Add IsFingerDown boolean to the Event object

IsFingerDown will be true as long as at least one finger has registered
a TouchDown event but not yet a TouchUp. The calling program can check
this boolean to distinguish a mouse movement from a physical mouse to a
probable touch based swipe.

event/event.go

@@ -34,13 +34,19 @@ type State struct {
 	WindowResized bool
 
 	// Touch state
-	Touching        bool
+	Touching        bool // A touch event this tick
 	TouchNumFingers int
 	TouchCenterX    int
 	TouchCenterY    int
 	GestureRotated  float64
 	GesturePinched  float64
 
+	// Will be true if at least one finger is currently still held down on
+	// a touch screen. Meaning a FingerDown event happened in the past, but
+	// not yet a FingerUp event. If IsFingerDown, you can extrapolate that
+	// mouse movement events were actually touch swipes and not a mouse.
+	IsFingerDown bool
+
 	// Game controller events.
 	// NOTE: for SDL2 you will need to call GameControllerEventState(1)
 	// from veandco/go-sdl2/sdl for events to be read by SDL2.

sdl/events.go

@@ -24,7 +24,7 @@ func (r *Renderer) Poll() (*event.State, error) {
 
 	// Reset some events.
 	s.WindowResized = false
-	// s.Touching = false
+	s.Touching = false
 
 	// helper function to push keyboard key names on keyDown events only.
 	pushKey := func(name string, state uint8) {
@@ -108,6 +108,25 @@ func (r *Renderer) Poll() (*event.State, error) {
 					t.Timestamp, sdl.GetTicks(), t.Type, t.Which, t.X, t.Y,
 				)
 			}
+		case *sdl.TouchFingerEvent:
+			if DebugTouchEvents {
+				fmt.Printf("[%d ms] tick:%d TouchFinger  type:%d  Finger=%d  TouchID=%+v  Pressure=%f  XY=%f,%f\n",
+					t.Timestamp, sdl.GetTicks(), t.Type, t.FingerID, t.TouchID, t.Pressure, t.X, t.Y,
+				)
+			}
+			s.Touching = true
+			s.TouchNumFingers = 1
+			s.TouchCenterX = int(t.X)
+			s.TouchCenterY = int(t.Y)
+
+			// Track which finger(s) are down or up.
+			if t.Type == sdl.FINGERDOWN {
+				r.fingersDown[t.FingerID] = nil
+			} else if t.Type == sdl.FINGERUP {
+				delete(r.fingersDown, t.FingerID)
+			}
+
+			s.IsFingerDown = len(r.fingersDown) > 0
 		case *sdl.MultiGestureEvent:
 			if DebugTouchEvents {
 				fmt.Printf("[%d ms] tick:%d MultiGesture  type:%d  Num=%d  TouchID=%+v  Dt=%f  Dd=%f  XY=%f,%f\n",

sdl/sdl.go

@@ -28,6 +28,12 @@ type Renderer struct {
 	textures  map[string]*Texture // cached textures
 	textureMu sync.RWMutex
 
+	// Touch screens: track which finger(s) are currently down, if one finger is
+	// down then the events.IsFingerDown will be true. The calling program can
+	// tell whether a MouseMove event is a mouse or a finger swipe if it happens
+	// while IsFingerDown is set.
+	fingersDown map[sdl.FingerID]interface{}
+
 	// Optimizations to minimize SDL calls.
 	lastColor render.Color
 }
@@ -35,11 +41,12 @@ type Renderer struct {
 // New creates the SDL renderer.
 func New(title string, width, height int) *Renderer {
 	return &Renderer{
-		events:   event.NewState(),
-		title:    title,
-		width:    int32(width),
-		height:   int32(height),
-		textures: map[string]*Texture{},
+		events:      event.NewState(),
+		title:       title,
+		width:       int32(width),
+		height:      int32(height),
+		textures:    map[string]*Texture{},
+		fingersDown: map[sdl.FingerID]interface{}{},
 	}
 }