canvas.go

package giopdf

import (
	"image"
	"image/color"

	"gioui.org/f32"
	"gioui.org/op"
	"gioui.org/op/clip"
	"gioui.org/op/paint"
	"github.com/andybalholm/stroke"
)

// A Canvas implements the PDF imaging model, drawing to a Gio operations list.
// Most of its methods correspond directly to PDF page description operators.
type Canvas struct {
	PathBuilder
	graphicsState

	stateStack      []graphicsState
	setClippingPath bool

	ops *op.Ops
}

func NewCanvas(ops *op.Ops) *Canvas {
	return &Canvas{
		ops: ops,
		graphicsState: graphicsState{
			fillColor:   color.NRGBA{0, 0, 0, 255},
			strokeColor: color.NRGBA{0, 0, 0, 255},
			lineWidth:   1,
			miterLimit:  10,
			hScale:      100,
		},
	}
}

func (c *Canvas) fill() {
	ps := toPathSpec(c.ops, c.Path, true)
	paint.FillShape(c.ops, c.fillColor, clip.Outline{ps}.Op())
}

func (c *Canvas) stroke() {
	var p [][]stroke.Segment
	var contour []stroke.Segment
	var pos, lastMove f32.Point
	for _, e := range c.Path {
		switch e.Op {
		case 'm':
			lastMove = e.End
			pos = e.End
			if len(contour) > 0 {
				p = append(p, contour)
				contour = nil
			}
		case 'l':
			contour = append(contour, stroke.LinearSegment(stroke.Point(pos), stroke.Point(e.End)))
			pos = e.End
		case 'c':
			contour = append(contour, stroke.Segment{stroke.Point(pos), stroke.Point(e.CP1), stroke.Point(e.CP2), stroke.Point(e.End)})
			pos = e.End
		case 'h':
			if pos != lastMove {
				contour = append(contour, stroke.LinearSegment(stroke.Point(pos), stroke.Point(lastMove)))
				pos = lastMove
			}
		}
	}
	if len(contour) > 0 {
		p = append(p, contour)
		contour = nil
	}

	if len(c.dashes) > 0 {
		p = stroke.Dash(p, c.dashes, c.dashPhase)
	}

	outline := stroke.Stroke(p, stroke.Options{
		Width:      c.lineWidth,
		Cap:        stroke.CapStyle(c.lineCap),
		Join:       stroke.JoinStyle(c.lineJoin),
		MiterLimit: c.miterLimit,
	})

	ps := segmentsToPathSpec(c.ops, outline)
	paint.FillShape(c.ops, c.strokeColor, clip.Outline{ps}.Op())
}

func segmentsToPathSpec(ops *op.Ops, outline [][]stroke.Segment) clip.PathSpec {
	var path clip.Path
	path.Begin(ops)

	for _, contour := range outline {
		path.MoveTo(f32.Point(contour[0].Start))
		for i, s := range contour {
			if i > 0 && s.Start != contour[i-1].End {
				path.LineTo(f32.Point(s.Start))
			}
			path.CubeTo(f32.Point(s.CP1), f32.Point(s.CP2), f32.Point(s.End))
		}
	}
	return path.End()
}

func (c *Canvas) finishPath() {
	if c.setClippingPath {
		ps := toPathSpec(c.ops, c.Path, true)
		cs := clip.Outline{ps}.Op().Push(c.ops)
		c.clippingPaths = append(c.clippingPaths, cs)
	}
	c.setClippingPath = false
	c.Path = c.Path[:0]
}

// Fill fills the current path.
func (c *Canvas) Fill() {
	c.fill()
	c.finishPath()
}

// Stroke strokes (outlines) the current path.
func (c *Canvas) Stroke() {
	c.stroke()
	c.finishPath()
}

// CloseAndStroke closes the current path before stroking it it.
func (c *Canvas) CloseAndStroke() {
	c.ClosePath()
	c.stroke()
	c.finishPath()
}

// FillAndStroke fills the current path and then strokes (outlines) it.
func (c *Canvas) FillAndStroke() {
	c.fill()
	c.stroke()
	c.finishPath()
}

// NoOpPaint finishes the current path without filling or stroking it.
// It is normally used to apply a clipping path after calling Clip.
func (c *Canvas) NoOpPaint() {
	c.finishPath()
}

// Clip causes the current path to be added to the clipping path after it is
// painted.
func (c *Canvas) Clip() {
	c.setClippingPath = true
}

// CloseFillAndStroke closes the current path before filling and stroking it.
func (c *Canvas) CloseFillAndStroke() {
	c.ClosePath()
	c.fill()
	c.stroke()
	c.finishPath()
}

// Save pushes a copy of the current graphics state onto the state stack.
func (c *Canvas) Save() {
	c.stateStack = append(c.stateStack, c.graphicsState)
	c.transforms = nil
	c.clippingPaths = nil
}

// Restore restores the graphics state, popping it off the stack.
func (c *Canvas) Restore() {
	// First pop off the TransformStack and clip.Stack entries that were saved since the last Save call.
	for i := len(c.transforms) - 1; i >= 0; i-- {
		c.transforms[i].Pop()
	}
	for i := len(c.clippingPaths) - 1; i >= 0; i-- {
		c.clippingPaths[i].Pop()
	}

	n := len(c.stateStack) - 1
	c.graphicsState = c.stateStack[n]
	c.stateStack = c.stateStack[:n]
}

// Transform changes the coordinate system according to the transformation
// matrix specified.
func (ca *Canvas) Transform(a, b, c, d, e, f float32) {
	m := f32.NewAffine2D(a, c, e, b, d, f)
	s := op.Affine(m).Push(ca.ops)
	ca.transforms = append(ca.transforms, s)
}

// Image draws an image. The image is placed in the unit square of the user
// coordinate system.
func (c *Canvas) Image(img image.Image) {
	io := paint.NewImageOp(img)
	size := io.Size()
	c.Save()
	c.Transform(1/float32(size.X), 0, 0, -1/float32(size.Y), 0, 1)
	io.Add(c.ops)
	paint.PaintOp{}.Add(c.ops)
	c.Restore()
}