understanding the differences between the mobile and desktop renderers

Check out the attached imgur post, the first one is SM5 and the second is SM4 and the third is iOS Mobile Preview. Notice how the grass the mobile render is noticeably thinner than the grass in the SM4 and SM5 renders. Does anybody know what is causing the grass to have so much more perceived volume in the SM4/5 renders?

If somebody could explain the color differences as well I would also be very interested.

SM4 and SM5 support temporal antialiasing, which works on textures and masked transparencies, causing the grass to look fuller since it allows more samples to be used to build the final image. On iOS only MSAA is supported which doesn’t work on textures and thus masked transparencies will become thinner further from the camera. You can see the same result in SM4/5 if you disable antialiasing. To work around that you need to play with the mipmap settings, to try to make your masks become “thicker” at the smaller mips.

Color differences are mostly due to mobile using a different and simpler tone mapper (the shader that converts the rendered HDR values into LDR colors that can be displayed on the screen).

So all the grass in the photos is using individually modeled blades - there is no transparency at all, every material is opaque. Could all of the differences be explained because of the simpler tone mapper?

Ah, since the blades were parallel it did look like masked planes. The temporal AA should have the same effect on “thin” geometry like that.

Ah yeah that did it! I disabled AA in the SM5 renderer and the results were basically the same as the mobile renderer, minus the color differences. Cheers!