set a limit on how far in a ZoomRegion can be zoomed (#61)

* set a limit on how far in a ZoomRegion can be zoomed

Prevents an InexactError and also prevents getting stuck at a high zoom level.

* minor tweaks

* force scroll event controller to emit discrete scroll events

The `MouseScroll` object only handles scroll direction, not a step size.
In the future, we should consider adding that.

This makes scrolling with a trackpad a bit less touchy (at least on my
laptop).

* bump version

* use alternative approach

Project.toml

@@ -1,6 +1,6 @@
 name = "GtkObservables"
 uuid = "8710efd8-4ad6-11eb-33ea-2d5ceb25a41c"
-version = "2.0.3"
+version = "2.0.4"
 
 [deps]
 Cairo = "159f3aea-2a34-519c-b102-8c37f9878175"

src/graphics_interaction.jl

@@ -240,7 +240,8 @@ struct MouseHandler{U<:CairoUnit}
         g = GtkGestureClick(canvas,0)
         gm = GtkEventControllerMotion(canvas)
         gs = GtkEventControllerScroll(Gtk4.EventControllerScrollFlags_HORIZONTAL |
-                                      Gtk4.EventControllerScrollFlags_VERTICAL , canvas)
+                                      Gtk4.EventControllerScrollFlags_VERTICAL  |
+                                      Gtk4.EventControllerScrollFlags_DISCRETE , canvas)
 
         push!(ids, signal_connect(mousedown_cb, g, "pressed", Nothing, (Int32, Float64, Float64), false, handler))
         push!(ids, signal_connect(mouseup_cb, g, "released", Nothing, (Int32, Float64, Float64), false, handler))
@@ -515,6 +516,9 @@ function zoom(zr::ZoomRegion, s, pos::XY)
     w, h = IntervalSets.width(xview), IntervalSets.width(yview)
     fx, fy = (centerx-minimum(xview))/w, (centery-minimum(yview))/h
     wbb, hbb = s*w, s*h
+    # set a limit on how far in we can zoom (ImageView issue #297)
+    wbb = (wbb<2.0) ? 2.0 : wbb
+    hbb = (hbb<2.0) ? 2.0 : hbb
     xview = interior(ClosedInterval(centerx-fx*wbb,centerx+(1-fx)*wbb), xviewlimits)
     yview = interior(ClosedInterval(centery-fy*hbb,centery+(1-fy)*hbb), yviewlimits)
     ZoomRegion(zr.fullview, XY(xview, yview))

test/runtests.jl

@@ -558,6 +558,19 @@ Base.axes(::Foo) = (Base.OneTo(7), Base.OneTo(9))
     @test zrz.currentview.y == 16..55
     zrr = GtkObservables.reset(zrz)
     @test zrr == zr
+
+    # ImageView #297
+    # When we have zoomed so far in that the region is less than three
+    # pixels wide, do not zoom in further. This prevents a truncation error
+    # when the new interval width is 0 and also prevents getting "stuck" at
+    # that zoom level (since zooming back out doesn't work when the current
+    # interval width is zero).
+    zrn = ZoomRegion((1:5,1:5))
+    c = XY(UserUnit(3),UserUnit(3))
+    zrz = zoom(zrn, 0.5)
+    @test zrz.currentview.x == 2..4
+    zrz = zoom(zrz, 0.5)
+    @test zrz.currentview.x == 2..4
 
     zrbb = ZoomRegion(zr.fullview, BoundingBox(5, 15, 35, 75))
     @test zrbb.fullview === zr.fullview