don't open windows during precompilation

src/graphics_interaction.jl

@@ -269,8 +269,8 @@ struct Canvas{U}
     mouse::MouseHandler{U}
     preserved::Vector{Any}
 
-    function Canvas{U}(w::Int=-1, h::Int=-1; own::Bool=true) where U
-        gtkcanvas = GtkCanvas(w, h)
+    function Canvas{U}(w::Int=-1, h::Int=-1; own::Bool=true, init_back=false) where U
+        gtkcanvas = GtkCanvas(w, h, init_back)
         # Initialize handlers
         mouse = MouseHandler{U}(gtkcanvas)
         grab_focus(gtkcanvas)
@@ -280,7 +280,7 @@ struct Canvas{U}
         canvas
     end
 end
-Canvas{U}(w::Integer, h::Integer=-1; own::Bool=true) where U = Canvas{U}(Int(w)::Int, Int(h)::Int; own=own)
+Canvas{U}(w::Integer, h::Integer=-1; own::Bool=true, init_back = false) where U = Canvas{U}(Int(w)::Int, Int(h)::Int; own=own, init_back=init_back)
 
 Base.show(io::IO, canvas::Canvas{U}) where U = print(io, "GtkObservables.Canvas{$U}()")
 
@@ -292,8 +292,8 @@ width `w` and height `h`. `U` refers to the units for the canvas (for
 both drawing and reporting mouse pointer positions), see
 [`DeviceUnit`](@ref) and [`UserUnit`](@ref). See also [`GtkObservables.Canvas`](@ref).
 """
-canvas(::Type{U}=DeviceUnit, w::Integer=-1, h::Integer=-1) where {U<:CairoUnit} = Canvas{U}(w, h)
-canvas(w::Integer, h::Integer) = canvas(DeviceUnit, w, h)
+canvas(::Type{U}=DeviceUnit, w::Integer=-1, h::Integer=-1; init_back=false) where {U<:CairoUnit} = Canvas{U}(w, h; init_back=init_back)
+canvas(w::Integer, h::Integer; init_back=false) = canvas(DeviceUnit, w, h; init_back=init_back)
 
 """
     draw(f, c::GtkObservables.Canvas, signals...)

src/precompile.jl

@@ -106,13 +106,9 @@ using PrecompileTools
         dtw=nothing
 
         # canvas
-        win=GtkWindow()
         try # if we don't have a display, this might fail?
             for U in (UserUnit, DeviceUnit)
-                c = canvas(U, 100, 100)
-                win[] = widget(c)
-                show(win)
-                sleep(1.0)  # allow canvas to be realized
+                c = canvas(U, 100, 100; init_back=true)
                 fill!(c, RGB(0, 0, 0))
                 fill!(c, RGBA(1, 1, 1, 1))
                 lastevent = Ref("nothing")
@@ -128,9 +124,7 @@ using PrecompileTools
                     stroke(ctx)
                 end
             end
-            c = canvas(UserUnit)
-            win[] = widget(c)
-            sleep(1.0)  # allow canvas to be realized
+            c = canvas(UserUnit, 100, 100; init_back=true)
             zr = Observable(ZoomRegion((1:11, 1:20)))
             zoomrb = init_zoom_rubberband(c, zr)
             zooms = init_zoom_scroll(c, zr)
@@ -156,10 +150,10 @@ using PrecompileTools
             #            eventscroll(c, UP, UserUnit(8), UserUnit(4), CONTROL))
             signal_emit(scrollcontroller(c), "scroll", Bool,
                         convert(Float64, UserUnit(8)), convert(Float64, UserUnit(4)))
+            c=nothing
         catch
             @warn("GtkObservables canvas precompile code failure")
         end
-        destroy(win)
     end
 end