From 803e42714ec9c6388919a3ad547f41d0dd9752a1 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sun, 30 Sep 2018 17:08:16 +0900
Subject: [PATCH] input: Implement wheel event on browsers

Fixes #630
---
 internal/input/input_js.go | 15 +++++++++++++--
 internal/ui/ui_js.go       |  4 ++--
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/internal/input/input_js.go b/internal/input/input_js.go
index 5712554dd..39ced91b4 100644
--- a/internal/input/input_js.go
+++ b/internal/input/input_js.go
@@ -35,6 +35,8 @@ type Input struct {
 	mouseButtonPressed map[int]bool
 	cursorX            int
 	cursorY            int
+	wheelX             float64
+	wheelY             float64
 	gamepads           [16]gamePad
 	touches            []*Touch
 	runeBuffer         []rune
@@ -49,6 +51,11 @@ func (i *Input) ClearRuneBuffer() {
 	i.runeBuffer = nil
 }
 
+func (i *Input) ResetWheelValues() {
+	i.wheelX = 0
+	i.wheelY = 0
+}
+
 func (i *Input) IsKeyPressed(key Key) bool {
 	if i.keyPressed != nil {
 		for _, c := range keyToCodes[key] {
@@ -92,8 +99,7 @@ func (i *Input) IsMouseButtonPressed(button MouseButton) bool {
 }
 
 func (i *Input) Wheel() (xoff, yoff float64) {
-	return 0, 0
-	// TODO: Mouse scroll functionality is not yet implemented in js
+	return i.wheelX, i.wheelY
 }
 
 func (i *Input) keyDown(code string) {
@@ -241,6 +247,11 @@ func OnMouseMove(e js.Value) {
 	setMouseCursorFromEvent(e)
 }
 
+func OnWheel(e js.Value) {
+	theInput.wheelX = e.Get("deltaX").Float()
+	theInput.wheelY = e.Get("deltaY").Float()
+}
+
 func OnTouchStart(e js.Value) {
 	theInput.updateTouches(e)
 }
diff --git a/internal/ui/ui_js.go b/internal/ui/ui_js.go
index cb78217f2..37afdc500 100644
--- a/internal/ui/ui_js.go
+++ b/internal/ui/ui_js.go
@@ -207,8 +207,7 @@ func (u *userInterface) update(g GraphicsContext) error {
 	u.updateGraphicsContext(g)
 	if err := g.Update(func() {
 		input.Get().ClearRuneBuffer()
-		// TODO: insert ResetScrollValues() counterpart to 'ui_glfw.go' here
-		// The offscreens must be updated every frame (#490).
+		input.Get().ResetWheelValues()
 		u.updateGraphicsContext(g)
 	}); err != nil {
 		return err
@@ -322,6 +321,7 @@ func init() {
 	canvas.Call("addEventListener", "mousedown", js.NewEventCallback(js.PreventDefault, input.OnMouseDown))
 	canvas.Call("addEventListener", "mouseup", js.NewEventCallback(js.PreventDefault, input.OnMouseUp))
 	canvas.Call("addEventListener", "mousemove", js.NewEventCallback(js.PreventDefault, input.OnMouseMove))
+	canvas.Call("addEventListener", "wheel", js.NewEventCallback(js.PreventDefault, input.OnWheel))
 
 	// Touch
 	canvas.Call("addEventListener", "touchstart", js.NewEventCallback(js.PreventDefault, input.OnTouchStart))