anchored functions

README.md

@@ -48,7 +48,9 @@ DrawArc(x, y, r, angle1, angle2 float64)
 DrawEllipse(x, y, rx, ry float64)
 DrawEllipticalArc(x, y, rx, ry, angle1, angle2 float64)
 DrawImage(im image.Image, x, y int)
-DrawString(x, y float64, s string)
+DrawImageAnchored(im image.Image, x, y int, ax, ay float64)
+DrawString(s string, x, y float64)
+DrawStringAnchored(s string, x, y, ax, ay float64)
 
 MoveTo(x, y float64)
 LineTo(x, y float64)

context.go

@@ -323,8 +323,15 @@ func (dc *Context) DrawCircle(x, y, r float64) {
 }
 
 func (dc *Context) DrawImage(im image.Image, x, y int) {
+	dc.DrawImageAnchored(im, x, y, 0, 0)
+}
+
+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(im.Bounds().Size())}
+	r := image.Rectangle{p, p.Add(s)}
 	draw.Draw(dc.im, r, im, image.ZP, draw.Over)
 }
 
@@ -339,7 +346,14 @@ func (dc *Context) LoadFontFace(path string, points float64) {
 	dc.fontHeight = points * 72 / 96
 }
 
-func (dc *Context) DrawString(x, y float64, s string) {
+func (dc *Context) DrawString(s string, x, y float64) {
+	dc.DrawStringAnchored(s, x, y, 0, 0)
+}
+
+func (dc *Context) DrawStringAnchored(s string, x, y, ax, ay float64) {
+	w, h := dc.MeasureString(s)
+	x -= ax * w
+	y += ay * h
 	x, y = dc.TransformPoint(x, y)
 	d := &font.Drawer{
 		Dst:  dc.im,

examples/ellipse.go

@@ -14,9 +14,7 @@ func main() {
 		dc.Pop()
 	}
 	if im, err := gg.LoadPNG("examples/gopher.png"); err == nil {
-		w := im.Bounds().Size().X
+		dc.DrawImageAnchored(im, S/2, S/2, 0.5, 0.5)
-		h := im.Bounds().Size().Y
-		dc.DrawImage(im, S/2-w/2, S/2-h/2)
 	}
 	dc.SavePNG("out.png")
 }

examples/text.go

@@ -1,20 +1,14 @@
 package main
 
-import (
+import "github.com/fogleman/gg"
-	"fmt"
-
-	"github.com/fogleman/gg"
-)
 
 func main() {
-	dc := gg.NewContext(1000, 1000)
+	const S = 1024
+	dc := gg.NewContext(S, S)
 	dc.SetRGB(1, 1, 1)
 	dc.Clear()
 	dc.SetRGB(0, 0, 0)
 	dc.LoadFontFace("/Library/Fonts/Arial.ttf", 96)
-	s := "Hello, world!"
+	dc.DrawStringAnchored("Hello, world!", S/2, S/2, 0.5, 0.5)
-	w, h := dc.MeasureString(s)
-	fmt.Println(w, h)
-	dc.DrawString(500-w/2, 500+h/2, s)
 	dc.SavePNG("out.png")
 }