text/v2: add Metrics.XHeight and Metrics.CapHeight

Closes #3082

text/v2/gotext.go

@@ -201,6 +201,21 @@ func (g *GoTextFace) Metrics() Metrics {
 		m.VDescent = float64(-v.Descender) * scale
 	}
 
+	m.XHeight = float64(g.Source.f.LineMetric(font.XHeight)) * scale
+	m.CapHeight = float64(g.Source.f.LineMetric(font.CapHeight)) * scale
+
+	// XHeight and CapHeight might not be correct for some old fonts (go-text/typesetting#169).
+	if m.XHeight <= 0 {
+		if _, gs := g.Source.shape("x", g); len(gs) > 0 {
+			m.XHeight = fixed26_6ToFloat64(-gs[0].bounds.Min.Y)
+		}
+	}
+	if m.CapHeight <= 0 {
+		if _, gs := g.Source.shape("H", g); len(gs) > 0 {
+			m.CapHeight = fixed26_6ToFloat64(-gs[0].bounds.Min.Y)
+		}
+	}
+
 	return m
 }
 

text/v2/gox.go

@@ -45,6 +45,8 @@ type GoXFace struct {
 
 	glyphImageCache glyphImageCache[goXFaceGlyphImageCacheKey]
 
+	cachedMetrics Metrics
+
 	addr *GoXFace
 }
 
@@ -69,12 +71,28 @@ func (s *GoXFace) copyCheck() {
 func (s *GoXFace) Metrics() Metrics {
 	s.copyCheck()
 
-	m := s.f.Metrics()
+	if s.cachedMetrics != (Metrics{}) {
-	return Metrics{
+		return s.cachedMetrics
-		HLineGap: fixed26_6ToFloat64(m.Height - m.Ascent - m.Descent),
-		HAscent:  fixed26_6ToFloat64(m.Ascent),
-		HDescent: fixed26_6ToFloat64(m.Descent),
 	}
+
+	fm := s.f.Metrics()
+	m := Metrics{
+		HLineGap:  fixed26_6ToFloat64(fm.Height - fm.Ascent - fm.Descent),
+		HAscent:   fixed26_6ToFloat64(fm.Ascent),
+		HDescent:  fixed26_6ToFloat64(fm.Descent),
+		XHeight:   fixed26_6ToFloat64(fm.XHeight),
+		CapHeight: fixed26_6ToFloat64(fm.CapHeight),
+	}
+
+	// There is an issue that XHeight is negative for some old fonts (golang/go#69378).
+	if fm.XHeight < 0 {
+		m.XHeight *= -1
+	}
+	if fm.CapHeight < 0 {
+		m.CapHeight *= -1
+	}
+	s.cachedMetrics = m
+	return m
 }
 
 // UnsafeInternal returns its internal font.Face.

text/v2/multi.go

@@ -75,6 +75,12 @@ func (m *MultiFace) Metrics() Metrics {
 		if mt1.VDescent > mt.VDescent {
 			mt.VDescent = mt1.VDescent
 		}
+		if mt1.XHeight > mt.XHeight {
+			mt.XHeight = mt1.XHeight
+		}
+		if mt1.CapHeight > mt.CapHeight {
+			mt.CapHeight = mt1.CapHeight
+		}
 	}
 	return mt
 }

text/v2/testdata/LICENSE.md

@@ -0,0 +1,310 @@
+# Licenses
+
+## `MPLUS1p-Regular.ttf`
+
+https://fonts.google.com/specimen/M+PLUS+1p
+
+```
+Copyright 2016 The M+ Project Authors.
+
+This Font Software is licensed under the SIL Open Font License, Version 1.1.
+This license is copied below, and is also available with a FAQ at:
+https://openfontlicense.org
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded,
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
+contains the above copyright notice and this license. These can be
+included either as stand-alone text files, human-readable headers or
+in the appropriate machine-readable metadata fields within text or
+binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+Name(s) unless explicit written permission is granted by the corresponding
+Copyright Holder. This restriction only applies to the primary font name as
+presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
+Modified Version, except to acknowledge the contribution(s) of the
+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
+OTHER DEALINGS IN THE FONT SOFTWARE.
+```
+
+## `Roboto-Regular.ttf`
+
+https://fonts.google.com/specimen/Roboto
+
+
+```
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
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+
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+      designated in writing by the copyright owner as "Not a Contribution."
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+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
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+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
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+   6. Trademarks. This License does not grant permission to use the trade
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+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
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+      on Your own behalf and on Your sole responsibility, not on behalf
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+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
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+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
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+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+```

text/v2/text.go

@@ -69,6 +69,12 @@ type Metrics struct {
 	// VDescent is the distance in pixels from the top of a line to its baseline for vertical lines.
 	// If the face is GoXFace or the font doesn't support a vertical direction, VDescent is 0.
 	VDescent float64
+
+	// XHeight is the distance in pixels from the baseline to the top of the lower case letters.
+	XHeight float64
+
+	// CapHeight is the distance in pixels from the baseline to the top of the capital letters.
+	CapHeight float64
 }
 
 func fixed26_6ToFloat32(x fixed.Int26_6) float32 {

text/v2/text_test.go

@@ -15,14 +15,19 @@
 package text_test
 
 import (
+	"bytes"
 	"image"
 	"image/color"
+	"math"
+	"os"
+	"path/filepath"
 	"regexp"
 	"strings"
 	"testing"
 
 	"github.com/hajimehoshi/bitmapfont/v3"
 	"golang.org/x/image/font"
+	"golang.org/x/image/font/opentype"
 	"golang.org/x/image/math/fixed"
 
 	"github.com/hajimehoshi/ebiten/v2"
@@ -371,3 +376,75 @@ func TestDrawOptionsNotModified(t *testing.T) {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
 }
+
+func TestGoXFaceMetrics(t *testing.T) {
+	const size = 100
+
+	fontFiles := []string{
+		// MPLUS1p-Regular.ttf is an old version of M+ 1p font, and this doesn't have metadata.
+		"MPLUS1p-Regular.ttf",
+		"Roboto-Regular.ttf",
+	}
+
+	for _, fontFile := range fontFiles {
+		fontFile := fontFile
+		t.Run(fontFile, func(t *testing.T) {
+			fontdata, err := os.ReadFile(filepath.Join("testdata", fontFile))
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			sfntFont, err := opentype.Parse(fontdata)
+			if err != nil {
+				t.Fatal(err)
+			}
+			opentypeFace, err := opentype.NewFace(sfntFont, &opentype.FaceOptions{
+				Size: size,
+				DPI:  72,
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			goXFace := text.NewGoXFace(opentypeFace)
+			goXMetrics := goXFace.Metrics()
+			if goXMetrics.XHeight <= 0 {
+				t.Errorf("GoXFace's XHeight must be positive but not: %f", goXMetrics.XHeight)
+			}
+			if goXMetrics.CapHeight <= 0 {
+				t.Errorf("GoXFace's CapHeight must be positive but not: %f", goXMetrics.CapHeight)
+			}
+
+			goTextFaceSource, err := text.NewGoTextFaceSource(bytes.NewBuffer(fontdata))
+			if err != nil {
+				t.Fatal(err)
+			}
+			goTextFace := &text.GoTextFace{
+				Source: goTextFaceSource,
+				Size:   size,
+			}
+			goTextMetrics := goTextFace.Metrics()
+			if goTextMetrics.XHeight <= 0 {
+				t.Errorf("GoTextFace's XHeight must be positive but not: %f", goTextMetrics.XHeight)
+			}
+			if goTextMetrics.CapHeight <= 0 {
+				t.Errorf("GoTextFace's CapHeight must be positive but not: %f", goTextMetrics.CapHeight)
+			}
+
+			if math.Abs(goXMetrics.XHeight-goTextMetrics.XHeight) >= 0.1 {
+				t.Errorf("XHeight values don't match: %f (GoXFace) vs %f (GoTextFace)", goXMetrics.XHeight, goTextMetrics.XHeight)
+			}
+			if math.Abs(goXMetrics.CapHeight-goTextMetrics.CapHeight) >= 0.1 {
+				t.Errorf("CapHeight values don't match: %f (GoXFace) vs %f (GoTextFace)", goXMetrics.CapHeight, goTextMetrics.CapHeight)
+			}
+
+			// Check that a MultiFace should have the same metrics.
+			multiFace, err := text.NewMultiFace(goTextFace)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got := multiFace.Metrics(); got != goTextMetrics {
+				t.Errorf("got: %v, want: %v", got, goTextMetrics)
+			}
+		})
+	}
+}