word wrap in progress

context.go

@@ -504,6 +504,14 @@ func (dc *Context) DrawStringAnchored(s string, x, y, ax, ay float64) {
 	d.DrawString(s)
 }
 
+func (dc *Context) DrawStringWrapped(s string, x, y, w float64) {
+	lines := wordWrap(dc, s, w)
+	for _, line := range lines {
+		dc.DrawStringAnchored(line, x, y, 0, 0)
+		y += dc.fontHeight * 1.5
+	}
+}
+
 // MeasureString returns the rendered width and height of the specified text
 // given the current font face.
 func (dc *Context) MeasureString(s string) (w, h float64) {

examples/lorem.go

@@ -2,14 +2,12 @@ package main
 
 import "github.com/fogleman/gg"
 
-var lines = []string{
+var line = ("Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod" +
-	"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod",
+	"tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam," +
-	"tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,",
+	"quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo" +
-	"quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo",
+	"consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse" +
-	"consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse",
+	"cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat" +
-	"cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat",
+	"non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. ")
-	"non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.",
-}
 
 func main() {
 	const W = 800
@@ -18,11 +16,7 @@ func main() {
 	dc.SetRGB(1, 1, 1)
 	dc.Clear()
 	dc.SetRGB(0, 0, 0)
-	// dc.LoadFontFace("/Library/Fonts/Arial.ttf", 18)
+	dc.LoadFontFace("/Library/Fonts/Arial.ttf", 18)
-	const h = 24
+	dc.DrawStringWrapped(line, 20, 20, W-40)
-	for i, line := range lines {
-		y := H/2 - h*len(lines)/2 + i*h
-		dc.DrawStringAnchored(line, 400, float64(y), 0.5, 0.5)
-	}
 	dc.SavePNG("out.png")
 }

wrap.go

@@ -0,0 +1,61 @@
+package gg
+
+import (
+	"strings"
+	"unicode"
+)
+
+type measureStringer interface {
+	MeasureString(s string) (w, h float64)
+}
+
+func splitOnSpace(x string) []string {
+	var result []string
+	pi := 0
+	ps := false
+	for i, c := range x {
+		s := unicode.IsSpace(c)
+		if s != ps && i > 0 {
+			result = append(result, x[pi:i])
+			pi = i
+		}
+		ps = s
+	}
+	result = append(result, x[pi:])
+	return result
+}
+
+func wordWrap(m measureStringer, s string, width float64) []string {
+	var result []string
+	for _, line := range strings.Split(s, "\n") {
+		fields := splitOnSpace(line)
+		widths := make([]float64, len(fields))
+		for i, field := range fields {
+			widths[i], _ = m.MeasureString(field)
+		}
+		start := 0
+		total := 0.0
+		for i := 0; i < len(fields); i += 2 {
+			if total+widths[i] > width {
+				if i == start {
+					end := i + 2
+					result = append(result, strings.Join(fields[start:end], ""))
+					start, total = end, 0
+					continue
+				} else {
+					end := i
+					result = append(result, strings.Join(fields[start:end], ""))
+					start, total = end, 0
+				}
+			}
+			total += widths[i] + widths[i+1]
+		}
+		if start < len(fields) {
+			result = append(result, strings.Join(fields[start:], ""))
+		}
+	}
+	for i, line := range result {
+		result[i] = strings.TrimSpace(line)
+	}
+	return result
+}