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POHow to resolve CGDirectDisplayID changing issues on newer multi-GPU Apple laptops in Core Foundation/IO Kit?
 

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  1. POHow to resolve CGDirectDisplayID changing issues on newer multi-GPU Apple laptops in Core Foundation/IO Kit?
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    <p>In Mac OS X, every display gets a unique <code>CGDirectDisplayID</code> number assigned to it. You can use <code>CGGetActiveDisplayList(</code>) or <code>[NSScreen screens]</code> to access them, among others. Per <a href="http://CGDisplayRegisterReconfigurationCallback" rel="noreferrer">Apple's docs</a>:</p> <blockquote> <p>A display ID can persist across processes and system reboot, and typically remains constant as long as certain display parameters do not change.</p> </blockquote> <p>On newer mid-2010 MacBook Pro's, Apple started using auto-switching Intel/nVidia graphics. Laptops have two GPU's, a low-powered Intel, and a high-powered nVidia. Previous dual-GPU laptops (2009 models) didn't have auto-GPU switching, and required the user to make a settings change, logoff, and then logon again to make a GPU switch occur. Even older systems only had one GPU.</p> <p>There's an issue with the mid-2010 models where CGDirectDisplayID's don't remain the same when a display switches from one GPU to the next. For example:</p> <ol> <li>Laptop powers on.</li> <li>Built-In <strong>LCD Screen</strong> is driven by Intel chipset. Display ID: <strong>30002</strong></li> <li><strong>External Display</strong> is plugged in.</li> <li>Built-In <strong>LCD Screen</strong> switches to nVidia chipset. It's display ID changes: <strong>30004</strong></li> <li><strong>External Display</strong> is driven by nVidia chipset.</li> <li>...at this point, the Intel chipset is dormant...</li> <li>User unplugs <strong>External Display</strong>.</li> <li>Built-In <strong>LCD Screen</strong> switches back to Intel chipset. It's display ID changes back to original: <strong>30002</strong></li> </ol> <p><strong>My question is, how can I match an old display ID to a new display ID when they alter due to a GPU change?</strong></p> <hr> <p><strong>Thought about:</strong></p> <p>I've noticed that the display ID only changes by 2, but I don't have enough test Mac's available to determine if this is common to all new MacBook Pro's, or just mine. Kind of a kludge if "just check for display ID's which are +/-2 from one another" works, anyway.</p> <hr> <p><strong>Tried:</strong></p> <p><code>CGDisplayRegisterReconfigurationCallback()</code>, which notifies before-and-after when displays are going to change, has no matching logic. Putting something like this inside a method registered with it doesn't work:</p> <pre><code>// Run before display settings change: CGDirectDisplayID directDisplayID = ...; io_service_t servicePort = CGDisplayIOServicePort(directDisplayID); CFDictionaryRef oldInfoDict = IODisplayCreateInfoDictionary(servicePort, kIODisplayMatchingInfo); // ...display settings change... // Run after display settings change: CGDirectDisplayID directDisplayID = ...; io_service_t servicePort = CGDisplayIOServicePort(directDisplayID); CFDictionaryRef newInfoDict = IODisplayCreateInfoDictionary(servicePort, kIODisplayMatchingInfo); BOOL match = IODisplayMatchDictionaries(oldInfoDict, newInfoDict, 0); if (match) NSLog(@"Displays are a match"); else NSLog(@"Displays are not a match"); </code></pre> <p>What's happening above is:</p> <ol> <li>I'm caching <strong>oldInfoDict</strong> before display settings change.</li> <li>Waiting for display settings to change</li> <li>Then comparing <strong>oldInfoDict</strong> to <strong>newInfoDict</strong> by using <code>IODisplayMatchDictionaries()</code></li> <li><code>IODisplayMatchDictionaries()</code> returns a BOOL, either YES they're the same, or NO they're different.</li> </ol> <p>Unfortunately, <code>IODisplayMatchDictionaries()</code> doesn't return YES if the same display changed GPU's. Here's an example of the dictionary's it's comparing (look at the <code>IODisplayLocation</code> key):</p> <pre><code>// oldInfoDict (Display ID: 30002) oldInfoDict: { DisplayProductID = 40144; DisplayVendorID = 1552; IODisplayLocation = "IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/IGPU@2/AppleIntelFramebuffer/display0/AppleBacklightDisplay"; } // newInfoDict (Display ID: 30004) newInfoDict: { DisplayProductID = 40144; DisplayVendorID = 1552; IODisplayLocation = "IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/P0P2@1/IOPCI2PCIBridge/GFX0@0/NVDA,Display-A@0/NVDA/display0/AppleBacklightDisplay"; } </code></pre> <p>As you can see, the <code>IODisplayLocation</code> key changes when GPU's are switched, hence <code>IODisplayMatchDictionaries()</code> doesn't work.</p> <p>I can, theoretically, compared just the <code>DisplayProductID</code> and <code>DisplayVendorID</code> keys, but I'm writing end-user software, and am worried of a situation where users have two or more identical monitors plugged in (meaning they'll both have the same DisplayProductID/DisplayVendorID). In other words, it's a less-than-perfect solution open to potential glitches.</p> <hr> <p>Any help is greatly appreciated! :)</p>
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