feat: render a string with freetype

src/main.zig

@@ -461,22 +461,40 @@ const Canvas = struct {
         const top = pos[1];
         const right = @min(left + cols, width);
         const bottom = @min(top + rows, height);
-        const buffer = bitmap.buffer().?;
+        const buffer = bitmap.buffer() orelse return;
         if (pos[0] > width or pos[1] > height) return;
         for (top..bottom, 0..) |y, i| {
             const row = fb[y * width .. (y + 1) * width];
             for (left..right, 0..) |x, a| {
                 const pixel = &row[x];
                 const intensity = buffer[i * cols + a];
-                pixel.* = .{
-                    intensity,
-                    intensity,
-                    intensity,
-                    0xFF,
-                };
+                if (intensity != 0) {
+                    pixel.* = .{
+                        intensity,
+                        intensity,
+                        intensity,
+                        0xFF,
+                    };
+                }
             }
         }
     }
+
+    fn print(canvas: Canvas, face: freetype.Face, string: []const u8, pos: [2]u32) !void {
+        const unicode_view = try std.unicode.Utf8View.init(string);
+        var unicode_iter = unicode_view.iterator();
+        var x: i32 = @intCast(pos[0]);
+        var y: i32 = @intCast(pos[1]);
+        while (unicode_iter.nextCodepoint()) |codepoint| {
+            const glyph_index = face.getCharIndex(codepoint) orelse continue;
+            try face.loadGlyph(glyph_index, .{ .render = true });
+            const glyph = face.glyph();
+            const bitmap = glyph.bitmap();
+            canvas.blitFreetypeBitmap(bitmap, .{ @intCast(x + glyph.bitmapLeft()), @intCast(y - glyph.bitmapTop()) });
+            x += @intCast(glyph.advance().x >> 6);
+            y += @intCast(glyph.advance().y >> 6);
+        }
+    }
 };
 
 fn wmbaseHandler(app: *App, header: wayland.Header, body: []const u32) !void {
@@ -523,10 +541,8 @@ fn surfaceDesktopHandler(app: *App, header: wayland.Header, body: []const u32) !
 
             // render
             const canvas = try pool.getFramebuffer(.{ width, height });
-            try app.font_face.loadChar('H', .{ .render = true });
-            const bitmap = app.font_face.glyph().bitmap();
             canvas.renderGradient();
-            canvas.blitFreetypeBitmap(bitmap, .{ 0, 0 });
+            try canvas.print(app.font_face, "Hello, World!", .{ 10, 60 });
             try canvas.attach(app.surface);
             try app.callbacks.put(canvas.buffer.id, bufferHandler);
         },