rearrange box rendering to prepare for more sprite drawing

src/Window.zig

@@ -290,7 +290,7 @@ pub fn create(alloc: Allocator, app: *App, config: *const Config) !*Window {
     const cell_size = try renderer.CellSize.init(alloc, font_group);
 
     // Setup our box font
-    font_group.group.box_font = font.BoxFont{
+    font_group.group.sprite = font.sprite.Face{
         .width = @floatToInt(u32, cell_size.width),
         .height = @floatToInt(u32, cell_size.height),
         .thickness = 2,

src/font/Group.zig

@@ -50,10 +50,11 @@ faces: StyleArray,
 /// the codepoint. This can be set after initialization.
 discover: ?font.Discover = null,
 
-/// Set this to a non-null value to enable box font glyph drawing. If this
+/// Set this to a non-null value to enable sprite glyph drawing. If this
 /// isn't enabled we'll just fall through to trying to use regular fonts
-/// to render box glyphs.
-box_font: ?font.BoxFont = null,
+/// to render sprite glyphs. But more than likely, if this isn't set then
+/// terminal rendering will look wrong.
+sprite: ?font.sprite.Face = null,
 
 pub fn init(
     alloc: Allocator,
@@ -129,8 +130,8 @@ pub const FontIndex = packed struct {
         // We start all special fonts at this index so they can be detected.
         pub const start = std.math.maxInt(IndexInt);
 
-        /// Box drawing, this is rendered JIT using 2D graphics APIs.
-        box = start,
+        /// Sprite drawing, this is rendered JIT using 2D graphics APIs.
+        sprite = start,
     };
 
     style: Style = .regular,
@@ -178,50 +179,11 @@ pub fn indexForCodepoint(
     style: Style,
     p: ?Presentation,
 ) ?FontIndex {
-    // If this is a box drawing glyph, we use the special font index. This
-    // will force special logic where we'll render this ourselves. If we don't
-    // have a box font set, then we just try to use regular fonts.
-    if (self.box_font != null) {
-        if (switch (cp) {
-            // "Box Drawing" block
-            0x2500...0x257F => true,
-
-            // "Block Elements" block
-            0x2580...0x259f => true,
-
-            // "Braille" block
-            0x2800...0x28FF => true,
-
-            // "Symbols for Legacy Computing" block
-            0x1FB00...0x1FB3B => true,
-
-            0x1FB3C...0x1FB40,
-            0x1FB47...0x1FB4B,
-            0x1FB57...0x1FB5B,
-            0x1FB62...0x1FB66,
-            0x1FB6C...0x1FB6F,
-            => true,
-
-            0x1FB41...0x1FB45,
-            0x1FB4C...0x1FB50,
-            0x1FB52...0x1FB56,
-            0x1FB5D...0x1FB61,
-            0x1FB68...0x1FB6B,
-            => true,
-
-            0x1FB46,
-            0x1FB51,
-            0x1FB5C,
-            0x1FB67,
-            0x1FB9A,
-            0x1FB9B,
-            => true,
-
-            0x1FB70...0x1FB8B => true,
-
-            else => false,
-        }) {
-            return FontIndex.initSpecial(.box);
+    // If we have sprite drawing enabled, check if our sprite face can
+    // handle this.
+    if (self.sprite) |sprite| {
+        if (sprite.hasCodepoint(cp, p)) {
+            return FontIndex.initSpecial(.sprite);
         }
     }
 
@@ -275,7 +237,7 @@ fn indexForCodepointExact(self: Group, cp: u32, style: Style, p: ?Presentation)
 /// determining what atlas is needed.
 pub fn presentationFromIndex(self: Group, index: FontIndex) !font.Presentation {
     if (index.special()) |sp| switch (sp) {
-        .box => return .text,
+        .sprite => return .text,
     };
 
     const face = try self.faceFromIndex(index);
@@ -312,7 +274,7 @@ pub fn renderGlyph(
 ) !Glyph {
     // Special-case fonts are rendered directly.
     if (index.special()) |sp| switch (sp) {
-        .box => return try self.box_font.?.renderGlyph(
+        .sprite => return try self.sprite.?.renderGlyph(
             alloc,
             atlas,
             glyph_index,
@@ -402,12 +364,12 @@ test "box glyph" {
     defer group.deinit();
 
     // Set box font
-    group.box_font = font.BoxFont{ .width = 18, .height = 36, .thickness = 2 };
+    group.sprite = font.sprite.Face{ .width = 18, .height = 36, .thickness = 2 };
 
     // Should find a box glyph
     const idx = group.indexForCodepoint(0x2500, .regular, null).?;
     try testing.expectEqual(Style.regular, idx.style);
-    try testing.expectEqual(@enumToInt(FontIndex.Special.box), idx.idx);
+    try testing.expectEqual(@enumToInt(FontIndex.Special.sprite), idx.idx);
 
     // Should render it
     const glyph = try group.renderGlyph(

src/font/Shaper.zig

@@ -582,7 +582,7 @@ test "shape box glyphs" {
     defer testdata.deinit();
 
     // Setup the box font
-    testdata.cache.group.box_font = font.BoxFont{
+    testdata.cache.group.sprite = font.sprite.Face{
         .width = 18,
         .height = 36,
         .thickness = 2,

src/font/main.zig

@@ -1,7 +1,6 @@
 const std = @import("std");
 const build_options = @import("build_options");
 
-pub const BoxFont = @import("BoxFont.zig");
 pub const discovery = @import("discovery.zig");
 pub const face = @import("face.zig");
 pub const DeferredFace = @import("DeferredFace.zig");
@@ -11,6 +10,7 @@ pub const GroupCache = @import("GroupCache.zig");
 pub const Glyph = @import("Glyph.zig");
 pub const Library = @import("Library.zig");
 pub const Shaper = @import("Shaper.zig");
+pub const sprite = @import("sprite.zig");
 pub const Descriptor = discovery.Descriptor;
 pub const Discover = discovery.Discover;
 

src/font/sprite.zig

@@ -0,0 +1,27 @@
+const std = @import("std");
+pub const Face = @import("sprite/Face.zig");
+
+/// Sprites are represented as special codepoints outside of the Unicode
+/// codepoint range. Unicode maxes out at U+10FFFF (21 bits), and we use the
+/// high 11 bits to hide our special characters.
+///
+/// These characters are ONLY used for rendering and NEVER used written to
+/// text files or any other exported format, so we don't use the Private Use
+/// Area of Unicode.
+pub const Sprite = enum(u32) {
+    // Start 1 above the maximum Unicode codepoint.
+    const start: u32 = std.math.maxInt(u21) + 1;
+    const end: u32 = std.math.maxInt(u32);
+
+    underline = start,
+
+    // Note: we don't currently put the box drawing glyphs in here because
+    // there are a LOT and I'm lazy. What I want to do is spend more time
+    // studying the patterns to see if we can programmatically build our
+    // enum perhaps and comptime generate the drawing code at the same time.
+    // I'm not sure if that's advisable yet though.
+};
+
+test {
+    @import("std").testing.refAllDecls(@This());
+}

src/font/sprite/Face.zig

@@ -0,0 +1,96 @@
+//! This implements the built-in "sprite face". This font renders
+//! the built-in glyphs for the terminal, such as box drawing fonts, as well
+//! as specific sprites that are part of our rendering model such as
+//! text decorations (underlines).
+//!
+//! This isn't really a "font face" so much as it is quacks like a font
+//! face with regards to how it works with font.Group. We don't use any
+//! dynamic dispatch so it isn't truly an interface but the functions
+//! and behaviors are close enough to a system face that it makes it easy
+//! to integrate with font.Group. This is desirable so that higher level
+//! processes such as GroupCache, Shaper, etc. don't need to be aware of
+//! special sprite handling and just treat it like a normal font face.
+const Face = @This();
+
+const std = @import("std");
+const builtin = @import("builtin");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const font = @import("../main.zig");
+const Atlas = @import("../../Atlas.zig");
+const Box = @import("Box.zig");
+
+/// The cell width and height.
+width: u32,
+height: u32,
+
+/// Base thickness value for lines of sprites. This is in pixels. If you
+/// want to do any DPI scaling, it is expected to be done earlier.
+thickness: u32,
+
+/// Returns true if the codepoint exists in our sprite font.
+pub fn hasCodepoint(self: Face, cp: u32, p: ?font.Presentation) bool {
+    // We ignore presentation. No matter what presentation is requested
+    // we always provide glyphs for our codepoints.
+    _ = p;
+    _ = self;
+    return Kind.init(cp) != null;
+}
+
+/// Render the glyph.
+pub fn renderGlyph(
+    self: Face,
+    alloc: Allocator,
+    atlas: *Atlas,
+    cp: u32,
+) !font.Glyph {
+    if (std.debug.runtime_safety) assert(self.hasCodepoint(cp, null));
+
+    // Safe to ".?" because of the above assertion.
+    switch (Kind.init(cp).?) {
+        .box => {
+            const f: Box = .{
+                .width = self.width,
+                .height = self.height,
+                .thickness = self.thickness,
+            };
+
+            return try f.renderGlyph(alloc, atlas, cp);
+        },
+    }
+}
+
+/// Kind of sprites we have. Drawing is implemented separately for each kind.
+const Kind = enum {
+    box,
+
+    pub fn init(cp: u32) ?Kind {
+        return switch (cp) {
+            // Box fonts
+            0x2500...0x257F, // "Box Drawing" block
+            0x2580...0x259F, // "Block Elements" block
+            0x2800...0x28FF, // "Braille" block
+            0x1FB00...0x1FB3B, // "Symbols for Legacy Computing" block
+            0x1FB3C...0x1FB40,
+            0x1FB47...0x1FB4B,
+            0x1FB57...0x1FB5B,
+            0x1FB62...0x1FB66,
+            0x1FB6C...0x1FB6F,
+            0x1FB41...0x1FB45,
+            0x1FB4C...0x1FB50,
+            0x1FB52...0x1FB56,
+            0x1FB5D...0x1FB61,
+            0x1FB68...0x1FB6B,
+            0x1FB70...0x1FB8B,
+            0x1FB46,
+            0x1FB51,
+            0x1FB5C,
+            0x1FB67,
+            0x1FB9A,
+            0x1FB9B,
+            => .box,
+
+            else => null,
+        };
+    }
+};

src/renderer/Metal.zig

@@ -409,9 +409,9 @@ pub fn setFontSize(self: *Metal, size: font.face.DesiredSize) !void {
     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);
+    if (self.font_group.group.sprite) |*sprite| {
+        sprite.width = @floatToInt(u32, self.cell_size.width);
+        sprite.height = @floatToInt(u32, self.cell_size.height);
     }
 
     // Notify the window that the cell size changed.

src/renderer/OpenGL.zig

@@ -502,9 +502,9 @@ pub fn setFontSize(self: *OpenGL, size: font.face.DesiredSize) !void {
     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);
+    if (self.font_group.group.sprite) |*sprite| {
+        sprite.width = @floatToInt(u32, self.cell_size.width);
+        sprite.height = @floatToInt(u32, self.cell_size.height);
     }
 
     // Notify the window that the cell size changed.