iPhone original render faster than iPhone 3GS? - iphone

Question

I'm working on a game on iPhone, which uses C++ and OpenGL ES 1.x library.
It works fine on simulator. But when I install it on real iPhone, I found out that on iPhone original, it took about 20 milliseconds to render a frame. However, it took 35~40 milliseconds to render a frame on iPhone 3GS.
I've tried various OS, including 3GS + iOS 3.1.2, 3G + iOS 4.0, 3GS + iOS 4.1, iPad + iOS 3.2. All of them render much slower than iPhone original, which sounds really ridiculous to me. I tried google for anything I can think of, fixing every problem it might be related to, but nothing changed.
I have 2 machine which these pieces of code render faster: 1) iPhone original with iOS 3.1.3, 2) iPod Touch with iOS 3.1.3. Both took about 20 milliseconds to render a frame.
And 4 machine which render mysteriously slower: 1) iPhone 3G with iOS 4.0, 2) iPhone 3GS with iOS 3.1.2, 3) iPhone 3GS with iOS 4.1, 4) iPad with iOS 3.2. iPhone took about 35-40 milliseconds to render a frame and iPad took around 25.
I use PVRTC for texture, which is first cooked and make into a bundle. It uses total of ten 512x512 textures, three 1024x1024 textures.
The piece of code which binding texture is as follow:
GLenum internalFormat = 0;
GLenum pixelType = 0;
// resolve type
ResetFlags_();
assert(2==attr.Dimension && 1==attr.Depth);
switch (attr.Format)
{
case FORMAT_PVRTC2:
assert(attr.Width==attr.Height);
if (attr.AlphaBits>0)
internalFormat = GL_COMPRESSED_RGBA_PVRTC_2BPPV1_IMG;
else
internalFormat = GL_COMPRESSED_RGB_PVRTC_2BPPV1_IMG;
break;
case FORMAT_PVRTC4:
assert(attr.Width==attr.Height);
if (attr.AlphaBits>0)
internalFormat = GL_COMPRESSED_RGBA_PVRTC_4BPPV1_IMG;
else
internalFormat = GL_COMPRESSED_RGB_PVRTC_4BPPV1_IMG;
break;
... other formats ...
}
// prepare temp buffer to load
MemoryBuffer tmpBuffer(true);
uint8* buffer = tmpBuffer.GetWritePtr(attr.TextureSize);
// read data
stream.Read(buffer, attr.TextureSize);
if (stream.Fail())
return false;
// init
width_ = attr.Width;
height_ = attr.Height;
LODs_ = attr.LODs;
alphaBits_ = attr.AlphaBits;
// create and upload texture
glGenTextures(1, &glTexture_);
glBindTexture(GL_TEXTURE_2D, glTexture_);
uint32 offset = 0;
uint32 dim = width_; // = height
uint32 w, h;
switch (internalFormat)
{
case GL_COMPRESSED_RGBA_PVRTC_2BPPV1_IMG:
case GL_COMPRESSED_RGB_PVRTC_2BPPV1_IMG:
case GL_COMPRESSED_RGBA_PVRTC_4BPPV1_IMG:
case GL_COMPRESSED_RGB_PVRTC_4BPPV1_IMG:
for (uint32 i=0; i<LODs_; ++i) {
assert(offset<attr.TextureSize);
w = dim >> ((FORMAT_PVRTC2==attr.Format) ? 3:2);
h = dim >> 2;
// Clamp to minimum number of blocks
if (w<2) w = 2;
if (h<2) h = 2;
uint32 const image_size = w * h * 8; // 8 bytes for each block
glCompressedTexImage2D(GL_TEXTURE_2D, i, internalFormat, dim, dim, 0, image_size, buffer+offset);
dim >>= 1;
offset += image_size;
break;
... other formats ...
}
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST); // tri-linear?
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
SetContext_(&glTexture_);
return true;
Rendering part is huge because it uses an engine developed by others. As far as I can tell, it uses glDrawArrays and no shader was used.
Anyone had encounter the same problem before? I really can't see why iPhone original render much faster than iPhone 3GS.
p.s. I forgot to say. I draw only 2D rectangles with textures only. And it's around 20 rectangles in my game ( one background and one UI with 480x360 size. Others are commonly 64x64 units.)

Answer 1

The behaviour you are getting could be because of the possible emulation of Fixed Function Pipeline (FFP) via Programmable Pipeline (i.e. shaders).
Can you please execute a test that will load and display your textures in some way, completely without your engine.