Nerd Font Constraint Fixes (#7834)

Fixes #7820, and while fixing that I noticed that we need to respect the
cell width constraints since certain glyphs should not expand to 2
cells; before fixing that the heavy bracket would align differently
depending on if it had whitespace after it, which was obviously wrong
and looked terrible.

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 -
+            const available_width =
-                self.pad_left * cell_width -
+                cell_width * @as(f64, @floatFromInt(
-                self.pad_right * cell_width;
+                    @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,
@@ -24,24 +25,29 @@ 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,
             .pad_right = 0.1,
-            .pad_top = 0.01,
+            .pad_top = 0.1,
-            .pad_bottom = 0.01,
+            .pad_bottom = 0.1,
         },
         0x276c...0x2771,
         => .{
             .size_horizontal = .cover,
             .size_vertical = .fit,
+            .max_constraint_width = 1,
             .align_horizontal = .center,
             .align_vertical = .center,
+            .pad_top = 0.3,
+            .pad_bottom = 0.3,
         },
         0xe0b0,
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
             .pad_left = -0.06,
@@ -54,6 +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,
@@ -62,6 +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,
@@ -74,6 +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,
@@ -82,6 +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,
@@ -94,6 +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,
@@ -102,6 +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,
@@ -114,6 +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,
@@ -123,6 +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,
@@ -135,6 +149,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .start,
             .align_vertical = .center,
         },
@@ -143,6 +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,
@@ -155,6 +171,7 @@ pub fn getConstraint(cp: u21) Constraint {
         => .{
             .size_horizontal = .stretch,
             .size_vertical = .stretch,
+            .max_constraint_width = 1,
             .align_horizontal = .end,
             .align_vertical = .center,
         },
@@ -204,8 +221,8 @@ pub fn getConstraint(cp: u21) Constraint {
             .align_vertical = .center,
             .pad_left = 0.03,
             .pad_right = 0.03,
-            .pad_top = 0.01,
+            .pad_top = 0.03,
-            .pad_bottom = 0.01,
+            .pad_bottom = 0.03,
             .max_xy_ratio = 0.86,
         },
         0xe0c5,
@@ -216,8 +233,8 @@ pub fn getConstraint(cp: u21) Constraint {
             .align_vertical = .center,
             .pad_left = 0.03,
             .pad_right = 0.03,
-            .pad_top = 0.01,
+            .pad_top = 0.03,
-            .pad_bottom = 0.01,
+            .pad_bottom = 0.03,
             .max_xy_ratio = 0.86,
         },
         0xe0c6,
@@ -228,8 +245,8 @@ pub fn getConstraint(cp: u21) Constraint {
             .align_vertical = .center,
             .pad_left = 0.03,
             .pad_right = 0.03,
-            .pad_top = 0.01,
+            .pad_top = 0.03,
-            .pad_bottom = 0.01,
+            .pad_bottom = 0.03,
             .max_xy_ratio = 0.78,
         },
         0xe0c7,
@@ -240,8 +257,8 @@ pub fn getConstraint(cp: u21) Constraint {
             .align_vertical = .center,
             .pad_left = 0.03,
             .pad_right = 0.03,
-            .pad_top = 0.01,
+            .pad_top = 0.03,
-            .pad_bottom = 0.01,
+            .pad_bottom = 0.03,
             .max_xy_ratio = 0.78,
         },
         0xe0cc,
@@ -285,6 +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,
@@ -297,6 +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,
@@ -309,6 +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,
@@ -321,6 +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

@@ -6,13 +6,15 @@ attributes and scaling rules.
 
 This does include an `eval` call! This is spooky, but we trust the nerd fonts code to
 be safe and not malicious or anything.
+
+This script requires Python 3.12 or greater.
 """
 
 import ast
 import math
-import sys
 from collections import defaultdict
 from contextlib import suppress
+from pathlib import Path
 from types import SimpleNamespace
 from typing import Literal, TypedDict, cast
 
@@ -188,18 +190,31 @@ 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:
         s += f"            .align_vertical = {valign},\n"
 
+    # `overlap` and `ypadding` are mutually exclusive,
+    # this is asserted in the nerd fonts patcher itself.
     if overlap:
         pad = -overlap
         s += f"            .pad_left = {pad},\n"
         s += f"            .pad_right = {pad},\n"
-        v_pad = y_padding - math.copysign(min(0.01, abs(overlap)), overlap)
+        # In the nerd fonts patcher, overlap values
+        # are capped at 0.01 in the vertical direction.
+        v_pad = -min(0.01, overlap)
         s += f"            .pad_top = {v_pad},\n"
         s += f"            .pad_bottom = {v_pad},\n"
+    elif y_padding:
+        s += f"            .pad_top = {y_padding},\n"
+        s += f"            .pad_bottom = {y_padding},\n"
 
     if xy_ratio > 0:
         s += f"            .max_xy_ratio = {xy_ratio},\n"
@@ -236,9 +251,16 @@ def generate_zig_switch_arms(patch_sets: list[PatchSet]) -> str:
 
 
 if __name__ == "__main__":
-    source = sys.stdin.read()
+    project_root = Path(__file__).resolve().parents[2]
+
+    patcher_path = project_root / "vendor" / "nerd-fonts" / "font-patcher.py"
+    source = patcher_path.read_text(encoding="utf-8")
     patch_set = extract_patch_set_values(source)
-    print("""//! This is a generated file, produced by nerd_font_codegen.py
+
+    out_path = project_root / "src" / "font" / "nerd_font_attributes.zig"
+
+    with out_path.open("w", encoding="utf-8") as f:
+        f.write("""//! This is a generated file, produced by nerd_font_codegen.py
 //! DO NOT EDIT BY HAND!
 //!
 //! This file provides info extracted from the nerd fonts patcher script,
@@ -248,6 +270,7 @@ const Constraint = @import("face.zig").RenderOptions.Constraint;
 
 /// Get the a constraints for the provided codepoint.
 pub fn getConstraint(cp: u21) Constraint {
-    return switch (cp) {""")
+    return switch (cp) {
-    print(generate_zig_switch_arms(patch_set))
+""")
-    print("        else => .none,\n    };\n}")
+        f.write(generate_zig_switch_arms(patch_set))
+        f.write("\n        else => .none,\n    };\n}\n")