Regarding iPad alpha's

Unity Engine
,
1

I know alpha’s don’t play well with iPad but if I use Trasnparent-CutOut, does it run better?

Thanks,
-Mike Berger

2

even worse

alpha test is by definition slower than alpha blend on the iphone so you get the overdraw hit from alpha + the alpha test hit

3

So, what’s the best option here?

4

use meshes with appropriate UV maps instead of using alpha for the cutout

5

That makes sense. So I guess gradients are just impossible?

Thanks,
-Mike

6

The problem is fill rate. If you can minimize the amount of pixels that need to be blended, you’ll do better, as long as the polycount isn’t drastically increased. What is the shape you’re trying to use? Maybe you can cut into it a bit instead of using chunky quads. And maybe you can use an opaque shader for part of the mesh, and a blended one elsewhere. (This is reasonable, considering draw calls are aided by the iPad’s faster CPU.)

You can also use an alpha test (cutout) shader outside of the geometry queue, which will yield better performance on the iPad. (None of the builtin shaders do this.)

7

If I had to relate it to another game I’d say Geometry Wars Touch for iPad would be closest. Grids and glowing stuff.

8

I keep seeing people complaining about the iPad alpha management…

Given the same game with the same alphatest use, but with increased resolution for iPad, please tell me the iPad is not slower than a 3GS, at least ?

9

My game “Retro Revolution” runs very smooth on my 3GS with no fps drops, I ported it over to my iPad with no changes but the screen size and I get single digit fps. It is unplayable. Now, it did have an alpa cover nearly the entire screen (when you get hit the tunnel fades red. The opacity depended on the amount of health the player had). When I removed that alpha it run much better but when you run over the floor modifiers the fps drops down.

So, currently, I am creating an entirely new game for iPad.

-Mike

10

It will be seriously slower.

The ipad has the same graphics chip as the 3GS but 5.2 times as many pixels which means it has 1/5.2 times as much fillrate available than the 3GS. Or put in different numbers:

While the original iphone could redraw the screen 4-5 times (pixel number wise) for fluent FPS, you can do so only 2-3 times on the iPad

If you overdraw the whole screen with alpha grids, you can draw one background and 1-2 fullscreen grids and your fps will start to play submarine.

I’m hoping that UT might come up with a Unity iphone 1.7.1 which supports SetResolution (assuming it does not right now) so you can render at a lower resolution and let the eaglview scale it up. Thats the only way to technically overcome the problem.

11

Oh sh- …

That’s really, really bad news. I thought the faster processor could fill the gap :?

12

p.s : LOL @ iPad built for gaming. :lol:

So what we got is only a very huge iPhone, litterally, as we can’t really make profit of the larger screen resolution.

Lame …

13

Do sprites using SM2 or the GUImanagers have this same alpha performance liability?

14

2D in general is on the “dark side” right from the start as they need to use alpha pixels to cut part of the image visually.

With real geometry you can cut the parts of the image without overdrawing the pixels, but with images you have alpha there and those pixels are rendered independent on if they are seen or not (non-alpha pixels that are not seen are not drawn by the iphone gpu and thus don’t impact the fillrate that heavily at all)

As such 3D models or the 2D authoring that was used on Zombieville and alike is a much more ipad optimal approach

15

So on a scale of 1-10 with 10 being the worst for performance how would the following rate?

  1. Alpha mapped Black and White,game HUD using a GUImanager

  2. Grey Scaled(ie gradient) Alpha, game HUD using a GUImanager

  3. 3D Texture map with a Black and White Alpha map

  4. 3D Texture map with a Grey Scaled Alpha

16

  1. There is no 3D texture on any unity :slight_smile:

    1. and 3) are worse because they are not just alpha blending but also alpha test which is less performant than just alpha blend on idevices
17

I meant a 3D models texture map as opposed to a plane. I imagine moving 3D models with alpha maps are more complex than a plane that remains still.

18

a plane is a 3d model too.
There is no difference in it.

The only thing that matters is the amount of alphaed pixels that are drawn over non-alpha pixels (-> redrawn pixels), independent of the actual alpha value

19

Yup, I understand the versatility ^^

But here Apple just made a bad move with iPad’s hardware, as it offers double the resolution, but not double the GPU power … Thus promising users to have the same games as on iPhone, and asking devs to ramp that resolution up in their game, they just proved once again that they don’t have a single clue about real gamemaking. :slight_smile: