add Dockerfile

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diff --git a/vendor/github.com/fogleman/gg/.gitignore b/vendor/github.com/fogleman/gg/.gitignore
new file mode 100644
index 0000000..2fa80d6
--- /dev/null
+++ b/vendor/github.com/fogleman/gg/.gitignore
@@ -0,0 +1,2 @@
+*.png
+
diff --git a/vendor/github.com/fogleman/gg/LICENSE.md b/vendor/github.com/fogleman/gg/LICENSE.md
new file mode 100644
index 0000000..d7b4099
--- /dev/null
+++ b/vendor/github.com/fogleman/gg/LICENSE.md
@@ -0,0 +1,19 @@
+Copyright (C) 2016 Michael Fogleman
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/vendor/github.com/fogleman/gg/README.md b/vendor/github.com/fogleman/gg/README.md
new file mode 100644
index 0000000..0417f94
--- /dev/null
+++ b/vendor/github.com/fogleman/gg/README.md
@@ -0,0 +1,216 @@
+# Go Graphics
+
+`gg` is a library for rendering 2D graphics in pure Go.
+
+![Stars](http://i.imgur.com/CylQIJt.png)
+
+## Installation
+
+    go get -u github.com/fogleman/gg
+
+Alternatively, you may use gopkg.in to grab a specific major-version:
+
+    go get -u gopkg.in/fogleman/gg.v1
+
+## Documentation
+
+https://godoc.org/github.com/fogleman/gg
+
+## Hello, Circle!
+
+Look how easy!
+
+```go
+package main
+
+import "github.com/fogleman/gg"
+
+func main() {
+    dc := gg.NewContext(1000, 1000)
+    dc.DrawCircle(500, 500, 400)
+    dc.SetRGB(0, 0, 0)
+    dc.Fill()
+    dc.SavePNG("out.png")
+}
+```
+
+## Examples
+
+There are [lots of examples](https://github.com/fogleman/gg/tree/master/examples) included. They're mostly for testing the code, but they're good for learning, too.
+
+![Examples](http://i.imgur.com/tMFoyzu.png)
+
+## Creating Contexts
+
+There are a few ways of creating a context.
+
+```go
+NewContext(width, height int) *Context
+NewContextForImage(im image.Image) *Context
+NewContextForRGBA(im *image.RGBA) *Context
+```
+
+## Drawing Functions
+
+Ever used a graphics library that didn't have functions for drawing rectangles
+or circles? What a pain!
+
+```go
+DrawPoint(x, y, r float64)
+DrawLine(x1, y1, x2, y2 float64)
+DrawRectangle(x, y, w, h float64)
+DrawRoundedRectangle(x, y, w, h, r float64)
+DrawCircle(x, y, r float64)
+DrawArc(x, y, r, angle1, angle2 float64)
+DrawEllipse(x, y, rx, ry float64)
+DrawEllipticalArc(x, y, rx, ry, angle1, angle2 float64)
+DrawRegularPolygon(n int, x, y, r, rotation float64)
+DrawImage(im image.Image, x, y int)
+DrawImageAnchored(im image.Image, x, y int, ax, ay float64)
+SetPixel(x, y int)
+
+MoveTo(x, y float64)
+LineTo(x, y float64)
+QuadraticTo(x1, y1, x2, y2 float64)
+CubicTo(x1, y1, x2, y2, x3, y3 float64)
+ClosePath()
+ClearPath()
+NewSubPath()
+
+Clear()
+Stroke()
+Fill()
+StrokePreserve()
+FillPreserve()
+```
+
+It is often desired to center an image at a point. Use `DrawImageAnchored` with `ax` and `ay` set to 0.5 to do this. Use 0 to left or top align. Use 1 to right or bottom align. `DrawStringAnchored` does the same for text, so you don't need to call `MeasureString` yourself.
+
+## Text Functions
+
+It will even do word wrap for you!
+
+```go
+DrawString(s string, x, y float64)
+DrawStringAnchored(s string, x, y, ax, ay float64)
+DrawStringWrapped(s string, x, y, ax, ay, width, lineSpacing float64, align Align)
+MeasureString(s string) (w, h float64)
+WordWrap(s string, w float64) []string
+SetFontFace(fontFace font.Face)
+LoadFontFace(path string, points float64) error
+```
+
+## Color Functions
+
+Colors can be set in several different ways for your convenience.
+
+```go
+SetRGB(r, g, b float64)
+SetRGBA(r, g, b, a float64)
+SetRGB255(r, g, b int)
+SetRGBA255(r, g, b, a int)
+SetColor(c color.Color)
+SetHexColor(x string)
+```
+
+## Stroke & Fill Options
+
+```go
+SetLineWidth(lineWidth float64)
+SetLineCap(lineCap LineCap)
+SetLineJoin(lineJoin LineJoin)
+SetDash(dashes ...float64)
+SetFillRule(fillRule FillRule)
+```
+
+## Gradients & Patterns
+
+`gg` supports linear and radial gradients and surface patterns. You can also implement your own patterns.
+
+```go
+SetFillStyle(pattern Pattern)
+SetStrokeStyle(pattern Pattern)
+NewSolidPattern(color color.Color)
+NewLinearGradient(x0, y0, x1, y1 float64)
+NewRadialGradient(x0, y0, r0, x1, y1, r1 float64)
+NewSurfacePattern(im image.Image, op RepeatOp)
+```
+
+## Transformation Functions
+
+```go
+Identity()
+Translate(x, y float64)
+Scale(x, y float64)
+Rotate(angle float64)
+Shear(x, y float64)
+ScaleAbout(sx, sy, x, y float64)
+RotateAbout(angle, x, y float64)
+ShearAbout(sx, sy, x, y float64)
+TransformPoint(x, y float64) (tx, ty float64)
+InvertY()
+```
+
+It is often desired to rotate or scale about a point that is not the origin. The functions `RotateAbout`, `ScaleAbout`, `ShearAbout` are provided as a convenience.
+
+`InvertY` is provided in case Y should increase from bottom to top vs. the default top to bottom.
+
+## Stack Functions
+
+Save and restore the state of the context. These can be nested.
+
+```go
+Push()
+Pop()
+```
+
+## Clipping Functions
+
+Use clipping regions to restrict drawing operations to an area that you
+defined using paths.
+
+```go
+Clip()
+ClipPreserve()
+ResetClip()
+```
+
+## Helper Functions
+
+Sometimes you just don't want to write these yourself.
+
+```go
+Radians(degrees float64) float64
+Degrees(radians float64) float64
+LoadImage(path string) (image.Image, error)
+LoadPNG(path string) (image.Image, error)
+SavePNG(path string, im image.Image) error
+```
+
+![Separator](http://i.imgur.com/fsUvnPB.png)
+
+## Another Example
+
+See the output of this example below.
+
+```go
+package main
+
+import "github.com/fogleman/gg"
+
+func main() {
+	const S = 1024
+	dc := gg.NewContext(S, S)
+	dc.SetRGBA(0, 0, 0, 0.1)
+	for i := 0; i < 360; i += 15 {
+		dc.Push()
+		dc.RotateAbout(gg.Radians(float64(i)), S/2, S/2)
+		dc.DrawEllipse(S/2, S/2, S*7/16, S/8)
+		dc.Fill()
+		dc.Pop()
+	}
+	dc.SavePNG("out.png")
+}
+```
+
+![Ellipses](http://i.imgur.com/J9CBZef.png)
diff --git a/vendor/github.com/fogleman/gg/bezier.go b/vendor/github.com/fogleman/gg/bezier.go
new file mode 100644
index 0000000..f2cd7ab
--- /dev/null
+++ b/vendor/github.com/fogleman/gg/bezier.go
@@ -0,0 +1,59 @@
+package gg
+
+import "math"
+
+func quadratic(x0, y0, x1, y1, x2, y2, t float64) (x, y float64) {
+	u := 1 - t
+	a := u * u
+	b := 2 * u * t
+	c := t * t
+	x = a*x0 + b*x1 + c*x2
+	y = a*y0 + b*y1 + c*y2
+	return
+}
+
+func QuadraticBezier(x0, y0, x1, y1, x2, y2 float64) []Point {
+	l := (math.Hypot(x1-x0, y1-y0) +
+		math.Hypot(x2-x1, y2-y1))
+	n := int(l + 0.5)
+	if n < 4 {
+		n = 4
+	}
+	d := float64(n) - 1
+	result := make([]Point, n)
+	for i := 0; i < n; i++ {
+		t := float64(i) / d
+		x, y := quadratic(x0, y0, x1, y1, x2, y2, t)
+		result[i] = Point{x, y}
+	}
+	return result
+}
+
+func cubic(x0, y0, x1, y1, x2, y2, x3, y3, t float64) (x, y float64) {
+	u := 1 - t
+	a := u * u * u
+	b := 3 * u * u * t
+	c := 3 * u * t * t
+	d := t * t * t
+	x = a*x0 + b*x1 + c*x2 + d*x3
+	y = a*y0 + b*y1 + c*y2 + d*y3
+	return
+}
+
+func CubicBezier(x0, y0, x1, y1, x2, y2, x3, y3 float64) []Point {
+	l := (math.Hypot(x1-x0, y1-y0) +
+		math.Hypot(x2-x1, y2-y1) +
+		math.Hypot(x3-x2, y3-y2))
+	n := int(l + 0.5)
+	if n < 4 {
+		n = 4
+	}
+	d := float64(n) - 1
+	result := make([]Point, n)
+	for i := 0; i < n; i++ {
+		t := float64(i) / d
+		x, y := cubic(x0, y0, x1, y1, x2, y2, x3, y3, t)
+		result[i] = Point{x, y}
+	}
+	return result
+}
diff --git a/vendor/github.com/fogleman/gg/context.go b/vendor/github.com/fogleman/gg/context.go
new file mode 100644
index 0000000..3d973b8
--- /dev/null
+++ b/vendor/github.com/fogleman/gg/context.go
@@ -0,0 +1,824 @@
+// Package gg provides a simple API for rendering 2D graphics in pure Go.
+package gg
+
+import (
+	"errors"
+	"image"
+	"image/color"
+	"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
+
+const (
+	LineCapRound LineCap = iota
+	LineCapButt
+	LineCapSquare
+)
+
+type LineJoin int
+
+const (
+	LineJoinRound LineJoin = iota
+	LineJoinBevel
+)
+
+type FillRule int
+
+const (
+	FillRuleWinding FillRule = iota
+	FillRuleEvenOdd
+)
+
+type Align int
+
+const (
+	AlignLeft Align = iota
+	AlignCenter
+	AlignRight
+)
+
+var (
+	defaultFillStyle   = NewSolidPattern(color.White)
+	defaultStrokeStyle = NewSolidPattern(color.Black)
+)
+
+type Context struct {
+	width         int
+	height        int
+	im            *image.RGBA
+	mask          *image.Alpha
+	color         color.Color
+	fillPattern   Pattern
+	strokePattern Pattern
+	strokePath    raster.Path
+	fillPath      raster.Path
+	start         Point
+	current       Point
+	hasCurrent    bool
+	dashes        []float64
+	lineWidth     float64
+	lineCap       LineCap
+	lineJoin      LineJoin
+	fillRule      FillRule
+	fontFace      font.Face
+	fontHeight    float64
+	matrix        Matrix
+	stack         []*Context
+}
+
+// NewContext creates a new image.RGBA with the specified width and height
+// and prepares a context for rendering onto that image.
+func NewContext(width, height int) *Context {
+	return NewContextForRGBA(image.NewRGBA(image.Rect(0, 0, width, height)))
+}
+
+// NewContextForImage copies the specified image into a new image.RGBA
+// and prepares a context for rendering onto that image.
+func NewContextForImage(im image.Image) *Context {
+	return NewContextForRGBA(imageToRGBA(im))
+}
+
+// NewContextForRGBA prepares a context for rendering onto the specified image.
+// No copy is made.
+func NewContextForRGBA(im *image.RGBA) *Context {
+	return &Context{
+		width:         im.Bounds().Size().X,
+		height:        im.Bounds().Size().Y,
+		im:            im,
+		color:         color.Transparent,
+		fillPattern:   defaultFillStyle,
+		strokePattern: defaultStrokeStyle,
+		lineWidth:     1,
+		fillRule:      FillRuleWinding,
+		fontFace:      basicfont.Face7x13,
+		fontHeight:    13,
+		matrix:        Identity(),
+	}
+}
+
+// Image returns the image that has been drawn by this context.
+func (dc *Context) Image() image.Image {
+	return dc.im
+}
+
+// Width returns the width of the image in pixels.
+func (dc *Context) Width() int {
+	return dc.width
+}
+
+// Height returns the height of the image in pixels.
+func (dc *Context) Height() int {
+	return dc.height
+}
+
+// SavePNG encodes the image as a PNG and writes it to disk.
+func (dc *Context) SavePNG(path string) error {
+	return SavePNG(path, dc.im)
+}
+
+// EncodePNG encodes the image as a PNG and writes it to the provided io.Writer.
+func (dc *Context) EncodePNG(w io.Writer) error {
+	return png.Encode(w, dc.im)
+}
+
+// SetDash sets the current dash pattern to use. Call with zero arguments to
+// disable dashes. The values specify the lengths of each dash, with
+// alternating on and off lengths.
+func (dc *Context) SetDash(dashes ...float64) {
+	dc.dashes = dashes
+}
+
+func (dc *Context) SetLineWidth(lineWidth float64) {
+	dc.lineWidth = lineWidth
+}
+
+func (dc *Context) SetLineCap(lineCap LineCap) {
+	dc.lineCap = lineCap
+}
+
+func (dc *Context) SetLineCapRound() {
+	dc.lineCap = LineCapRound
+}
+
+func (dc *Context) SetLineCapButt() {
+	dc.lineCap = LineCapButt
+}
+
+func (dc *Context) SetLineCapSquare() {
+	dc.lineCap = LineCapSquare
+}
+
+func (dc *Context) SetLineJoin(lineJoin LineJoin) {
+	dc.lineJoin = lineJoin
+}
+
+func (dc *Context) SetLineJoinRound() {
+	dc.lineJoin = LineJoinRound
+}
+
+func (dc *Context) SetLineJoinBevel() {
+	dc.lineJoin = LineJoinBevel
+}
+
+func (dc *Context) SetFillRule(fillRule FillRule) {
+	dc.fillRule = fillRule
+}
+
+func (dc *Context) SetFillRuleWinding() {
+	dc.fillRule = FillRuleWinding
+}
+
+func (dc *Context) SetFillRuleEvenOdd() {
+	dc.fillRule = FillRuleEvenOdd
+}
+
+// Color Setters
+
+func (dc *Context) setFillAndStrokeColor(c color.Color) {
+	dc.color = c
+	dc.fillPattern = NewSolidPattern(c)
+	dc.strokePattern = NewSolidPattern(c)
+}
+
+// SetFillStyle sets current fill style
+func (dc *Context) SetFillStyle(pattern Pattern) {
+	// if pattern is SolidPattern, also change dc.color(for dc.Clear, dc.drawString)
+	if fillStyle, ok := pattern.(*solidPattern); ok {
+		dc.color = fillStyle.color
+	}
+	dc.fillPattern = pattern
+}
+
+// SetStrokeStyle sets current stroke style
+func (dc *Context) SetStrokeStyle(pattern Pattern) {
+	dc.strokePattern = pattern
+}
+
+// SetColor sets the current color(for both fill and stroke).
+func (dc *Context) SetColor(c color.Color) {
+	dc.setFillAndStrokeColor(c)
+}
+
+// SetHexColor sets the current color using a hex string. The leading pound
+// sign (#) is optional. Both 3- and 6-digit variations are supported. 8 digits
+// may be provided to set the alpha value as well.
+func (dc *Context) SetHexColor(x string) {
+	r, g, b, a := parseHexColor(x)
+	dc.SetRGBA255(r, g, b, a)
+}
+
+// SetRGBA255 sets the current color. r, g, b, a values should be between 0 and
+// 255, inclusive.
+func (dc *Context) SetRGBA255(r, g, b, a int) {
+	dc.color = color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
+	dc.setFillAndStrokeColor(dc.color)
+}
+
+// SetRGB255 sets the current color. r, g, b values should be between 0 and 255,
+// inclusive. Alpha will be set to 255 (fully opaque).
+func (dc *Context) SetRGB255(r, g, b int) {
+	dc.SetRGBA255(r, g, b, 255)
+}
+
+// SetRGBA sets the current color. r, g, b, a values should be between 0 and 1,
+// inclusive.
+func (dc *Context) SetRGBA(r, g, b, a float64) {
+	dc.color = color.NRGBA{
+		uint8(r * 255),
+		uint8(g * 255),
+		uint8(b * 255),
+		uint8(a * 255),
+	}
+	dc.setFillAndStrokeColor(dc.color)
+}
+
+// SetRGB sets the current color. r, g, b values should be between 0 and 1,
+// inclusive. Alpha will be set to 1 (fully opaque).
+func (dc *Context) SetRGB(r, g, b float64) {
+	dc.SetRGBA(r, g, b, 1)
+}
+
+// Path Manipulation
+
+// MoveTo starts a new subpath within the current path starting at the
+// specified point.
+func (dc *Context) MoveTo(x, y float64) {
+	if dc.hasCurrent {
+		dc.fillPath.Add1(dc.start.Fixed())
+	}
+	x, y = dc.TransformPoint(x, y)
+	p := Point{x, y}
+	dc.strokePath.Start(p.Fixed())
+	dc.fillPath.Start(p.Fixed())
+	dc.start = p
+	dc.current = p
+	dc.hasCurrent = true
+}
+
+// LineTo adds a line segment to the current path starting at the current
+// point. If there is no current point, it is equivalent to MoveTo(x, y)
+func (dc *Context) LineTo(x, y float64) {
+	if !dc.hasCurrent {
+		dc.MoveTo(x, y)
+	} else {
+		x, y = dc.TransformPoint(x, y)
+		p := Point{x, y}
+		dc.strokePath.Add1(p.Fixed())
+		dc.fillPath.Add1(p.Fixed())
+		dc.current = p
+	}
+}
+
+// QuadraticTo adds a quadratic bezier curve to the current path starting at
+// the current point. If there is no current point, it first performs
+// MoveTo(x1, y1)
+func (dc *Context) QuadraticTo(x1, y1, x2, y2 float64) {
+	if !dc.hasCurrent {
+		dc.MoveTo(x1, y1)
+	}
+	x1, y1 = dc.TransformPoint(x1, y1)
+	x2, y2 = dc.TransformPoint(x2, y2)
+	p1 := Point{x1, y1}
+	p2 := Point{x2, y2}
+	dc.strokePath.Add2(p1.Fixed(), p2.Fixed())
+	dc.fillPath.Add2(p1.Fixed(), p2.Fixed())
+	dc.current = p2
+}
+
+// CubicTo adds a cubic bezier curve to the current path starting at the
+// current point. If there is no current point, it first performs
+// MoveTo(x1, y1). Because freetype/raster does not support cubic beziers,
+// this is emulated with many small line segments.
+func (dc *Context) CubicTo(x1, y1, x2, y2, x3, y3 float64) {
+	if !dc.hasCurrent {
+		dc.MoveTo(x1, y1)
+	}
+	x0, y0 := dc.current.X, dc.current.Y
+	x1, y1 = dc.TransformPoint(x1, y1)
+	x2, y2 = dc.TransformPoint(x2, y2)
+	x3, y3 = dc.TransformPoint(x3, y3)
+	points := CubicBezier(x0, y0, x1, y1, x2, y2, x3, y3)
+	previous := dc.current.Fixed()
+	for _, p := range points[1:] {
+		f := p.Fixed()
+		if f == previous {
+			// TODO: this fixes some rendering issues but not all
+			continue
+		}
+		previous = f
+		dc.strokePath.Add1(f)
+		dc.fillPath.Add1(f)
+		dc.current = p
+	}
+}
+
+// ClosePath adds a line segment from the current point to the beginning
+// of the current subpath. If there is no current point, this is a no-op.
+func (dc *Context) ClosePath() {
+	if dc.hasCurrent {
+		dc.strokePath.Add1(dc.start.Fixed())
+		dc.fillPath.Add1(dc.start.Fixed())
+		dc.current = dc.start
+	}
+}
+
+// ClearPath clears the current path. There is no current point after this
+// operation.
+func (dc *Context) ClearPath() {
+	dc.strokePath.Clear()
+	dc.fillPath.Clear()
+	dc.hasCurrent = false
+}
+
+// NewSubPath starts a new subpath within the current path. There is no current
+// point after this operation.
+func (dc *Context) NewSubPath() {
+	if dc.hasCurrent {
+		dc.fillPath.Add1(dc.start.Fixed())
+	}
+	dc.hasCurrent = false
+}
+
+// Path Drawing
+
+func (dc *Context) capper() raster.Capper {
+	switch dc.lineCap {
+	case LineCapButt:
+		return raster.ButtCapper
+	case LineCapRound:
+		return raster.RoundCapper
+	case LineCapSquare:
+		return raster.SquareCapper
+	}
+	return nil
+}
+
+func (dc *Context) joiner() raster.Joiner {
+	switch dc.lineJoin {
+	case LineJoinBevel:
+		return raster.BevelJoiner
+	case LineJoinRound:
+		return raster.RoundJoiner
+	}
+	return nil
+}
+
+func (dc *Context) stroke(painter raster.Painter) {
+	path := dc.strokePath
+	if len(dc.dashes) > 0 {
+		path = dashed(path, dc.dashes)
+	} else {
+		// TODO: this is a temporary workaround to remove tiny segments
+		// that result in rendering issues
+		path = rasterPath(flattenPath(path))
+	}
+	r := raster.NewRasterizer(dc.width, dc.height)
+	r.UseNonZeroWinding = true
+	r.AddStroke(path, fix(dc.lineWidth), dc.capper(), dc.joiner())
+	r.Rasterize(painter)
+}
+
+func (dc *Context) fill(painter raster.Painter) {
+	path := dc.fillPath
+	if dc.hasCurrent {
+		path = make(raster.Path, len(dc.fillPath))
+		copy(path, dc.fillPath)
+		path.Add1(dc.start.Fixed())
+	}
+	r := raster.NewRasterizer(dc.width, dc.height)
+	r.UseNonZeroWinding = dc.fillRule == FillRuleWinding
+	r.AddPath(path)
+	r.Rasterize(painter)
+}
+
+// StrokePreserve strokes the current path with the current color, line width,
+// line cap, line join and dash settings. The path is preserved after this
+// operation.
+func (dc *Context) StrokePreserve() {
+	painter := newPatternPainter(dc.im, dc.mask, dc.strokePattern)
+	dc.stroke(painter)
+}
+
+// Stroke strokes the current path with the current color, line width,
+// line cap, line join and dash settings. The path is cleared after this
+// operation.
+func (dc *Context) Stroke() {
+	dc.StrokePreserve()
+	dc.ClearPath()
+}
+
+// FillPreserve fills the current path with the current color. Open subpaths
+// are implicity closed. The path is preserved after this operation.
+func (dc *Context) FillPreserve() {
+	painter := newPatternPainter(dc.im, dc.mask, dc.fillPattern)
+	dc.fill(painter)
+}
+
+// Fill fills the current path with the current color. Open subpaths
+// are implicity closed. The path is cleared after this operation.
+func (dc *Context) Fill() {
+	dc.FillPreserve()
+	dc.ClearPath()
+}
+
+// ClipPreserve updates the clipping region by intersecting the current
+// clipping region with the current path as it would be filled by dc.Fill().
+// The path is preserved after this operation.
+func (dc *Context) ClipPreserve() {
+	clip := image.NewAlpha(image.Rect(0, 0, dc.width, dc.height))
+	painter := raster.NewAlphaOverPainter(clip)
+	dc.fill(painter)
+	if dc.mask == nil {
+		dc.mask = clip
+	} else {
+		mask := image.NewAlpha(image.Rect(0, 0, dc.width, dc.height))
+		draw.DrawMask(mask, mask.Bounds(), clip, image.ZP, dc.mask, image.ZP, draw.Over)
+		dc.mask = mask
+	}
+}
+
+// SetMask allows you to directly set the *image.Alpha to be used as a clipping
+// mask. It must be the same size as the context, else an error is returned
+// and the mask is unchanged.
+func (dc *Context) SetMask(mask *image.Alpha) error {
+	if mask.Bounds().Size() != dc.im.Bounds().Size() {
+		return errors.New("mask size must match context size")
+	}
+	dc.mask = mask
+	return nil
+}
+
+// AsMask returns an *image.Alpha representing the alpha channel of this
+// context. This can be useful for advanced clipping operations where you first
+// render the mask geometry and then use it as a mask.
+func (dc *Context) AsMask() *image.Alpha {
+	mask := image.NewAlpha(dc.im.Bounds())
+	draw.Draw(mask, dc.im.Bounds(), dc.im, image.ZP, draw.Src)
+	return mask
+}
+
+// Clip updates the clipping region by intersecting the current
+// clipping region with the current path as it would be filled by dc.Fill().
+// The path is cleared after this operation.
+func (dc *Context) Clip() {
+	dc.ClipPreserve()
+	dc.ClearPath()
+}
+
+// ResetClip clears the clipping region.
+func (dc *Context) ResetClip() {
+	dc.mask = nil
+}
+
+// Convenient Drawing Functions
+
+// Clear fills the entire image with the current color.
+func (dc *Context) Clear() {
+	src := image.NewUniform(dc.color)
+	draw.Draw(dc.im, dc.im.Bounds(), src, image.ZP, draw.Src)
+}
+
+// SetPixel sets the color of the specified pixel using the current color.
+func (dc *Context) SetPixel(x, y int) {
+	dc.im.Set(x, y, dc.color)
+}
+
+// DrawPoint is like DrawCircle but ensures that a circle of the specified
+// size is drawn regardless of the current transformation matrix. The position
+// is still transformed, but not the shape of the point.
+func (dc *Context) DrawPoint(x, y, r float64) {
+	dc.Push()
+	tx, ty := dc.TransformPoint(x, y)
+	dc.Identity()
+	dc.DrawCircle(tx, ty, r)
+	dc.Pop()
+}
+
+func (dc *Context) DrawLine(x1, y1, x2, y2 float64) {
+	dc.MoveTo(x1, y1)
+	dc.LineTo(x2, y2)
+}
+
+func (dc *Context) DrawRectangle(x, y, w, h float64) {
+	dc.NewSubPath()
+	dc.MoveTo(x, y)
+	dc.LineTo(x+w, y)
+	dc.LineTo(x+w, y+h)
+	dc.LineTo(x, y+h)
+	dc.ClosePath()
+}
+
+func (dc *Context) DrawRoundedRectangle(x, y, w, h, r float64) {
+	x0, x1, x2, x3 := x, x+r, x+w-r, x+w
+	y0, y1, y2, y3 := y, y+r, y+h-r, y+h
+	dc.NewSubPath()
+	dc.MoveTo(x1, y0)
+	dc.LineTo(x2, y0)
+	dc.DrawArc(x2, y1, r, Radians(270), Radians(360))
+	dc.LineTo(x3, y2)
+	dc.DrawArc(x2, y2, r, Radians(0), Radians(90))
+	dc.LineTo(x1, y3)
+	dc.DrawArc(x1, y2, r, Radians(90), Radians(180))
+	dc.LineTo(x0, y1)
+	dc.DrawArc(x1, y1, r, Radians(180), Radians(270))
+	dc.ClosePath()
+}
+
+func (dc *Context) DrawEllipticalArc(x, y, rx, ry, angle1, angle2 float64) {
+	const n = 16
+	for i := 0; i < n; i++ {
+		p1 := float64(i+0) / n
+		p2 := float64(i+1) / n
+		a1 := angle1 + (angle2-angle1)*p1
+		a2 := angle1 + (angle2-angle1)*p2
+		x0 := x + rx*math.Cos(a1)
+		y0 := y + ry*math.Sin(a1)
+		x1 := x + rx*math.Cos(a1+(a2-a1)/2)
+		y1 := y + ry*math.Sin(a1+(a2-a1)/2)
+		x2 := x + rx*math.Cos(a2)
+		y2 := y + ry*math.Sin(a2)
+		cx := 2*x1 - x0/2 - x2/2
+		cy := 2*y1 - y0/2 - y2/2
+		if i == 0 {
+			if dc.hasCurrent {
+				dc.LineTo(x0, y0)
+			} else {
+				dc.MoveTo(x0, y0)
+			}
+		}
+		dc.QuadraticTo(cx, cy, x2, y2)
+	}
+}
+
+func (dc *Context) DrawEllipse(x, y, rx, ry float64) {
+	dc.NewSubPath()
+	dc.DrawEllipticalArc(x, y, rx, ry, 0, 2*math.Pi)
+	dc.ClosePath()
+}
+
+func (dc *Context) DrawArc(x, y, r, angle1, angle2 float64) {
+	dc.DrawEllipticalArc(x, y, r, r, angle1, angle2)
+}
+
+func (dc *Context) DrawCircle(x, y, r float64) {
+	dc.NewSubPath()
+	dc.DrawEllipticalArc(x, y, r, r, 0, 2*math.Pi)
+	dc.ClosePath()
+}
+
+func (dc *Context) DrawRegularPolygon(n int, x, y, r, rotation float64) {
+	angle := 2 * math.Pi / float64(n)
+	rotation -= math.Pi / 2
+	if n%2 == 0 {
+		rotation += angle / 2
+	}
+	dc.NewSubPath()
+	for i := 0; i < n; i++ {
+		a := rotation + angle*float64(i)
+		dc.LineTo(x+r*math.Cos(a), y+r*math.Sin(a))
+	}
+	dc.ClosePath()
+}
+
+// DrawImage draws the specified image at the specified point.
+func (dc *Context) DrawImage(im image.Image, x, y int) {
+	dc.DrawImageAnchored(im, x, y, 0, 0)
+}
+
+// DrawImageAnchored draws the specified image at the