giocanvas client example with new Gio filter event API:

filter-api.go

// kbpointer processes the keyboard events and pointer events in percent coordinates
func kbpointer(q input.Source, cfg config) {
	width, height := cfg.width, cfg.height
	prec := cfg.precision
	stepsize := cfg.stepsize
	for {
		e, ok := q.Event(
			key.Filter{Optional: key.ModCtrl},
			pointer.Filter{Kinds: pointer.Press | pointer.Move | pointer.Release},
		)
		if !ok {
			break
		}
		switch e := e.(type) {

		case key.Event: // keyboard events

			switch e.State {
			case key.Press:
				switch e.Name {
				case "G":
					dogrid = !dogrid
				case "A":
					shape = "arc"
				case "L":
					shape = "line"
				case "B":
					shape = "bezier"
				case "C":
					shape = "circle"
				case "S":
					shape = "square"
				case "R":
					shape = "rect"
				case "E":
					shape = "ellipse"
				case "D":
					deckspec(prec)
				case key.NameRightArrow:
					switch e.Modifiers {
					case 0:
						bx += stepsize
					case key.ModCtrl:
						ex += stepsize
					}
				case key.NameLeftArrow:
					switch e.Modifiers {
					case 0:
						bx -= stepsize
					case key.ModCtrl:
						ex -= stepsize
					}
				case key.NameUpArrow:
					switch e.Modifiers {
					case 0:
						by += stepsize
					case key.ModCtrl:
						ey += stepsize
					}
				case key.NameDownArrow:
					switch e.Modifiers {
					case 0:
						by -= stepsize
					case key.ModCtrl:
						ey -= stepsize
					}
				case key.NameEscape, "Q":
					os.Exit(0)
				}
			}

		case pointer.Event: // pointer events

			switch e.Kind {
			case pointer.Move:
				mouseX, mouseY = pctcoord(e.Position.X, e.Position.Y, width, height)
			case pointer.Press:
				switch e.Buttons {
				case pointer.ButtonPrimary:
					bx, by = pctcoord(e.Position.X, e.Position.Y, width, height)
				case pointer.ButtonSecondary:
					ex, ey = pctcoord(e.Position.X, e.Position.Y, width, height)
				case pointer.ButtonTertiary:
					deckspec(prec)
				}
			}
		}
	}
}

func shapesketch(w *app.Window, cfg config) error {
	// initial values
	bx, by = 25.0, 50.0
	ex, ey = 75.0, 50.0
	cx, cy = 10, 10
	shape = "bezier"
	begincolor, endcolor, shapecolor := cfg.begincolor, cfg.endcolor, cfg.shapecolor

	// app loop
	for {
		ev := w.NextEvent()
		switch e := ev.(type) {
		// return an error on close
		case app.DestroyEvent:
			return e.Err
		// for each frame: register keyboard, pointer press and move events, draw coordinates and
		// specified shapes. Track the pointer position for the current point.
		case app.FrameEvent:
			canvas := giocanvas.NewCanvas(float32(e.Size.X), float32(e.Size.Y), app.FrameEvent{})
			canvas.Background(cfg.bgcolor)
			grid(canvas, 5, cfg.textcolor)
			// draw specified shape
			switch shape {
			case "line":
				textcoord(canvas, bx, by, begincolor, cfg)
				textcoord(canvas, ex, ey, endcolor, cfg)
				canvas.Line(bx, by, ex, ey, cfg.linesize, cfg.shapecolor)
			case "bezier":
				textcoord(canvas, bx, by, begincolor, cfg)
				textcoord(canvas, ex, ey, endcolor, cfg)
				textcoord(canvas, cx, cy, shapecolor, cfg)
				canvas.QuadStrokedCurve(bx, by, cx, cy, ex, ey, cfg.linesize, cfg.shapecolor)
			case "circle":
				textcoord(canvas, bx, by, begincolor, cfg)
				textcoord(canvas, cx, cy, shapecolor, cfg)
				canvas.Circle(bx, by, dist(bx, by, cx, cy), cfg.shapecolor)
			case "square":
				textcoord(canvas, bx, by, begincolor, cfg)
				textcoord(canvas, cx, cy, shapecolor, cfg)
				canvas.Square(bx, by, (cx-bx)*2, cfg.shapecolor)
			case "ellipse":
				textcoord(canvas, bx, by, begincolor, cfg)
				textcoord(canvas, cx, cy, shapecolor, cfg)
				canvas.Ellipse(bx, by, (cx-bx)*2, (cy-by)*2, cfg.shapecolor)
			case "rect":
				textcoord(canvas, bx, by, begincolor, cfg)
				textcoord(canvas, cx, cy, shapecolor, cfg)
				canvas.CenterRect(bx, by, (cx-bx)*2, (cy-by)*2, cfg.shapecolor)
			case "arc":
				textcoord(canvas, bx, by, begincolor, cfg)
				textcoord(canvas, ex, ey, endcolor, cfg)
				textcoord(canvas, cx, cy, shapecolor, cfg)
				r, a2, a1 := arcElements()
				for t := a1; t < a2; t += math.Pi / 256 {
					px, py := canvas.Polar(bx, by, r, float32(t))
					canvas.Line(bx, by, px, py, cfg.linesize, cfg.shapecolor)
				}
			}
			kbpointer(e.Source, cfg)
			cx, cy = mouseX, mouseY
			e.Frame(canvas.Context.Ops)
		}
	}
}