 1), evicted.?.len);
     {
         const gop = try m.getOrPut(alloc, 1);
         try testing.expect(!gop.found_existing);

src/terminal/Screen.zig

@@ -113,7 +113,7 @@ const StorageCell = union {
 /// The row header is at the start of every row within the storage buffer.
 /// It can store row-specific data.
 pub const RowHeader = struct {
-    const Id = u32;
+    pub const Id = u32;
 
     /// The ID of this row, used to uniquely identify this row. The cells
     /// are also ID'd by id + cell index (0-indexed). This will wrap around
@@ -2463,13 +2463,22 @@ test "Screen: resize (no reflow) more rows" {
     defer s.deinit();
     const str = "1ABCD\n2EFGH\n3IJKL";
     try s.testWriteString(str);
-    try s.resizeWithoutReflow(10, 5);
 
+    // Clear dirty rows
+    var iter = s.rowIterator(.viewport);
+    while (iter.next()) |row| row.setDirty(false);
+
+    // Resize
+    try s.resizeWithoutReflow(10, 5);
     {
         var contents = try s.testString(alloc, .viewport);
         defer alloc.free(contents);
         try testing.expectEqualStrings(str, contents);
     }
+
+    // Everything should be dirty
+    iter = s.rowIterator(.viewport);
+    while (iter.next()) |row| try testing.expect(row.isDirty());
 }
 
 test "Screen: resize (no reflow) less rows" {