+ void *odata = backbuffer_data;
+ size_t olen = backbuffer_len;
+
+# if !defined __OPTIMIZE__ || TARGET_IPHONE_SIMULATOR
+ NSLog(@"backbuffer %.0fx%.0f",
+ new_size.width, new_size.height);
+# endif
+
+ /* OS X uses APPLE_client_storage and APPLE_texture_range, as described in
+ <https://developer.apple.com/library/mac/documentation/GraphicsImaging/Conceptual/OpenGL-MacProgGuide/opengl_texturedata/opengl_texturedata.html>.
+
+ iOS uses bog-standard glTexImage2D (for now).
+
+ glMapBuffer is the standard way to get data from system RAM to video
+ memory asynchronously and without a memcpy, but support for
+ APPLE_client_storage is ubiquitous on OS X (not so for glMapBuffer),
+ and on iOS GL_PIXEL_UNPACK_BUFFER is only available on OpenGL ES 3
+ (iPhone 5S or newer). Plus, glMapBuffer doesn't work well with
+ CGBitmapContext: glMapBuffer can return a different pointer on each
+ call, but a CGBitmapContext doesn't allow its data pointer to be
+ changed -- and recreating the context for a new pointer can be
+ expensive (glyph caches get dumped, for instance).
+
+ glMapBufferRange has MAP_FLUSH_EXPLICIT_BIT and MAP_UNSYNCHRONIZED_BIT,
+ and these seem to allow mapping the buffer and leaving it where it is
+ in client address space while OpenGL works with the buffer, but it
+ requires OpenGL 3 Core profile on OS X (and ES 3 on iOS for
+ GL_PIXEL_UNPACK_BUFFER), so point goes to APPLE_client_storage.
+
+ AMD_pinned_buffer provides the same advantage as glMapBufferRange, but
+ Apple never implemented that one for OS X.
+ */
+
+ backbuffer_data = NULL;
+ gl_texture_w = (int)new_size.width;
+ gl_texture_h = (int)new_size.height;
+
+ NSAssert (gl_texture_target == GL_TEXTURE_2D
+# ifndef USE_IPHONE
+ || gl_texture_target == GL_TEXTURE_RECTANGLE_EXT
+# endif
+ , @"unexpected GL texture target");
+
+# ifndef USE_IPHONE
+ if (gl_texture_target != GL_TEXTURE_RECTANGLE_EXT)
+# else
+ if (!gl_limited_npot_p)
+# endif
+ {
+ gl_texture_w = to_pow2 (gl_texture_w);
+ gl_texture_h = to_pow2 (gl_texture_h);
+ }
+
+ size_t bytes_per_row = gl_texture_w * 4;
+
+# if defined(BACKBUFFER_OPENGL) && !defined(USE_IPHONE)
+ // APPLE_client_storage requires texture width to be aligned to 32 bytes, or
+ // it will fall back to a memcpy.
+ // https://developer.apple.com/library/mac/documentation/GraphicsImaging/Conceptual/OpenGL-MacProgGuide/opengl_texturedata/opengl_texturedata.html#//apple_ref/doc/uid/TP40001987-CH407-SW24
+ bytes_per_row = (bytes_per_row + 31) & ~31;
+# endif // BACKBUFFER_OPENGL && !USE_IPHONE
+
+ backbuffer_len = bytes_per_row * gl_texture_h;
+ if (backbuffer_len) // mmap requires this to be non-zero.
+ backbuffer_data = mmap (NULL, backbuffer_len,
+ PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED,
+ -1, 0);
+
+ BOOL alpha_first_p, order_little_p;
+
+ if (gl_pixel_format == GL_BGRA) {
+ alpha_first_p = YES;
+ order_little_p = YES;
+/*
+ } else if (gl_pixel_format == GL_ABGR_EXT) {
+ alpha_first_p = NO;
+ order_little_p = YES; */
+ } else {
+ NSAssert (gl_pixel_format == GL_RGBA, @"unknown GL pixel format");
+ alpha_first_p = NO;
+ order_little_p = NO;
+ }
+
+#ifdef USE_IPHONE
+ NSAssert (gl_pixel_type == GL_UNSIGNED_BYTE, @"unknown GL pixel type");
+#else
+ NSAssert (gl_pixel_type == GL_UNSIGNED_INT_8_8_8_8 ||
+ gl_pixel_type == GL_UNSIGNED_INT_8_8_8_8_REV ||
+ gl_pixel_type == GL_UNSIGNED_BYTE,
+ @"unknown GL pixel type");
+
+#if defined __LITTLE_ENDIAN__
+ const GLenum backwards_pixel_type = GL_UNSIGNED_INT_8_8_8_8;
+#elif defined __BIG_ENDIAN__
+ const GLenum backwards_pixel_type = GL_UNSIGNED_INT_8_8_8_8_REV;
+#else
+# error Unknown byte order.
+#endif
+
+ if (gl_pixel_type == backwards_pixel_type)
+ order_little_p ^= YES;
+#endif