camera example from https://github.com/elliotmr/tmx/tree/master/pixeltmx/example

mouse_zoom.go

	cameraOrigin := pixel.ZV.Add(win.Bounds().Center())
	scale := 1.0
	dragOrigin := pixel.V(0, 0)
	second := time.Tick(time.Second)
	viewMatrix := pixel.IM
	frames := 0
	for !win.Closed() {
		if win.MouseScroll().Y != 0 {
			factor := math.Pow(1.2, win.MouseScroll().Y)
			zoomDeltaStart := viewMatrix.Unproject(win.MousePosition())
			scale *= factor
			cameraOrigin = zoomDeltaStart.Add(win.Bounds().Center().Sub(win.MousePosition().Scaled(1 / scale)))
		}
		if win.JustPressed(pixelgl.MouseButton1) {
			dragOrigin = win.MousePosition().Scaled(1 / scale)
		} else if win.Pressed(pixelgl.MouseButton1) {
			newOrigin := win.MousePosition().Scaled(1 / scale)
			cameraOrigin = cameraOrigin.Sub(newOrigin.Sub(dragOrigin))
			dragOrigin = newOrigin
		}
		viewMatrix = pixel.IM.Moved(win.Bounds().Center().Sub(cameraOrigin)).Scaled(pixel.ZV, scale)