Add example showing Metal and Gtk4 integration (#106)

[skip ci]

examples/gtk.jl

@@ -0,0 +1,53 @@
+# EXCLUDE FROM TESTING
+"""
+This example demonstrates how to integrate Metal and Gtk4. 
+An image is generated using a Metal kernel and efficiently displayed using Gtk4
+"""
+
+using Pkg, Metal
+metal_dir = dirname(@__DIR__)
+
+Pkg.activate(; temp=true)
+Pkg.add(["Gtk4", "Colors", "FixedPointNumbers"])
+Pkg.develop(path=metal_dir)
+
+using Colors, FixedPointNumbers, Gtk4, Metal
+
+if !isinteractive()
+    Gtk4.GLib.start_main_loop()
+end
+
+function generate(img, pos)
+    r, c = Int32.(size(img))
+    i,j = thread_position_in_grid_2d()
+    @inbounds if i <= r && j <= c
+        img[i,j] = pos < j < pos + 10 ? colorant"red" : colorant"thistle"
+    end
+    return
+end
+
+img = MtlArray{RGB{N0f8}}(undef, 800,600)
+host = unsafe_wrap(Array{RGB{N0f8}}, img, size(img))
+
+## initial image
+Metal.@sync @metal threads=16,16 grid=size(img) generate(img, 0)
+
+win = GtkWindow("Test", 800, 600);
+
+data = reinterpret(Gtk4.GdkPixbufLib.RGB, host) 
+pixbuf = Gtk4.GdkPixbufLib.GdkPixbuf(data,false) 
+view = GtkImage(pixbuf)
+
+push!(win,view)
+
+for i=1:400
+    Metal.@sync @metal threads=16,16 grid=size(img) generate(img, i*2)
+    #forces redraw without copy
+    Gtk4.G_.set_from_pixbuf(view, pixbuf)
+    sleep(0.01)
+    win.visible || break
+end
+
+if !isinteractive()
+    !win.visible || Gtk4.GLib.waitforsignal(win,:close_request)
+end