x/canvas/canvas.go

package xcanvas

import "image"
import "image/color"
import "github.com/jezek/xgbutil"
import "github.com/jezek/xgb/xproto"
import "git.tebibyte.media/tomo/ggfx"
import "github.com/jezek/xgbutil/xgraphics"
import "git.tebibyte.media/tomo/tomo/canvas"

// Canvas satisfies the canvas.Canvas interface. It draws to an xgraphics.Image.
type Canvas struct {
	*xgraphics.Image
}

// New creates a new canvas from a bounding rectangle.
func New (x *xgbutil.XUtil, bounds image.Rectangle) *Canvas {
	return NewFrom(xgraphics.New(x, bounds))
}

// NewFrom creates a new canvas from an existing xgraphics.Image.
func NewFrom (image *xgraphics.Image) *Canvas {
	if image == nil { return nil }
	return &Canvas { image }
}

// Pen returns a new drawing context.
func (this *Canvas) Pen () canvas.Pen {
	return &pen {
		image: this.Image,
		gfx:   ggfx.Image[uint8] {
			Pix:    this.Image.Pix,
			Stride: this.Image.Stride,
			Rect:   this.Image.Rect,
			Width:  4,
		},
	}
}

// Clip returns a sub-canvas of this canvas.
func (this *Canvas) Clip (bounds image.Rectangle) canvas.Canvas {
	this.assert()
	subImage := this.Image.SubImage(bounds)
	if subImage == nil { return nil }
	xImage := subImage.(*xgraphics.Image)
	return &Canvas { xImage }
}

// Push pushes this canvas to the screen.
func (this *Canvas) Push (window xproto.Window) {
	this.assert()
	this.XDraw()
	this.XExpPaint(window, this.Bounds().Min.X, this.Bounds().Min.Y)
}

func (this *Canvas) assert () {
	if this == nil { panic("nil canvas") }
}

// TODO: we need to implement:
//  - cap
//  - joint
//  - align

type pen struct {
	image *xgraphics.Image
	gfx    ggfx.Image[uint8]

	closed bool
	endCap canvas.Cap
	joint  canvas.Joint
	weight int
	align  canvas.StrokeAlign
	stroke [4]uint8
	fill   [4]uint8
}

func (this *pen) Rectangle (bounds image.Rectangle) {
	if this.weight == 0 {
		this.gfx.FillRectangle(this.fill[:], bounds)
	} else {
		this.gfx.StrokeRectangle(this.stroke[:], this.weight, bounds)
	}
}

func (this *pen) Path (points ...image.Point) {
	if this.weight == 0 {
		this.gfx.FillPolygon(this.fill[:], points...)
	} else if this.closed {
		this.gfx.StrokePolygon(this.stroke[:], this.weight, points...)
	} else {
		this.gfx.PolyLine(this.stroke[:], this.weight, points...)
	}
}
 
func (this *pen) Closed       (closed bool)              { this.closed = closed }
func (this *pen) Cap          (endCap canvas.Cap)        { this.endCap = endCap }
func (this *pen) Joint        (joint  canvas.Joint)      { this.joint  = joint  }
func (this *pen) StrokeWeight (weight int)               { this.weight = weight }
func (this *pen) StrokeAlign  (align canvas.StrokeAlign) { this.align  = align  }

func (this *pen) Stroke (stroke color.Color) { this.stroke = convertColor(stroke) }
func (this *pen) Fill (fill color.Color)     { this.fill   = convertColor(fill)   }

func convertColor (c color.Color) [4]uint8 {
	r, g, b, a := c.RGBA()
	return [4]uint8 {
		uint8(b >> 8),
		uint8(g >> 8),
		uint8(r >> 8),
		uint8(a >> 8),
	}
}