GL_EXT_packed_pixels vs GL_APPLE_packed_pixels - macos

Question

My application checks for GL_EXT_packed_pixels extension before using packed pixel formats such as UNSIGNED_INT_8_8_8_8_EXT. On my MacBook, my code can't find this extension, despite that using packed pixel formats still appears to work.
OpenGL Extension Viewer seems to suggest that it has a special name on OS X:
What's the difference? Should I just check for either GL_EXT_packed_pixels or GL_APPLE_packed_pixels when assessing if UNSIGNED_INT_8_8_8_8_EXT is supported?

Answer 1

EXT_packed_pixels has these definitions:
UNSIGNED_BYTE_3_3_2_EXT 0x8032
UNSIGNED_SHORT_4_4_4_4_EXT 0x8033
UNSIGNED_SHORT_5_5_5_1_EXT 0x8034
UNSIGNED_INT_8_8_8_8_EXT 0x8035
UNSIGNED_INT_10_10_10_2_EXT 0x8036
While APPLE_packed_pixels has these:
UNSIGNED_BYTE_3_3_2 0x8032
UNSIGNED_BYTE_2_3_3_REV 0x8362
UNSIGNED_SHORT_5_6_5 0x8363
UNSIGNED_SHORT_5_6_5_REV 0x8364
UNSIGNED_SHORT_4_4_4_4 0x8033
UNSIGNED_SHORT_4_4_4_4_REV 0x8365
UNSIGNED_SHORT_5_5_5_1 0x8034
UNSIGNED_SHORT_1_5_5_5_REV 0x8366
UNSIGNED_INT_8_8_8_8 0x8035
UNSIGNED_INT_8_8_8_8_REV 0x8367
UNSIGNED_INT_10_10_10_2 0x8036
UNSIGNED_INT_2_10_10_10_REV 0x8368
Comparing the two, EXT_packed_pixels is a subset of APPLE_packed_pixels, and the shared values are the same. Therefore, if APPLE_packed_pixels is supported, you can safely use all definitions from EXT_packed_pixels.
As your screen shot of the extension viewer already suggests, GL_EXT_packed_pixels has been core functionality since OpenGL 1.2. So in most cases, you should not have to test for any of these in the extension string. If you check the version first, and it's at least 1.2, you already know that the functionality is available. The test logic could look like this:
if (strcmp(glGetString(GL_VERSION), "1.2") >= 0 ||
strstr(glGetString(GL_EXTENSIONS), "_packed_pixels") != NULL)
{
// supported
}