iPad missing OpenGL extension string GL_APPLE_texture_2D_limited_npot

Question

In my iOS game, I want to use the GL_APPLE_texture_2D_limited_npot extension when available to save memory (the game have NPOT textures, and in my current implementation I add some padding to make those power of two).

I am testing in my iPad (first generation). Every thing I have read so far says that all iOS devices which supports OpenGLES2 (including iPad) also support GL_APPLE_texture_2D_limited_npot (which is very good, since my game use OpenGLES2). I have tested in my iPad, and it does support (I removed the padding and the images work if I set wrap to GL_CLAMP_TO_EDGE), but the extension does not show when I call glGetString(GL_EXTENSIONS). The code:

const char *extensions = (const char *)glGetString(GL_EXTENSIONS);
std::cout << extensions << "\n";

Results in:

GL_OES_depth_texture GL_OES_depth24 GL_OES_element_index_uint GL_OES_fbo_render_mipmap GL_OES_mapbuffer GL_OES_packed_depth_stencil GL_OES_rgb8_rgba8 GL_OES_standard_derivatives GL_OES_texture_float GL_OES_texture_half_float GL_OES_vertex_array_object GL_EXT_blend_minmax GL_EXT_debug_label GL_EXT_debug_marker GL_EXT_discard_framebuffer GL_EXT_read_format_bgra GL_EXT_separate_shader_objects GL_EXT_shader_texture_lod GL_EXT_texture_filter_anisotropic GL_APPLE_framebuffer_multisample GL_APPLE_rgb_422 GL_APPLE_texture_format_BGRA8888 GL_APPLE_texture_max_level GL_IMG_read_format GL_IMG_texture_compression_pvrtc

Why does this extension does not show with glGetString(GL_EXTENSIONS)? What is the proper way to check for it? Does all OpenGLES2 iOS devices really support it?

Answer 1

OpenGL ES 2.0 supports non power of 2 textures in specification. There is no need for extension. Here is the spec: http://www.khronos.org/registry/gles/specs/2.0/es_full_spec_2.0.25.pdf (Page 69):

If wt and ht are the specified image width and height, and if either wt or ht are less than zero, then the error INVALID_VALUE is generated. The maximum allowable width and height of a two-dimensional texture image must be at least 2k-lod for image arrays of level zero through k, where k is the log base 2 of MAX_TEXTURE_SIZE. and lod is the level-of-detail of the image array. It may be zero for image arrays of any level-of-detail greater than k. The error INVALID_VALUE is generated if the specified image is too large to be stored under any conditions.

Not a word about power of two restriction (that is in OpenGL ES 1.x standard).

And if you read the specification of extension - http://www.khronos.org/registry/gles/extensions/APPLE/APPLE_texture_2D_limited_npot.txt, then you'll notice that it is written agains OpenGL ES 1.1 spec.