text: fix 32-bit glyph id packing

This commit fixes a problem in the unpacking of text.GlyphID on 32 bit architectures.
Incorrectly casting to an `int` on those platforms resulted in truncating the faceIndex
to always be zero. To catch mistakes like this in the future, I've added tests for this
problem that should be run by our new 32-bit CI testing.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

text/gotext_test.go

@@ -1,11 +1,14 @@
 package text
 
 import (
+	"fmt"
 	"math"
 	"reflect"
+	"strconv"
 	"testing"
 
 	nsareg "eliasnaur.com/font/noto/sans/arabic/regular"
+	"github.com/go-text/typesetting/font"
 	"github.com/go-text/typesetting/shaping"
 	"golang.org/x/image/font/gofont/goregular"
 	"golang.org/x/image/math/fixed"
@@ -740,3 +743,50 @@ func TestClosestFontByWeight(t *testing.T) {
 		}
 	}
 }
+
+func TestGlyphIDPacking(t *testing.T) {
+	const maxPPem = fixed.Int26_6((1 << sizebits) - 1)
+	type testcase struct {
+		name      string
+		ppem      fixed.Int26_6
+		faceIndex int
+		gid       font.GID
+		expected  GlyphID
+	}
+	for _, tc := range []testcase{
+		{
+			name: "zero value",
+		},
+		{
+			name:      "10 ppem faceIdx 1 GID 5",
+			ppem:      fixed.I(10),
+			faceIndex: 1,
+			gid:       5,
+			expected:  284223755780101,
+		},
+		{
+			name:      maxPPem.String() + " ppem faceIdx " + strconv.Itoa(math.MaxUint16) + " GID " + fmt.Sprintf("%d", int64(math.MaxUint32)),
+			ppem:      maxPPem,
+			faceIndex: math.MaxUint16,
+			gid:       math.MaxUint32,
+			expected:  18446744073709551615,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			actual := newGlyphID(tc.ppem, tc.faceIndex, tc.gid)
+			if actual != tc.expected {
+				t.Errorf("expected %d, got %d", tc.expected, actual)
+			}
+			actualPPEM, actualFaceIdx, actualGID := splitGlyphID(actual)
+			if actualPPEM != tc.ppem {
+				t.Errorf("expected ppem %d, got %d", tc.ppem, actualPPEM)
+			}
+			if actualFaceIdx != tc.faceIndex {
+				t.Errorf("expected faceIdx %d, got %d", tc.faceIndex, actualFaceIdx)
+			}
+			if actualGID != tc.gid {
+				t.Errorf("expected gid %d, got %d", tc.gid, actualGID)
+			}
+		})
+	}
+}

text/shaper.go

@@ -4,7 +4,6 @@ package text
 
 import (
 	"bufio"
-	"fmt"
 	"io"
 	"strings"
 	"unicode/utf8"
@@ -471,7 +470,6 @@ const (
 // newGlyphID encodes a face and a glyph id into a GlyphID.
 func newGlyphID(ppem fixed.Int26_6, faceIdx int, gid font.GID) GlyphID {
 	if gid&^((1<<gidbits)-1) != 0 {
-		fmt.Println(gid)
 		panic("glyph id out of bounds")
 	}
 	if faceIdx&^((1<<facebits)-1) != 0 {
@@ -488,7 +486,7 @@ func newGlyphID(ppem fixed.Int26_6, faceIdx int, gid font.GID) GlyphID {
 
 // splitGlyphID is the opposite of newGlyphID.
 func splitGlyphID(g GlyphID) (fixed.Int26_6, int, font.GID) {
-	faceIdx := int(g) >> (gidbits + sizebits)
+	faceIdx := int(uint64(g) >> (gidbits + sizebits))
 	ppem := fixed.Int26_6((g & ((1<<sizebits - 1) << gidbits)) >> gidbits)
 	gid := font.GID(g) & (1<<gidbits - 1)
 	return ppem, faceIdx, gid