devdraw: fake dpi calculation on Mac
R=rsc
http://codereview.appspot.com/6782115
diff --git a/src/cmd/devdraw/cocoa-screen.m b/src/cmd/devdraw/cocoa-screen.m
index c6389e9..f771861 100644
--- a/src/cmd/devdraw/cocoa-screen.m
+++ b/src/cmd/devdraw/cocoa-screen.m
@@ -396,6 +396,14 @@
[win.img setSize: ptsize];
win.topixelscale = size.width / ptsize.width;
win.topointscale = 1.0f / win.topixelscale;
+
+ // NOTE: This is not really the display DPI.
+ // On retina, topixelscale is 2; otherwise it is 1.
+ // This formula gives us 220 for retina, 110 otherwise.
+ // That's not quite right but it's close to correct.
+ // http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density#Apple
+ displaydpi = win.topixelscale * 110;
+
return i;
}
