commit 58b1904e3eec4d80a9a30e4267d902b523351aec
from: Russ Cox <rsc@swtch.com>
date: Mon Nov 26 04:55:27 2012 UTC

devdraw: fake dpi calculation on Mac

R=rsc
http://codereview.appspot.com/6782115

commit - cc9547960e7cf12129e84c9489eb5dcd6235144b
commit + 58b1904e3eec4d80a9a30e4267d902b523351aec
blob - c6389e9ba8bc1d7f562bd95c750a7dad92c7aac8
blob + f77186129fde313b2f6422b2b34d7f33bc8dcc21
--- src/cmd/devdraw/cocoa-screen.m
+++ src/cmd/devdraw/cocoa-screen.m
@@ -396,6 +396,14 @@ initimg(void)
 	[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;
 }