Does the iPhone support this feature, and does it support rendering a texture with an alpha channel?
I am doing the research for a project that involves a cityscape, and I am wondering if an imposter system is feasible using Unity.
rendering a texture with alpha is possible.
RenderTextures don’t exist. The iPhone GPU is a pure fixed function pipeline hardware (comparable to 1999 / 2000 hardware, NVIDIA TNT2 / GeForce1)
Is that right?
OpenGL ES does define http://www.khronos.org/registry/gles/extensions/OES/OES_framebuffer_object.txt
Is this not supported on iPhone?
How does one render to a texture on the iPhone?
here is game like use render to a texture on the iPhone
<-please look this pic,outburst effect use bump map. and It seems that screen have post process effict(bloom or soften)
here is link
http://www.apex-designs.net/payback_screens.html
Make in Unity3D???
No that is ported from GP2x from developers with a few year of experience developing on no end hardware (the 1999 class gpu on the iphone is not even low end as even intel is significantly faster ^^)
Unity does not have RenderTargets on the iPhone.
If you want to use 100% of what iphone can you must program your own technology.
Post render effects do not needfully require render to texture by the way, you can do that by just having good art.
bump mapping does not exist on iphone. What exists is Dot3 normal mapping, which you can use as well in unity if you want. But you have to keep in mind that it takes a serious amount of performance and that it is not per pixel calculated as shader driven normalmapping is, simply because lights only affect vertices, not pixels.
I’m going slightly offtopic, but the above is not true. There’s no difference between some mythical “shader driven normal mapping” and Dot3 bump mapping that is on the iPhone. It’s the same operations. (I’m not saying using Dot3 on the iPhone is practical)
I thought the iPhone has no pixel shaders.
That would mean that lights are hardware lights, which operate on vertices and only interpolate the light data along the triangles.
This assumption was / is backed up by the fact that Unity dublicates the geometry if you use non-directional lights, as well as as section 2.12.1 of the opengl es 1.1 specs.
Is the reason behind the geometry dublication that unity uses it to apply a “per pixel light texture” thats generated in realtime?
That would then give shader comparable Normalmapping and would naturally be an interesting approach for artistic effects 
but otherwise, if it is pure geometry, the difference is significant, as the normal effect is not dependant on the pixel light data but the interpolated vertex light data.
small triangles don’t show the problem, but larger triangles especially in combinations of concave and convex geometry do so pretty well.
We already discussed this in another thread, on exact this topic. Somewhere starting here.
Diffuse lighting is a dot(normal,lightDirection) operation. Fixed function hardware lights do this on the vertices. If you don’t use fixed function hardware lights, but instead do this operation on the pixels (via combiner or pixel shader), you have pixel lighting. This is possible on the iPhone.
What?
But this is getting offtopic really fast.
agreed on OT, so created a new thread here: http://forum.unity3d.com/viewtopic.php?p=118578
So the conclusion is that it is not possible to use imposters from within Unity?
due to the implication of imposters (another render pass → at half the FPS per imposter if it is updated each frame), imposters even with rendertextures wouldn’t really be an option.
Its after all a phone, not a pc, even crappy intel integrated beat it by 30 : 1 and already those can get some nice perf problems with imposters.
Well, from what I can tell, render-to-texture is possible using iPhone OpenGL ES.
As for the implications; I think the game urashima posted a link to illustrates the successful use of imposters on a handheld game. There are several academic papers on the web illustrating their use on handhelds as well.
It would be good if Unity was able to help me achieve the use of imposters.
It’s Payback iPhone/iPod Touch Official Video
this game has hdr lighting…orz