font/shaper: text runs should split around block cursors

Fixes #206

src/font/shaper/harfbuzz.zig

@@ -81,12 +81,14 @@ pub const Shaper = struct {
         group: *GroupCache,
         row: terminal.Screen.Row,
         selection: ?terminal.Selection,
+        cursor_x: ?usize,
     ) font.shape.RunIterator {
         return .{
             .hooks = .{ .shaper = self },
             .group = group,
             .row = row,
             .selection = selection,
+            .cursor_x = cursor_x,
         };
     }
 
@@ -169,7 +171,7 @@ test "run iterator" {
 
         // Get our run iterator
         var shaper = testdata.shaper;
-        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
         var count: usize = 0;
         while (try it.next(alloc)) |_| count += 1;
         try testing.expectEqual(@as(usize, 1), count);
@@ -182,7 +184,7 @@ test "run iterator" {
         try screen.testWriteString("ABCD   EFG");
 
         var shaper = testdata.shaper;
-        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
         var count: usize = 0;
         while (try it.next(alloc)) |_| count += 1;
         try testing.expectEqual(@as(usize, 1), count);
@@ -196,7 +198,7 @@ test "run iterator" {
 
         // Get our run iterator
         var shaper = testdata.shaper;
-        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
         var count: usize = 0;
         while (try it.next(alloc)) |_| {
             count += 1;
@@ -230,7 +232,7 @@ test "run iterator: empty cells with background set" {
 
         // Get our run iterator
         var shaper = testdata.shaper;
-        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -265,7 +267,7 @@ test "shape" {
 
     // Get our run iterator
     var shaper = testdata.shaper;
-    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
     var count: usize = 0;
     while (try it.next(alloc)) |run| {
         count += 1;
@@ -288,7 +290,7 @@ test "shape inconsolata ligs" {
         try screen.testWriteString(">=");
 
         var shaper = testdata.shaper;
-        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -305,7 +307,7 @@ test "shape inconsolata ligs" {
         try screen.testWriteString("===");
 
         var shaper = testdata.shaper;
-        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -330,7 +332,7 @@ test "shape emoji width" {
         try screen.testWriteString("👍");
 
         var shaper = testdata.shaper;
-        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -364,7 +366,7 @@ test "shape emoji width long" {
 
     // Get our run iterator
     var shaper = testdata.shaper;
-    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
     var count: usize = 0;
     while (try it.next(alloc)) |run| {
         count += 1;
@@ -395,7 +397,7 @@ test "shape variation selector VS15" {
 
     // Get our run iterator
     var shaper = testdata.shaper;
-    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
     var count: usize = 0;
     while (try it.next(alloc)) |run| {
         count += 1;
@@ -426,7 +428,7 @@ test "shape variation selector VS16" {
 
     // Get our run iterator
     var shaper = testdata.shaper;
-    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
     var count: usize = 0;
     while (try it.next(alloc)) |run| {
         count += 1;
@@ -454,7 +456,7 @@ test "shape with empty cells in between" {
 
     // Get our run iterator
     var shaper = testdata.shaper;
-    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
     var count: usize = 0;
     while (try it.next(alloc)) |run| {
         count += 1;
@@ -486,7 +488,7 @@ test "shape Chinese characters" {
 
     // Get our run iterator
     var shaper = testdata.shaper;
-    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
     var count: usize = 0;
     while (try it.next(alloc)) |run| {
         count += 1;
@@ -527,7 +529,7 @@ test "shape box glyphs" {
 
     // Get our run iterator
     var shaper = testdata.shaper;
-    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null);
+    var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
     var count: usize = 0;
     while (try it.next(alloc)) |run| {
         count += 1;
@@ -561,7 +563,7 @@ test "shape selection boundary" {
         var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), .{
             .start = .{ .x = 0, .y = 0 },
             .end = .{ .x = screen.cols - 1, .y = 0 },
-        });
+        }, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -577,7 +579,7 @@ test "shape selection boundary" {
         var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), .{
             .start = .{ .x = 2, .y = 0 },
             .end = .{ .x = screen.cols - 1, .y = 0 },
-        });
+        }, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -593,7 +595,7 @@ test "shape selection boundary" {
         var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), .{
             .start = .{ .x = 0, .y = 0 },
             .end = .{ .x = 3, .y = 0 },
-        });
+        }, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -609,7 +611,7 @@ test "shape selection boundary" {
         var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), .{
             .start = .{ .x = 1, .y = 0 },
             .end = .{ .x = 3, .y = 0 },
-        });
+        }, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -625,7 +627,7 @@ test "shape selection boundary" {
         var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), .{
             .start = .{ .x = 1, .y = 0 },
             .end = .{ .x = 1, .y = 0 },
-        });
+        }, null);
         var count: usize = 0;
         while (try it.next(alloc)) |run| {
             count += 1;
@@ -635,6 +637,71 @@ test "shape selection boundary" {
     }
 }
 
+test "shape cursor boundary" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var testdata = try testShaper(alloc);
+    defer testdata.deinit();
+
+    // Make a screen with some data
+    var screen = try terminal.Screen.init(alloc, 3, 10, 0);
+    defer screen.deinit();
+    try screen.testWriteString("a1b2c3d4e5");
+
+    // No cursor is full line
+    {
+        // Get our run iterator
+        var shaper = testdata.shaper;
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
+        var count: usize = 0;
+        while (try it.next(alloc)) |run| {
+            count += 1;
+            _ = try shaper.shape(run);
+        }
+        try testing.expectEqual(@as(usize, 1), count);
+    }
+
+    // Cursor at index 0 is two runs
+    {
+        // Get our run iterator
+        var shaper = testdata.shaper;
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, 0);
+        var count: usize = 0;
+        while (try it.next(alloc)) |run| {
+            count += 1;
+            _ = try shaper.shape(run);
+        }
+        try testing.expectEqual(@as(usize, 2), count);
+    }
+
+    // Cursor at index 1 is three runs
+    {
+        // Get our run iterator
+        var shaper = testdata.shaper;
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, 1);
+        var count: usize = 0;
+        while (try it.next(alloc)) |run| {
+            count += 1;
+            _ = try shaper.shape(run);
+        }
+        try testing.expectEqual(@as(usize, 3), count);
+    }
+
+    // Cursor at last col is two runs
+    {
+        // Get our run iterator
+        var shaper = testdata.shaper;
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, 9);
+        var count: usize = 0;
+        while (try it.next(alloc)) |run| {
+            count += 1;
+            _ = try shaper.shape(run);
+        }
+        try testing.expectEqual(@as(usize, 2), count);
+    }
+}
+
 const TestShaper = struct {
     alloc: Allocator,
     shaper: Shaper,

src/font/shaper/run.zig

@@ -29,6 +29,7 @@ pub const RunIterator = struct {
     group: *font.GroupCache,
     row: terminal.Screen.Row,
     selection: ?terminal.Selection = null,
+    cursor_x: ?usize = null,
     i: usize = 0,
 
     pub fn next(self: *RunIterator, alloc: Allocator) !?TextRun {
@@ -67,6 +68,32 @@ pub const RunIterator = struct {
                 }
             }
 
+            // If our cursor is on this line then we break the run around the
+            // cursor. This means that any row with a cursor has at least
+            // three breaks: before, exactly the cursor, and after.
+            if (self.cursor_x) |cursor_x| {
+                // Exactly: self.i is the cursor and we iterated once. This
+                // means that we started exactly at the cursor and did at
+                // least one (probably exactly one) iteration. That is
+                // exactly one character.
+                if (self.i == cursor_x and j > self.i) {
+                    assert(j == self.i + 1);
+                    break;
+                }
+
+                // Before: up to and not including the cursor. This means
+                // that we started before the cursor (self.i < cursor_x)
+                // and j is now at the cursor meaning we haven't yet processed
+                // the cursor.
+                if (self.i < cursor_x and j == cursor_x) {
+                    assert(j > 0);
+                    break;
+                }
+
+                // After: after the cursor. We don't need to do anything
+                // special, we just let the run complete.
+            }
+
             // If we're a spacer, then we ignore it
             if (cell.attrs.wide_spacer_tail) continue;
 

src/font/shaper/web_canvas.zig

@@ -60,12 +60,14 @@ pub const Shaper = struct {
         group: *font.GroupCache,
         row: terminal.Screen.Row,
         selection: ?terminal.Selection,
+        cursor_x: ?usize,
     ) font.shape.RunIterator {
         return .{
             .hooks = .{ .shaper = self },
             .group = group,
             .row = row,
             .selection = selection,
+            .cursor_x = cursor_x,
         };
     }
 
@@ -289,7 +291,7 @@ pub const Wasm = struct {
         while (rowIter.next()) |row| {
             defer y += 1;
 
-            var iter = self.runIterator(group, row, null);
+            var iter = self.runIterator(group, row, null, null);
             while (try iter.next(alloc)) |run| {
                 const cells = try self.shape(run);
                 log.info("y={} run={d} shape={any} idx={}", .{

src/renderer/Metal.zig

@@ -871,15 +871,31 @@ fn rebuildCells(
     while (rowIter.next()) |row| {
         defer y += 1;
 
-        // If this is the row with our cursor, then we may have to modify
+        // True if this is the row with our cursor. There are a lot of conditions
-        // the cell with the cursor.
+        // here because the reasons we need to know this are primarily to invert.
-        const start_i: usize = self.cells.items.len;
+        //
-        defer if (draw_cursor and
+        //   - If we aren't drawing the cursor (draw_cursor), then we don't need
+        //     to change our rendering.
+        //   - If the cursor is not visible, then we don't need to change rendering.
+        //   - If the cursor style is not a box, then we don't need to change
+        //     rendering because it'll never fully overlap a glyph.
+        //   - If the viewport is not at the bottom, then we don't need to
+        //     change rendering because the cursor is not visible.
+        //     (NOTE: this may not be fully correct, we may be scrolled
+        //     slightly up and the cursor may be visible)
+        //   - If this y doesn't match our cursor y then we don't need to
+        //     change rendering.
+        //
+        const cursor_row = draw_cursor and
             self.cursor_visible and
             self.cursor_style == .box and
             screen.viewportIsBottom() and
-            y == screen.cursor.y)
+            y == screen.cursor.y;
-        {
+
+        // If this is the row with our cursor, then we may have to modify
+        // the cell with the cursor.
+        const start_i: usize = self.cells.items.len;
+        defer if (cursor_row) {
             for (self.cells.items[start_i..]) |cell| {
                 if (cell.grid_pos[0] == @as(f32, @floatFromInt(screen.cursor.x)) and
                     cell.mode == .fg)
@@ -907,7 +923,12 @@ fn rebuildCells(
         };
 
         // Split our row into runs and shape each one.
-        var iter = self.font_shaper.runIterator(self.font_group, row, row_selection);
+        var iter = self.font_shaper.runIterator(
+            self.font_group,
+            row,
+            row_selection,
+            if (cursor_row) screen.cursor.x else null,
+        );
         while (try iter.next(self.alloc)) |run| {
             for (try self.font_shaper.shape(run)) |shaper_cell| {
                 if (self.updateCell(

src/renderer/OpenGL.zig

@@ -903,15 +903,17 @@ pub fn rebuildCells(
             break :sel null;
         };
 
-        // If this is the row with our cursor, then we may have to modify
+        // See Metal.zig
-        // the cell with the cursor.
+        const cursor_row = draw_cursor and
-        const start_i: usize = self.cells.items.len;
-        defer if (draw_cursor and
             self.cursor_visible and
             self.cursor_style == .box and
             screen.viewportIsBottom() and
-            y == screen.cursor.y)
+            y == screen.cursor.y;
-        {
+
+        // If this is the row with our cursor, then we may have to modify
+        // the cell with the cursor.
+        const start_i: usize = self.cells.items.len;
+        defer if (cursor_row) {
             for (self.cells.items[start_i..]) |cell| {
                 if (cell.grid_col == screen.cursor.x and
                     cell.mode == .fg)
@@ -942,7 +944,12 @@ pub fn rebuildCells(
         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, selection);
+        var iter = self.font_shaper.runIterator(
+            self.font_group,
+            row,
+            selection,
+            if (cursor_row) screen.cursor.x else null,
+        );
         while (try iter.next(self.alloc)) |run| {
             for (try self.font_shaper.shape(run)) |shaper_cell| {
                 if (self.updateCell(