Postprocessing example broken

[porglezomp]

The postprocessing example fails with "bad argument #1 to 'fill' (Texture expected, got userdata)".

This part can be fixed with a two-line change.

 local function fullScreenDraw(source)
-  lovr.graphics.fill(source)
+  lovr.graphics.fill(source:getTexture())
 end

 -- ...

     screenShader:send("direction", {0, 4})
-    lovr.graphics.fill(tempCanvas[2]) -- On the final pass, render directly to the screen.
+    lovr.graphics.fill(tempCanvas[2]:getTexture()) -- On the final pass, render directly to the screen.
   end

Unfortunately (at least in the local viewer app on macOS) it renders completely incorrectly, flickering and horizontally duplicating the scene 16 or so times, presumably due to the double-wide texture rendering with the canvas.

• macOS 10.14.6 • LOVR 0.13.0 (Very Velociraptor) • Intel Iris Graphics 6100 1536 MB

[bjornbytes]

This should be working much better now and handle differences between platforms. Still testing on all the devices I can get access to.