Draw image/text with current transformation appied

context.go

@@ -4,14 +4,15 @@ package gg
 import (
 	"image"
 	"image/color"
-	"image/draw"
 	"image/png"
 	"io"
 	"math"
 
 	"github.com/golang/freetype/raster"
+	"golang.org/x/image/draw"
 	"golang.org/x/image/font"
 	"golang.org/x/image/font/basicfont"
+	"golang.org/x/image/math/f64"
 )
 
 type LineCap int
@@ -566,7 +567,6 @@ func (dc *Context) DrawRegularPolygon(n int, x, y, r, rotation float64) {
 }
 
 // DrawImage draws the specified image at the specified point.
-// Currently, rotation and scaling transforms are not supported.
 func (dc *Context) DrawImage(im image.Image, x, y int) {
 	dc.DrawImageAnchored(im, x, y, 0, 0)
 }
@@ -578,12 +578,17 @@ func (dc *Context) DrawImageAnchored(im image.Image, x, y int, ax, ay float64) {
 	s := im.Bounds().Size()
 	x -= int(ax * float64(s.X))
 	y -= int(ay * float64(s.Y))
-	p := image.Pt(x, y)
-	r := image.Rectangle{p, p.Add(s)}
+	transformer := draw.BiLinear
+	fx, fy := float64(x), float64(y)
+	m := dc.matrix.Translate(fx, fy)
+	s2d := f64.Aff3{m.XX, m.XY, m.X0, m.YX, m.YY, m.Y0}
 	if dc.mask == nil {
-		draw.Draw(dc.im, r, im, image.ZP, draw.Over)
+		transformer.Transform(dc.im, s2d, im, im.Bounds(), draw.Over, nil)
 	} else {
-		draw.DrawMask(dc.im, r, im, image.ZP, dc.mask, p, draw.Over)
+		transformer.Transform(dc.im, s2d, im, im.Bounds(), draw.Over, &draw.Options{
+			DstMask:  dc.mask,
+			DstMaskP: image.ZP,
+		})
 	}
 }
 
@@ -609,11 +614,34 @@ func (dc *Context) drawString(im *image.RGBA, s string, x, y float64) {
 		Face: dc.fontFace,
 		Dot:  fixp(x, y),
 	}
-	d.DrawString(s)
+	// based on Drawer.DrawString() in golang.org/x/image/font/font.go
+	prevC := rune(-1)
+	for _, c := range s {
+		if prevC >= 0 {
+			d.Dot.X += d.Face.Kern(prevC, c)
+		}
+		dr, mask, maskp, advance, ok := d.Face.Glyph(d.Dot, c)
+		if !ok {
+			// TODO: is falling back on the U+FFFD glyph the responsibility of
+			// the Drawer or the Face?
+			// TODO: set prevC = '\ufffd'?
+			continue
+		}
+		sr := dr.Sub(dr.Min)
+		transformer := draw.BiLinear
+		fx, fy := float64(dr.Min.X), float64(dr.Min.Y)
+		m := dc.matrix.Translate(fx, fy)
+		s2d := f64.Aff3{m.XX, m.XY, m.X0, m.YX, m.YY, m.Y0}
+		transformer.Transform(d.Dst, s2d, d.Src, sr, draw.Over, &draw.Options{
+			SrcMask:  mask,
+			SrcMaskP: maskp,
+		})
+		d.Dot.X += advance
+		prevC = c
+	}
 }
 
 // DrawString draws the specified text at the specified point.
-// Currently, rotation and scaling transforms are not supported.
 func (dc *Context) DrawString(s string, x, y float64) {
 	dc.DrawStringAnchored(s, x, y, 0, 0)
 }
@@ -623,7 +651,6 @@ func (dc *Context) DrawString(s string, x, y float64) {
 // text. Use ax=0.5, ay=0.5 to center the text at the specified point.
 func (dc *Context) DrawStringAnchored(s string, x, y, ax, ay float64) {
 	w, h := dc.MeasureString(s)
-	x, y = dc.TransformPoint(x, y)
 	x -= ax * w
 	y += ay * h
 	if dc.mask == nil {

examples/rotated-image.go

@@ -0,0 +1,34 @@
+package main
+
+import "github.com/fogleman/gg"
+
+func main() {
+	const W = 400
+	const H = 500
+	im, err := gg.LoadPNG("examples/gopher.png")
+	if err != nil {
+		panic(err)
+	}
+	iw, ih := im.Bounds().Dx(), im.Bounds().Dy()
+	dc := gg.NewContext(W, H)
+	// draw outline
+	dc.SetHexColor("#ff0000")
+	dc.SetLineWidth(1)
+	dc.DrawRectangle(0, 0, float64(W), float64(H))
+	dc.Stroke()
+	// draw full image
+	dc.SetHexColor("#0000ff")
+	dc.SetLineWidth(2)
+	dc.DrawRectangle(100, 210, float64(iw), float64(ih))
+	dc.Stroke()
+	dc.DrawImage(im, 100, 210)
+	// draw image with current matrix applied
+	dc.SetHexColor("#0000ff")
+	dc.SetLineWidth(2)
+	dc.Rotate(gg.Radians(10))
+	dc.DrawRectangle(100, 0, float64(iw), float64(ih)/2+20.0)
+	dc.StrokePreserve()
+	dc.Clip()
+	dc.DrawImageAnchored(im, 100, 0, 0.0, 0.0)
+	dc.SavePNG("out.png")
+}

examples/rotated-text.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"github.com/fogleman/gg"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/font/gofont/goregular"
+)
+
+func main() {
+	const S = 400
+	dc := gg.NewContext(S, S)
+	dc.SetRGB(1, 1, 1)
+	dc.Clear()
+	dc.SetRGB(0, 0, 0)
+	font, err := truetype.Parse(goregular.TTF)
+	if err != nil {
+		panic("")
+	}
+	face := truetype.NewFace(font, &truetype.Options{
+		Size: 40,
+	})
+	dc.SetFontFace(face)
+	text := "Hello, world!"
+	w, h := dc.MeasureString(text)
+	dc.Rotate(gg.Radians(10))
+	dc.DrawRectangle(100, 180, w, h)
+	dc.Stroke()
+	dc.DrawStringAnchored(text, 100, 180, 0.0, 0.0)
+	dc.SavePNG("out.png")
+}