target-bsnes: Do not set the window background to black.

To resize a window on X11, the window manager tells the X11 server to change the
window size, then the X11 server tells the application to paint itself, and then
(eventually) the application tells the X11 server what to draw. This adds an
arbitrary amount of latency to resizing, so to make things feel more responsive,
the X11 server will paint any newly-exposed parts of the window with a default
background colour. If it happens to be the same colour as the appplication would
paint anyway, this gives resizing a much better user-experience.

Since most of bsnes' window is occupied by the viewport, which is always black,
bsnes accordingly set its window background colour to black for the best
resizing experience. However, this had two additional effects:

  - When no game is loaded, bsnes displays the bsnes icon in the main display
    area. Black canvas widgets are used as spacers to position the icon
    correctly, but the spacers don't cover the entire background, and the window
    background shines through.
  - GTK+3 draws widget transparent by default, so the background colour of the
    parent widget shines through child widgets. In particular, setting the
    window background to black makes the menu background black, even if the menu
    text is also a dark colour.

In order to get the menu to display properly in GTK+3 builds, we have to stop
bsnes from setting the top-level window background colour, and we also have to
ensure that the spacer widgets around the icon cover the entire surface of the
window.

Fixes #108.

bsnes/target-bsnes/presentation/presentation.cpp

@@ -218,6 +218,10 @@ auto Presentation::create() -> void {
   iconCanvas.setDroppable();
   iconCanvas.onDrop([&](auto locations) { onDrop(locations); });
 
+  iconPadding.setColor({0, 0, 0});
+  iconPadding.setDroppable();
+  iconPadding.onDrop([&](auto locations) { onDrop(locations); });
+
   if(!settings.general.statusBar) layout.remove(statusLayout);
 
   auto font = Font().setBold();
@@ -250,7 +254,6 @@ auto Presentation::create() -> void {
   });
 
   setTitle({"bsnes v", Emulator::Version});
-  setBackgroundColor({0, 0, 0});
   resizeWindow();
   setAlignment(Alignment::Center);
 

bsnes/target-bsnes/presentation/presentation.hpp

@@ -126,7 +126,9 @@ struct Presentation : Window {
       Viewport viewport{&viewportLayout, Size{~0, ~0}, 0};
       VerticalLayout iconLayout{&viewportLayout, Size{0, ~0}, 0};
         Canvas iconSpacer{&iconLayout, Size{144, ~0}, 0};
-        Canvas iconCanvas{&iconLayout, Size{128, 128}, 0};
+        HorizontalLayout iconHorizontal{&iconLayout, Size{144, 128}, 0};
+          Canvas iconCanvas{&iconHorizontal, Size{128, 128}, 0};
+          Canvas iconPadding{&iconHorizontal, Size{16, 128}, 0};
     HorizontalLayout statusLayout{&layout, Size{~0, StatusHeight}, 0};
       Label spacerIcon{&statusLayout, Size{8, ~0}, 0};
       Canvas statusIcon{&statusLayout, Size{16, ~0}, 0};