p5: add Key callback

event.go

@@ -4,6 +4,8 @@
 
 package p5
 
+import "gioui.org/io/key"
+
 // Event is the current event pushed from the system.
 var Event struct {
 	Mouse struct {
@@ -18,6 +20,11 @@ var Event struct {
 		}
 		Buttons Buttons
 	}
+
+	Key struct {
+		Cur  key.Event
+		Prev key.Event
+	}
 }
 
 // Buttons is a set of mouse buttons.

example/key-pressed/main.go

@@ -0,0 +1,48 @@
+// Copyright ©2021 The go-p5 Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"image/color"
+
+	"gioui.org/io/key"
+	"github.com/go-p5/p5"
+)
+
+func main() {
+	p5.Run(setup, draw, p5.WithKeyCallback(kcbk))
+}
+
+func setup() {
+	p5.Canvas(400, 400)
+	p5.Background(color.Gray{Y: 220})
+}
+
+func draw() {
+	switch p5.Event.Key.Cur.State {
+	case key.Press:
+		p5.Stroke(color.Black)
+		p5.Fill(color.RGBA{R: 255, A: 255})
+	default:
+		p5.Stroke(nil)
+		p5.Fill(color.Transparent)
+	}
+	p5.Ellipse(
+		200, 200,
+		100, 100,
+	)
+
+	p5.TextSize(24)
+	p5.Text(fmt.Sprintf("count=%d", cnt), 10, 390)
+}
+
+var cnt int
+
+func kcbk() {
+	if p5.Event.Key.Cur.State == key.Press && p5.Event.Key.Prev.State != key.Press {
+		cnt++
+	}
+}

example/key-snake/main.go

@@ -0,0 +1,78 @@
+// Copyright ©2021 The go-p5 Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"image/color"
+
+	"gioui.org/io/key"
+	"github.com/go-p5/p5"
+)
+
+func main() {
+	p5.Run(setup, draw, p5.WithKeyCallback(kcbk))
+}
+
+const (
+	width  = 400
+	height = 400
+)
+
+func setup() {
+	p5.Canvas(width, height)
+	p5.Stroke(nil)
+	p5.Background(color.Gray{Y: 220})
+}
+
+var (
+	xs = make([]float64, 50)
+	ys = make([]float64, 50)
+
+	px, py float64
+)
+
+func draw() {
+	for i := 1; i < len(xs); i++ {
+		xs[i-1] = xs[i]
+		ys[i-1] = ys[i]
+	}
+
+	xs[len(xs)-1] = px
+	ys[len(xs)-1] = py
+
+	for i := range xs {
+		p5.Fill(color.RGBA{R: 255, A: uint8(i * 5)})
+		p5.Ellipse(xs[i], ys[i], float64(i), float64(i))
+	}
+}
+
+func kcbk() {
+	cur := p5.Event.Key.Cur
+	if cur.State != key.Press {
+		return
+	}
+	switch cur.Name {
+	case key.NameLeftArrow:
+		px -= 5
+	case key.NameRightArrow:
+		px += 5
+	case key.NameUpArrow:
+		py -= 5
+	case key.NameDownArrow:
+		py += 5
+	}
+	px = clip(px, 0, width)
+	py = clip(py, 0, height)
+}
+
+func clip(x, min, max float64) float64 {
+	switch {
+	case x < min:
+		x = min
+	case x > max:
+		x = max
+	}
+	return x
+}

p5.go

@@ -40,11 +40,35 @@ var (
 
 // Run executes the user functions setup and draw.
 // Run never exits.
-func Run(setup, draw Func) {
+func Run(setup, draw Func, opts ...Option) {
 	gproc.Setup = setup
 	gproc.Draw = draw
+
+	for _, opt := range opts {
+		opt(gproc)
+	}
+
 	gproc.Run()
 }
 
 // Func is the type of functions users provide to p5.
 type Func func()
+
+// Option customizes further a p5 processor.
+type Option func(p *Proc)
+
+// WithKeyCallback binds the given function to the p5 processor's
+// key callback.
+func WithKeyCallback(f Func) Option {
+	return func(p *Proc) {
+		p.Key = f
+	}
+}
+
+// WithMouseCallback binds the given function to the p5 processor's
+// mouse callback.
+func WithMouseCallback(f Func) Option {
+	return func(p *Proc) {
+		p.Mouse = f
+	}
+}

proc.go

@@ -82,6 +82,7 @@ type Proc struct {
 	Setup Func
 	Draw  Func
 	Mouse Func
+	Key   Func
 
 	ctl struct {
 		FrameRate time.Duration
@@ -238,6 +239,10 @@ func (p *Proc) run() error {
 			return e.Err
 
 		case key.Event:
+			Event.Key.Prev = Event.Key.Cur
+			Event.Key.Cur = e
+			p.Key()
+
 			switch e.Name {
 			case key.NameEscape:
 				w.Close()
@@ -282,6 +287,9 @@ func (p *Proc) setupUserFuncs() {
 	if p.Mouse == nil {
 		p.Mouse = func() {}
 	}
+	if p.Key == nil {
+		p.Key = func() {}
+	}
 }
 
 func (p *Proc) draw(e system.FrameEvent) {