Add vector package (Work in progress)

examples/vector/main.go

@@ -0,0 +1,53 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build example jsgo
+
+package main
+
+import (
+	"image/color"
+	"log"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/vector"
+)
+
+const (
+	screenWidth  = 640
+	screenHeight = 480
+)
+
+func update(screen *ebiten.Image) error {
+	if ebiten.IsDrawingSkipped() {
+		return nil
+	}
+
+	var path vector.Path
+	path.MoveTo(20, 20)
+	path.LineTo(30, 50)
+
+	op := &vector.DrawPathOptions{}
+	op.LineWidth = 4
+	op.StrokeColor = color.White
+	path.Draw(screen, op)
+
+	return nil
+}
+
+func main() {
+	if err := ebiten.Run(update, screenWidth, screenHeight, 1, "Vector (Ebiten Demo)"); err != nil {
+		log.Fatal(err)
+	}
+}

vector/path.go

@@ -0,0 +1,154 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package vector provides functions for vector graphics rendering.
+//
+// This package is under experiments and the API might be changed with breaking backward compatibility.
+package vector
+
+import (
+	"image/color"
+	"math"
+
+	"github.com/hajimehoshi/ebiten"
+)
+
+var emptyImage *ebiten.Image
+
+func init() {
+	const w, h = 16, 16
+	emptyImage, _ = ebiten.NewImage(w, h, ebiten.FilterDefault)
+	pix := make([]byte, 4*w*h)
+	for i := range pix {
+		pix[i] = 0xff
+	}
+	emptyImage.ReplacePixels(pix)
+}
+
+type point struct {
+	x float32
+	y float32
+}
+
+type segment struct {
+	p0 point
+	p1 point
+}
+
+func (s *segment) atan2() float64 {
+	return math.Atan2(float64(s.p1.y-s.p0.y), float64(s.p1.x-s.p0.x))
+}
+
+// Path represents a collection of paths.
+type Path struct {
+	segs []segment
+	cur  point
+}
+
+// MoveTo skips the current position of the path to the given position (x, y) without adding any strokes.
+func (p *Path) MoveTo(x, y float32) {
+	p.cur = point{x, y}
+}
+
+// LineTo adds a segment to the path, which starts from the current position and ends to the given position (x, y).
+//
+// LineTo updates the current position to (x, y).
+func (p *Path) LineTo(x, y float32) {
+	p.segs = append(p.segs, segment{p.cur, point{x, y}})
+	p.cur = point{x, y}
+}
+
+func (p *Path) strokeVertices(lineWidth float32, clr color.Color) (vertices []ebiten.Vertex, indices []uint16) {
+	if len(p.segs) == 0 {
+		return nil, nil
+	}
+
+	sw, sh := emptyImage.Size()
+	r, g, b, a := clr.RGBA()
+	rf, gf, bf, af := float32(r/0xffff), float32(g/0xffff), float32(b/0xffff), float32(a/0xffff)
+	for i, s := range p.segs {
+		si, co := math.Sincos(s.atan2() + math.Pi/2)
+		dx, dy := float32(co)*lineWidth/2, float32(si)*lineWidth/2
+		v0 := point{s.p0.x + dx, s.p0.y + dy}
+		v1 := point{s.p0.x - dx, s.p0.y - dy}
+		v2 := point{s.p1.x + dx, s.p1.y + dy}
+		v3 := point{s.p1.x - dx, s.p1.y - dy}
+
+		vertices = append(vertices,
+			ebiten.Vertex{
+				DstX:   v0.x,
+				DstY:   v0.y,
+				SrcX:   0,
+				SrcY:   0,
+				ColorR: rf,
+				ColorG: gf,
+				ColorB: bf,
+				ColorA: af,
+			},
+			ebiten.Vertex{
+				DstX:   v1.x,
+				DstY:   v1.y,
+				SrcX:   float32(sw),
+				SrcY:   0,
+				ColorR: rf,
+				ColorG: gf,
+				ColorB: bf,
+				ColorA: af,
+			},
+			ebiten.Vertex{
+				DstX:   v2.x,
+				DstY:   v2.y,
+				SrcX:   0,
+				SrcY:   float32(sh),
+				ColorR: rf,
+				ColorG: gf,
+				ColorB: bf,
+				ColorA: af,
+			},
+			ebiten.Vertex{
+				DstX:   v3.x,
+				DstY:   v3.y,
+				SrcX:   float32(sw),
+				SrcY:   float32(sh),
+				ColorR: rf,
+				ColorG: gf,
+				ColorB: bf,
+				ColorA: af,
+			},
+		)
+		idx := uint16(4 * i)
+		indices = append(indices, idx, idx+1, idx+2, idx+1, idx+2, idx+3)
+	}
+
+	return
+}
+
+// DrawPathOptions is the options specified at (*Path).Draw.
+type DrawPathOptions struct {
+	LineWidth   float32
+	StrokeColor color.Color
+}
+
+// Draw draws the path by rendering its stroke or filling.
+func (p *Path) Draw(target *ebiten.Image, op *DrawPathOptions) {
+	if op == nil {
+		return
+	}
+
+	// TODO: Implement filling
+	if op.StrokeColor != nil {
+		vs, is := p.strokeVertices(op.LineWidth, op.StrokeColor)
+		target.DrawTriangles(vs, is, emptyImage, nil)
+	}
+}