test rendering box glyphs, looks OKAY

src/Window.zig

@@ -289,6 +289,17 @@ pub fn create(alloc: Allocator, app: *App, config: *const Config) !*Window {
     // Pre-calculate our initial cell size ourselves.
     const cell_size = try renderer.CellSize.init(alloc, font_group);
 
+    // Setup our box font
+    font_group.group.box_font = font.BoxFont{
+        .width = @floatToInt(u32, cell_size.width),
+        .height = @floatToInt(u32, cell_size.height),
+        .thickness = 2,
+    };
+
+    // TEST
+    const idx = (try font_group.indexForCodepoint(alloc, 0x2500, .regular, null)).?;
+    _ = try font_group.renderGlyph(alloc, idx, 0x2500, null);
+
     // Convert our padding from points to pixels
     const padding_x = (@intToFloat(f32, config.@"window-padding-x") * x_dpi) / 72;
     const padding_y = (@intToFloat(f32, config.@"window-padding-y") * y_dpi) / 72;

src/font/Group.zig

@@ -237,7 +237,19 @@ fn indexForCodepointExact(self: Group, cp: u32, style: Style, p: ?Presentation)
     return null;
 }
 
-/// Return the Face represented by a given FontIndex.
+/// Returns the presentation for a specific font index. This is useful for
+/// determining what atlas is needed.
+pub fn presentationFromIndex(self: Group, index: FontIndex) !font.Presentation {
+    if (index.special()) |sp| switch (sp) {
+        .box => return .text,
+    };
+
+    const face = try self.faceFromIndex(index);
+    return face.presentation;
+}
+
+/// Return the Face represented by a given FontIndex. Note that special
+/// fonts (i.e. box glyphs) do not have a face.
 pub fn faceFromIndex(self: Group, index: FontIndex) !Face {
     if (index.special() != null) return error.SpecialHasNoFace;
     const deferred = &self.faces.get(index.style).items[@intCast(usize, index.idx)];

src/font/GroupCache.zig

@@ -132,8 +132,10 @@ pub fn renderGlyph(
     if (gop.found_existing) return gop.value_ptr.*;
 
     // Uncached, render it
-    const face = try self.group.faceFromIndex(index);
-    const atlas: *Atlas = if (face.presentation == .emoji) &self.atlas_color else &self.atlas_greyscale;
+    const atlas: *Atlas = switch (try self.group.presentationFromIndex(index)) {
+        .text => &self.atlas_greyscale,
+        .emoji => &self.atlas_color,
+    };
     const glyph = self.group.renderGlyph(
         alloc,
         atlas,

src/renderer/OpenGL.zig

@@ -501,6 +501,12 @@ pub fn setFontSize(self: *OpenGL, size: font.face.DesiredSize) !void {
     if (std.meta.eql(self.cell_size, new_cell_size)) return;
     self.cell_size = new_cell_size;
 
+    // Set the cell size of the box font
+    if (self.font_group.group.box_font) |*box| {
+        box.width = @floatToInt(u32, self.cell_size.width);
+        box.height = @floatToInt(u32, self.cell_size.height);
+    }
+
     // Notify the window that the cell size changed.
     _ = self.window_mailbox.push(.{
         .cell_size = new_cell_size,