font: web canvas shaper yields runs

example/app.ts

@@ -46,6 +46,9 @@ fetch(url.href).then(response =>
     atlas_new,
     atlas_free,
     atlas_debug_canvas,
+    shaper_new,
+    shaper_free,
+    shaper_test,
   } = results.instance.exports;
   // Give us access to the zjs value for debugging.
   globalThis.zjs = zjs;
@@ -54,13 +57,19 @@ fetch(url.href).then(response =>
   // Initialize our zig-js memory
   zjs.memory = memory;
 
+  // Helpers
+  const makeStr = (str) => {
+    const utf8 = new TextEncoder().encode(str);
+    const ptr = malloc(utf8.byteLength);
+    new Uint8Array(memory.buffer, ptr).set(utf8);
+    return { ptr: ptr, len: utf8.byteLength };
+  };
+
   // Create our atlas
   // const atlas = atlas_new(512, 0 /* greyscale */);
 
   // Create some memory for our string
-  const font = new TextEncoder().encode("monospace");
-  const font_ptr = malloc(font.byteLength);
-    new Uint8Array(memory.buffer, font_ptr).set(font);
+  const font_name = makeStr("monospace");
 
   // Initialize our deferred face
   // const df = deferred_face_new(font_ptr, font.byteLength, 0 /* text */);
@@ -73,8 +82,8 @@ fetch(url.href).then(response =>
 
   // Create our group
   const group = group_new(72 /* size */);
-  group_add_face(group, 0 /* regular */, deferred_face_new(font_ptr, font.byteLength, 0 /* text */));
-  group_add_face(group, 0 /* regular */, deferred_face_new(font_ptr, font.byteLength, 1 /* emoji */));
+  group_add_face(group, 0 /* regular */, deferred_face_new(font_name.ptr, font_name.len, 0 /* text */));
+  group_add_face(group, 0 /* regular */, deferred_face_new(font_name.ptr, font_name.len, 1 /* emoji */));
 
   // Create our group cache
   const group_cache = group_cache_new(group);
@@ -112,5 +121,10 @@ fetch(url.href).then(response =>
     document.getElementById("atlas-color-canvas").append(zjs.deleteValue(id));
   }
 
+  // Let's try shaping
+  const shaper = shaper_new(120);
+  const input = makeStr("hello");
+  shaper_test(shaper, group_cache, input.ptr, input.len);
+
     //face_free(face);
 });

src/font/shaper/web_canvas.zig

@@ -40,6 +40,19 @@ pub const Shaper = struct {
         return .{ .hooks = .{ .shaper = self }, .group = group, .row = row };
     }
 
+    /// Shape the given text run. The text run must be the immediately previous
+    /// text run that was iterated since the text run does share state with the
+    /// Shaper struct.
+    ///
+    /// The return value is only valid until the next shape call is called.
+    ///
+    /// If there is not enough space in the cell buffer, an error is returned.
+    pub fn shape(self: *Shaper, run: font.shape.TextRun) ![]font.shape.Cell {
+        _ = self;
+        _ = run;
+        return error.Unimplemented;
+    }
+
     /// The hooks for RunIterator.
     pub const RunIteratorHook = struct {
         shaper: *Shaper,
@@ -51,7 +64,7 @@ pub const Shaper = struct {
 
         pub fn addCodepoint(self: RunIteratorHook, cp: u32, cluster: u32) !void {
             _ = cluster;
-            try self.shaper.append(cp);
+            try self.shaper.run_buf.append(cp);
         }
 
         pub fn finalize(self: RunIteratorHook) !void {
@@ -64,4 +77,60 @@ pub const Shaper = struct {
 pub const Wasm = struct {
     const wasm = @import("../../os/wasm.zig");
     const alloc = wasm.alloc;
+
+    export fn shaper_new(cap: usize) ?*Shaper {
+        return shaper_new_(cap) catch null;
+    }
+
+    fn shaper_new_(cap: usize) !*Shaper {
+        var cell_buf = try alloc.alloc(font.shape.Cell, cap);
+        errdefer alloc.free(cell_buf);
+
+        var shaper = try Shaper.init(alloc, cell_buf);
+        errdefer shaper.deinit();
+
+        var result = try alloc.create(Shaper);
+        errdefer alloc.destroy(result);
+        result.* = shaper;
+        return result;
+    }
+
+    export fn shaper_free(ptr: ?*Shaper) void {
+        if (ptr) |v| {
+            alloc.free(v.cell_buf);
+            v.deinit();
+            alloc.destroy(v);
+        }
+    }
+
+    /// Runs a test to verify shaping works properly.
+    export fn shaper_test(
+        self: *Shaper,
+        group: *font.GroupCache,
+        str: [*]const u8,
+        len: usize,
+    ) void {
+        shaper_test_(self, group, str[0..len]) catch |err| {
+            log.warn("error during shaper test err={}", .{err});
+        };
+    }
+
+    fn shaper_test_(self: *Shaper, group: *font.GroupCache, str: []const u8) !void {
+        // Create a terminal and print all our characters into it.
+        var term = try terminal.Terminal.init(alloc, self.cell_buf.len, 80);
+        defer term.deinit(alloc);
+        for (str) |c| try term.print(c);
+
+        // Iterate over the rows and print out all the runs we get.
+        var rowIter = term.screen.rowIterator(.viewport);
+        var y: usize = 0;
+        while (rowIter.next()) |row| {
+            defer y += 1;
+
+            var iter = self.runIterator(group, row);
+            while (try iter.next(alloc)) |run| {
+                log.info("y={} run={}", .{ y, run });
+            }
+        }
+    }
 };