This PR adds **Core** iOS support to the OpenUSD project. This does not include Imaging, and any Imaging related components at this time. Imaging will be added in a follow up PR.

It is a minimal version of PixarAnimationStudios#2455 against the latest `dev` branch.
Changes include:
* Using latest dev branch
* No imaging support. Will be added in a follow up PR.
* Makes use of CMake's inbuilt iOS support, negating the need for toolchain support
* Structures the code in such a way that we can add support for other iOS derived platforms+simulator in future PRs
* Swaps `ARCH_OS_IOS` with `ARCH_OS_IPHONE` to align with compiler directives. IPHONE refers to all derivative platforms, whereas iOS refers to only iPhone/iPad (Confusing but the case for historical reasons as [documented here](https://chaosinmotion.com/2021/08/02/things-to-remember-compiler-conditionals-for-macos-ios-etc/))
* Upgrades MaterialX to 1.38.8 (from 1.38.7) as that adds support for iOS derivative platforms as well.

This PR requires PixarAnimationStudios#2947 to be merged first as that allows for not requiring Boost patches per platform, which can get fragile.

Author: dgovil

README.md

@@ -129,7 +129,7 @@ then build and install USD into `/path/to/my_usd_install_dir`.
 > python USD/build_scripts/build_usd.py /path/to/my_usd_install_dir
 ```
 
-##### MacOS:
+##### macOS:
 
 In a terminal, run `xcode-select` to ensure command line developer tools are
 installed. Then run the script.
@@ -141,6 +141,14 @@ then build and install USD into `/path/to/my_usd_install_dir`.
 > python USD/build_scripts/build_usd.py /path/to/my_usd_install_dir
 ```
 
+###### iOS
+
+When building from a macOS system, you can also cross compile for other iOS.
+To build for iOS, add the `--build-target iOS` parameter.
+
+iOS builds currently do not support Imaging.
+Additionally, they will not support Python bindings or command line tools.
+
 ##### Windows:
 
 Launch the "x64 Native Tools Command Prompt" for your version of Visual Studio

build_scripts/apple_utils.py

@@ -35,44 +35,46 @@
 import platform
 import shlex
 import subprocess
+import re
+from typing import Optional, List
 
 TARGET_NATIVE = "native"
 TARGET_X86 = "x86_64"
 TARGET_ARM64 = "arm64"
 TARGET_UNIVERSAL = "universal"
+TARGET_IOS = "ios"
+
+EMBEDDED_PLATFORMS = [TARGET_IOS]
 
 def GetBuildTargets():
     return [TARGET_NATIVE,
             TARGET_X86,
             TARGET_ARM64,
-            TARGET_UNIVERSAL]
+            TARGET_UNIVERSAL,
+            TARGET_IOS]
 
 def GetBuildTargetDefault():
-    return TARGET_NATIVE;
+    return TARGET_NATIVE
 
 def MacOS():
     return platform.system() == "Darwin"
 
 def GetLocale():
     return sys.stdout.encoding or locale.getdefaultlocale()[1] or "UTF-8"
 
-def GetCommandOutput(command):
-    """Executes the specified command and returns output or None."""
+def GetCommandOutput(command, **kwargs):
     try:
-        return subprocess.check_output(
-            shlex.split(command),
-            stderr=subprocess.STDOUT).decode(GetLocale(), 'replace').strip()
-    except subprocess.CalledProcessError:
-        pass
-    return None
+        return subprocess.check_output(command, stderr=subprocess.STDOUT, **kwargs).decode(GetLocale(), 'replace').strip()
+    except:
+        return None
 
 def GetTargetArmArch():
     # Allows the arm architecture string to be overridden by
     # setting MACOS_ARM_ARCHITECTURE
     return os.environ.get('MACOS_ARM_ARCHITECTURE') or TARGET_ARM64
 
 def GetHostArch():
-    macArch = GetCommandOutput('arch').strip()
+    macArch = GetCommandOutput(["arch"])
     if macArch == "i386" or macArch == TARGET_X86:
         macArch = TARGET_X86
     else:
@@ -85,7 +87,7 @@ def GetTargetArch(context):
     else:
         if context.targetX86:
             macTargets = TARGET_X86
-        if context.targetARM64:
+        if context.targetARM64 or context.targetIos:
             macTargets = GetTargetArmArch()
         if context.targetUniversal:
             macTargets = TARGET_X86 + ";" + GetTargetArmArch()
@@ -106,6 +108,8 @@ def GetTargetArchPair(context):
         primaryArch = TARGET_X86
     if context.targetARM64:
         primaryArch = GetTargetArmArch()
+    if context.targetIos:
+        primaryArch = TARGET_IOS
     if context.targetUniversal:
         primaryArch = GetHostArch()
         if (primaryArch == TARGET_X86):
@@ -118,18 +122,52 @@ def GetTargetArchPair(context):
 def SupportsMacOSUniversalBinaries():
     if not MacOS():
         return False
-    XcodeOutput = GetCommandOutput('/usr/bin/xcodebuild -version')
+    XcodeOutput = GetCommandOutput(["/usr/bin/xcodebuild", "-version"])
     XcodeFind = XcodeOutput.rfind('Xcode ', 0, len(XcodeOutput))
     XcodeVersion = XcodeOutput[XcodeFind:].split(' ')[1]
     return (XcodeVersion > '11.0')
 
+
+def GetSDKVersion(sdk: str) -> Optional[str]:
+    """Gets the SDK version from the currently active Xcode"""
+    sdks = GetCommandOutput(["xcodebuild", "-showsdks"]).split(os.linesep)
+    for line in sdks:
+        line = line.strip()
+        if sdk not in line or "-sdk" not in line:
+            continue
+
+        line = line.split("-sdk ")[-1]
+        if not line.startswith(sdk):
+            continue
+
+        tokens = [t for t in line.replace(sdk, "").split(".") if t.isnumeric()]
+        if not tokens:
+            continue
+        return ".".join(tokens)
+    return None
+
+def GetSDKRoot(context) -> Optional[str]:
+    sdk = "macosx"
+    if context.buildTarget == TARGET_IOS:
+        sdk = "iphoneos"
+
+    for arg in (context.cmakeBuildArgs or '').split():
+        if "CMAKE_OSX_SYSROOT" in arg:
+            override = arg.split('=')[1].strip('"').strip()
+            if override:
+                sdk = override
+    return GetCommandOutput(["xcrun", "--sdk", sdk, "--show-sdk-path"])
+
+
 def SetTarget(context, targetName):
     context.targetNative = (targetName == TARGET_NATIVE)
     context.targetX86 = (targetName == TARGET_X86)
     context.targetARM64 = (targetName == GetTargetArmArch())
     context.targetUniversal = (targetName == TARGET_UNIVERSAL)
+    context.targetIos = (targetName == TARGET_IOS)
+    context.iosVersion = GetSDKVersion("iphoneos") if context.targetIos else None
     if context.targetUniversal and not SupportsMacOSUniversalBinaries():
-        self.targetUniversal = False
+        context.targetUniversal = False
         raise ValueError(
                 "Universal binaries only supported in macOS 11.0 and later.")
 
@@ -150,26 +188,63 @@ def ExtractFilesRecursive(path, cond):
                 files.append(os.path.join(r, file))
     return files
 
-def CodesignFiles(files):
-    SDKVersion  = subprocess.check_output(
-        ['xcodebuild', '-version']).strip()[6:10]
-    codeSignIDs = subprocess.check_output(
-        ['security', 'find-identity', '-vp', 'codesigning'])
+def _GetCodeSignStringFromTerminal():
+    codeSignIDs = GetCommandOutput(['security', 'find-identity', '-vp', 'codesigning'])
+    return codeSignIDs
 
-    codeSignID = "-"
+def GetCodeSignID():
     if os.environ.get('CODE_SIGN_ID'):
-        codeSignID = os.environ.get('CODE_SIGN_ID')
-    elif float(SDKVersion) >= 11.0 and \
-                codeSignIDs.find(b'Apple Development') != -1:
-        codeSignID = "Apple Development"
-    elif codeSignIDs.find(b'Mac Developer') != -1:
-        codeSignID = "Mac Developer"
+        return os.environ.get('CODE_SIGN_ID')
+
+    codeSignIDs = _GetCodeSignStringFromTerminal()
+    if not codeSignIDs:
+        return "-"
+    for codeSignID in codeSignIDs.splitlines():
+        if "CSSMERR_TP_CERT_REVOKED" in codeSignID:
+            continue
+        if ")" not in codeSignID:
+            continue
+        codeSignID = codeSignID.split()[1]
+        break
+    else:
+        raise RuntimeError("Could not find a valid codesigning ID")
+
+    return codeSignID or "-"
+
+def GetCodeSignIDHash():
+    codeSignIDs = _GetCodeSignStringFromTerminal()
+    try:
+        return re.findall(r'\(.*?\)', codeSignIDs)[0][1:-1]
+    except:
+        raise Exception("Unable to parse codesign ID hash")
+
+def GetDevelopmentTeamID():
+    if os.environ.get("DEVELOPMENT_TEAM"):
+        return os.environ.get("DEVELOPMENT_TEAM")
+    codesignID = GetCodeSignIDHash()
+
+    certs = subprocess.check_output(["security", "find-certificate", "-c", codesignID, "-p"])
+    subject = GetCommandOutput(["openssl", "x509", "-subject"], input=certs)
+    subject = subject.splitlines()[0]
+
+    # Extract the Organizational Unit (OU field) from the cert
+    try:
+        team = [elm for elm in subject.split(
+            '/') if elm.startswith('OU')][0].split('=')[1]
+        if team is not None and team != "":
+            return team
+    except Exception as ex:
+        raise Exception("No development team found with exception " + ex)
+
+def CodesignFiles(files):
+    codeSignID = GetCodeSignID()
 
     for f in files:
         subprocess.call(['codesign', '-f', '-s', '{codesignid}'
-                              .format(codesignid=codeSignID), f],
+                        .format(codesignid=codeSignID), f],
                         stdout=devout, stderr=devout)
 
+
 def Codesign(install_path, verbose_output=False):
     if not MacOS():
         return False
@@ -217,3 +292,12 @@ def CreateUniversalBinaries(context, libNames, x86Dir, armDir):
                                 instDir=context.instDir, libName=targetName),
                        outputName)
     return lipoCommands
+
+def ConfigureCMakeExtraArgs(context, args:List[str]) -> List[str]:
+    system_name = None
+    if context.buildTarget == TARGET_IOS:
+        system_name = "iOS"
+
+    if system_name:
+        args.append(f"-DCMAKE_SYSTEM_NAME={system_name}")
+    return args