font: respect cell width attributes in nerd font constraints

This mostly applies to powerline glyphs, but is also relevant for heavy
bracket characters, which need to always be 1 wide otherwise they look
silly because they misalign depending on if there's a space after them
or not.

src/font/face.zig

@@ -147,6 +147,9 @@ pub const RenderOptions = struct {
         /// Maximum ratio of width to height when resizing.
         max_xy_ratio: ?f64 = null,
 
+        /// Maximum number of cells horizontally to use.
+        max_constraint_width: u2 = 2,
+
         pub const Size = enum {
             /// Don't change the size of this glyph.
             none,
@@ -186,16 +189,26 @@ pub const RenderOptions = struct {
         pub fn constrain(
             self: Constraint,
             glyph: GlyphSize,
-            /// Available width
+            /// Width of one cell.
             cell_width: f64,
-            /// Available height
+            /// Height of one cell.
             cell_height: f64,
+            /// Number of cells horizontally available for this glyph.
+            constraint_width: u2,
         ) GlyphSize {
             var g = glyph;
 
-            const w = cell_width -
-                self.pad_left * cell_width -
-                self.pad_right * cell_width;
+            const available_width =
+                cell_width * @as(f64, @floatFromInt(
+                    @min(
+                        self.max_constraint_width,
+                        constraint_width,
+                    ),
+                ));
+
+            const w = available_width -
+                self.pad_left * available_width -
+                self.pad_right * available_width;
             const h = cell_height -
                 self.pad_top * cell_height -
                 self.pad_bottom * cell_height;
@@ -203,7 +216,7 @@ pub const RenderOptions = struct {
             // Subtract padding from the bearings so that our
             // alignment and sizing code works correctly. We
             // re-add before returning.
-            g.x -= self.pad_left * cell_width;
+            g.x -= self.pad_left * available_width;
             g.y -= self.pad_bottom * cell_height;
 
             switch (self.size_horizontal) {
@@ -305,7 +318,7 @@ pub const RenderOptions = struct {
             }
 
             // Re-add our padding before returning.
-            g.x += self.pad_left * cell_width;
+            g.x += self.pad_left * available_width;
             g.y += self.pad_bottom * cell_height;
 
             return g;

src/font/face/coretext.zig

@@ -337,7 +337,7 @@ pub const Face = struct {
             };
 
         const metrics = opts.grid_metrics;
-        const cell_width: f64 = @floatFromInt(metrics.cell_width * opts.constraint_width);
+        const cell_width: f64 = @floatFromInt(metrics.cell_width);
         const cell_height: f64 = @floatFromInt(metrics.cell_height);
 
         const glyph_size = opts.constraint.constrain(
@@ -349,6 +349,7 @@ pub const Face = struct {
             },
             cell_width,
             cell_height,
+            opts.constraint_width,
         );
 
         const width = glyph_size.width;

src/font/face/freetype.zig

@@ -390,7 +390,7 @@ pub const Face = struct {
         // Next we need to apply any constraints.
         const metrics = opts.grid_metrics;
 
-        const cell_width: f64 = @floatFromInt(metrics.cell_width * opts.constraint_width);
+        const cell_width: f64 = @floatFromInt(metrics.cell_width);
         const cell_height: f64 = @floatFromInt(metrics.cell_height);
 
         const glyph_x: f64 = f26dot6ToF64(glyph.*.metrics.horiBearingX);
@@ -405,6 +405,7 @@ pub const Face = struct {
             },
             cell_width,
             cell_height,
+            opts.constraint_width,
         );
 
         const width = glyph_size.width;

src/font/nerd_font_attributes.zig

@@ -13,6 +13,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .center,
             .align_vertical = .center,
             .pad_left = -0.02,
@@ -24,6 +25,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .cover,
             .size_vertical = .fit,
+            .max_constraint_width = 1,
             .align_horizontal = .center,
             .align_vertical = .center,
             .pad_left = 0.1,
@@ -35,6 +37,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .cover,
             .size_vertical = .fit,
+            .max_constraint_width = 1,
             .align_horizontal = .center,
             .align_vertical = .center,
             .pad_top = 0.3,
@@ -44,6 +47,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .pad_left = -0.06,
@@ -56,6 +60,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .max_xy_ratio = 0.7,
@@ -64,6 +69,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
             .pad_left = -0.06,
@@ -76,6 +82,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
             .max_xy_ratio = 0.7,
@@ -84,6 +91,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .pad_left = -0.06,
@@ -96,6 +104,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .max_xy_ratio = 0.5,
@@ -104,6 +113,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
             .pad_left = -0.06,
@@ -116,6 +126,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
             .max_xy_ratio = 0.5,
@@ -125,6 +136,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .pad_left = -0.05,
@@ -137,6 +149,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
         },
@@ -145,6 +158,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
             .pad_left = -0.05,
@@ -157,6 +171,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
         },
@@ -287,6 +302,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .pad_left = -0.02,
@@ -299,6 +315,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
             .pad_left = -0.02,
@@ -311,6 +328,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .pad_left = -0.05,
@@ -323,6 +341,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
             .pad_left = -0.05,

src/font/nerd_font_codegen.py

@@ -190,6 +190,12 @@ def emit_zig_entry_multikey(codepoints: list[int], attr: PatchSetAttributeEntry)
         s += "            .size_horizontal = .fit,\n"
         s += "            .size_vertical = .fit,\n"
 
+    # There are two cases where we want to limit the constraint width to 1:
+    # - If there's a `1` in the stretch mode string.
+    # - If the stretch mode is `xy` and there's not an explicit `2`.
+    if "1" in stretch or ("xy" in stretch and "2" not in stretch):
+        s += "            .max_constraint_width = 1,\n"
+
     if align is not None:
         s += f"            .align_horizontal = {align},\n"
     if valign is not None: