move cell metrics calculation out into src/font

src/Grid.zig

@@ -166,56 +166,12 @@ pub fn init(
 
         break :group group;
     });
+    errdefer font_group.deinit(alloc);
 
     // Load all visible ASCII characters and build our cell width based on
     // the widest character that we see.
-    const cell_width: f32 = cell_width: {
-        var cell_width: f32 = 0;
-        var i: u32 = 32;
-        while (i <= 126) : (i += 1) {
-            const index = (try font_group.indexForCodepoint(alloc, .regular, i)).?;
-            const face = font_group.group.faceFromIndex(index);
-            const glyph_index = face.glyphIndex(i).?;
-            const glyph = try font_group.renderGlyph(alloc, index, glyph_index);
-            if (glyph.advance_x > cell_width) {
-                cell_width = @ceil(glyph.advance_x);
-            }
-        }
-
-        break :cell_width cell_width;
-    };
-
-    // The cell height is the vertical height required to render underscore
-    // '_' which should live at the bottom of a cell.
-    const cell_height: f32 = cell_height: {
-        // Get the '_' char for height
-        const index = (try font_group.indexForCodepoint(alloc, .regular, '_')).?;
-        const face = font_group.group.faceFromIndex(index);
-        const glyph_index = face.glyphIndex('_').?;
-        const glyph = try font_group.renderGlyph(alloc, index, glyph_index);
-
-        // This is the height reported by the font face
-        const face_height: i32 = face.unitsToPxY(face.face.handle.*.height);
-
-        // Determine the height of the underscore char
-        var res: i32 = face.unitsToPxY(face.face.handle.*.ascender);
-        res -= glyph.offset_y;
-        res += @intCast(i32, glyph.height);
-
-        // We take whatever is larger to account for some fonts that
-        // put the underscore outside f the rectangle.
-        if (res < face_height) res = face_height;
-
-        break :cell_height @intToFloat(f32, res);
-    };
-    const cell_baseline = cell_baseline: {
-        const face = font_group.group.faces.get(.regular).items[0];
-        break :cell_baseline cell_height - @intToFloat(
-            f32,
-            face.unitsToPxY(face.face.handle.*.ascender),
-        );
-    };
-    log.debug("cell dimensions w={d} h={d} baseline={d}", .{ cell_width, cell_height, cell_baseline });
+    const metrics = try font_group.metrics(alloc);
+    log.debug("cell dimensions={}", .{metrics});
 
     // Create our shader
     const program = try gl.Program.createVF(
@@ -226,8 +182,8 @@ pub fn init(
     // Set our cell dimensions
     const pbind = try program.use();
     defer pbind.unbind();
-    try program.setUniform("cell_size", @Vector(2, f32){ cell_width, cell_height });
-    try program.setUniform("glyph_baseline", cell_baseline);
+    try program.setUniform("cell_size", @Vector(2, f32){ metrics.cell_width, metrics.cell_height });
+    try program.setUniform("glyph_baseline", metrics.cell_baseline);
 
     // Set all of our texture indexes
     try program.setUniform("text", 0);
@@ -328,7 +284,7 @@ pub fn init(
     return Grid{
         .alloc = alloc,
         .cells = .{},
-        .cell_size = .{ .width = cell_width, .height = cell_height },
+        .cell_size = .{ .width = metrics.cell_width, .height = metrics.cell_height },
         .size = .{ .rows = 0, .columns = 0 },
         .program = program,
         .vao = vao,

src/font/GroupCache.zig

@@ -11,6 +11,7 @@ const Library = @import("main.zig").Library;
 const Glyph = @import("main.zig").Glyph;
 const Style = @import("main.zig").Style;
 const Group = @import("main.zig").Group;
+const Metrics = @import("main.zig").Metrics;
 
 const log = std.log.scoped(.font_groupcache);
 
@@ -80,6 +81,66 @@ pub fn reset(self: *GroupCache) void {
     self.glyphs.clearRetainingCapacity();
 }
 
+/// Calculate the metrics for this group. This also warms the cache
+/// since this preloads all the ASCII characters.
+pub fn metrics(self: *GroupCache, alloc: Allocator) !Metrics {
+    // Load all visible ASCII characters and build our cell width based on
+    // the widest character that we see.
+    const cell_width: f32 = cell_width: {
+        var cell_width: f32 = 0;
+        var i: u32 = 32;
+        while (i <= 126) : (i += 1) {
+            const index = (try self.indexForCodepoint(alloc, .regular, i)).?;
+            const face = self.group.faceFromIndex(index);
+            const glyph_index = face.glyphIndex(i).?;
+            const glyph = try self.renderGlyph(alloc, index, glyph_index);
+            if (glyph.advance_x > cell_width) {
+                cell_width = @ceil(glyph.advance_x);
+            }
+        }
+
+        break :cell_width cell_width;
+    };
+
+    // The cell height is the vertical height required to render underscore
+    // '_' which should live at the bottom of a cell.
+    const cell_height: f32 = cell_height: {
+        // Get the '_' char for height
+        const index = (try self.indexForCodepoint(alloc, .regular, '_')).?;
+        const face = self.group.faceFromIndex(index);
+        const glyph_index = face.glyphIndex('_').?;
+        const glyph = try self.renderGlyph(alloc, index, glyph_index);
+
+        // This is the height reported by the font face
+        const face_height: i32 = face.unitsToPxY(face.face.handle.*.height);
+
+        // Determine the height of the underscore char
+        var res: i32 = face.unitsToPxY(face.face.handle.*.ascender);
+        res -= glyph.offset_y;
+        res += @intCast(i32, glyph.height);
+
+        // We take whatever is larger to account for some fonts that
+        // put the underscore outside f the rectangle.
+        if (res < face_height) res = face_height;
+
+        break :cell_height @intToFloat(f32, res);
+    };
+
+    const cell_baseline = cell_baseline: {
+        const face = self.group.faces.get(.regular).items[0];
+        break :cell_baseline cell_height - @intToFloat(
+            f32,
+            face.unitsToPxY(face.face.handle.*.ascender),
+        );
+    };
+
+    return Metrics{
+        .cell_width = cell_width,
+        .cell_height = cell_height,
+        .cell_baseline = cell_baseline,
+    };
+}
+
 /// Get the font index for a given codepoint. This is cached.
 pub fn indexForCodepoint(self: *GroupCache, alloc: Allocator, style: Style, cp: u32) !?Group.FontIndex {
     const key: CodepointKey = .{ .style = style, .codepoint = cp };

src/font/main.zig

@@ -14,16 +14,15 @@ pub const Style = enum(u2) {
     bold_italic = 3,
 };
 
-/// Returns the UTF-32 codepoint for the given value.
-pub fn codepoint(v: anytype) u32 {
-    // We need a UTF32 codepoint for freetype
-    return switch (@TypeOf(v)) {
-        u32 => v,
-        comptime_int, u8 => @intCast(u32, v),
-        []const u8 => @intCast(u32, try std.unicode.utfDecode(v)),
-        else => @compileError("invalid codepoint type"),
-    };
-}
+/// Font metrics useful for things such as grid calculation.
+pub const Metrics = struct {
+    /// The width and height of a monospace cell.
+    cell_width: f32,
+    cell_height: f32,
+
+    /// The baseline offset that can be used to place underlines.
+    cell_baseline: f32,
+};
 
 test {
     @import("std").testing.refAllDecls(@This());