images: Text filter that draws text with the given options (#9239)

Fixes #9238

resources/images/text.go

@@ -0,0 +1,94 @@
+// Copyright 2021 The Hugo Authors. All rights reserved.
+//
+// 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.
+
+package images
+
+import (
+	"image"
+	"image/draw"
+	"strings"
+
+	"github.com/disintegration/gift"
+
+	"golang.org/x/image/font"
+	"golang.org/x/image/font/gofont/goregular"
+	"golang.org/x/image/font/opentype"
+	"golang.org/x/image/math/fixed"
+)
+
+var _ gift.Filter = (*textFilter)(nil)
+
+type textFilter struct {
+	text, color string
+	x, y        int
+	size        float64
+	linespacing int
+}
+
+func (f textFilter) Draw(dst draw.Image, src image.Image, options *gift.Options) {
+	color, err := hexStringToColor(f.color)
+	if err != nil {
+		panic(err)
+	}
+
+	// Load and parse font
+	ttf := goregular.TTF
+	otf, err := opentype.Parse(ttf)
+	if err != nil {
+		panic(err)
+	}
+
+	// Set font options
+	face, err := opentype.NewFace(otf, &opentype.FaceOptions{
+		Size:    f.size,
+		DPI:     72,
+		Hinting: font.HintingNone,
+	})
+	if err != nil {
+		panic(err)
+	}
+
+	d := font.Drawer{
+		Dst:  dst,
+		Src:  image.NewUniform(color),
+		Face: face,
+	}
+
+	gift.New().Draw(dst, src)
+
+	// Draw text, consider and include linebreaks
+	maxWidth := dst.Bounds().Dx() - 20
+	fontHeight := face.Metrics().Ascent.Ceil()
+
+	// Correct y position based on font and size
+	f.y = f.y + fontHeight
+
+	// Start position
+	y := f.y
+	d.Dot = fixed.P(f.x, f.y)
+
+	// Draw text and break line at max width
+	parts := strings.Fields(f.text)
+	for _, str := range parts {
+		strWith := font.MeasureString(face, str)
+		if (d.Dot.X.Ceil() + strWith.Ceil()) >= maxWidth {
+			y = y + fontHeight + f.linespacing
+			d.Dot = fixed.P(f.x, y)
+		}
+		d.DrawString(str + " ")
+	}
+}
+
+func (f textFilter) Bounds(srcBounds image.Rectangle) image.Rectangle {
+	return image.Rect(0, 0, srcBounds.Dx(), srcBounds.Dy())
+}