Monitor (macOS): test HDR support for external monitors

Author: CarterLi

src/detection/monitor/monitor_apple.m

@@ -106,11 +106,13 @@
         if (IOAVServiceCopyEDID(service, &edid) != KERN_SUCCESS)
             continue;
 
-        if (CFDataGetLength(edid) < 128)
+        uint32_t edidLength = (uint32_t) CFDataGetLength(edid);
+        if (edidLength == 0 || edidLength % 128 != 0)
             continue;
 
         uint32_t width, height;
         const uint8_t* edidData = CFDataGetBytePtr(edid);
+
         ffEdidGetPhysicalResolution(edidData, &width, &height);
         if (width == 0 || height == 0) continue;
 
@@ -120,7 +122,7 @@
         ffStrbufInit(&display->name);
         ffEdidGetName(edidData, &display->name);
         ffEdidGetPhysicalSize(edidData, &display->physicalWidth, &display->physicalHeight);
-        display->hdrCompatible = false;
+        display->hdrCompatible = ffEdidGetHdrCompatible(edidData, edidLength);
     }
     return NULL;
 }

src/util/edidHelper.c

@@ -49,3 +49,32 @@ void ffEdidGetPhysicalSize(const uint8_t edid[128], uint32_t* width, uint32_t* h
     *width = (((uint32_t) edid[68] & 0xF0) << 4) + edid[66];
     *height = (((uint32_t) edid[68] & 0x0F) << 8) + edid[67];
 }
+
+bool ffEdidGetHdrCompatible(const uint8_t* edid, uint32_t length)
+{
+    if (length <= 128) return false;
+    for (const uint8_t* cta = &edid[128]; cta < &edid[length]; cta += 128)
+    {
+        // https://en.wikipedia.org/wiki/Extended_Display_Identification_Data#CTA_EDID_Timing_Extension_Block
+        if (cta[0] != 0x02 /* CTA EDID */) continue;
+        if (cta[1] < 0x03 /* Version 3 */) continue;
+        const uint8_t offset = cta[2];
+        if (offset <= 4) continue;
+        for (uint8_t i = 4; i < offset;)
+        {
+            uint8_t blkLen = cta[i] & 0x1f;
+            if (blkLen > 0)
+            {
+                uint8_t blkTag = (cta[i] & 0xe0) >> 5;
+                if (blkTag == 0x07 /* Extended Block Type Tag */)
+                {
+                    uint8_t extendedTag = cta[i + 1];
+                    if (extendedTag == 6 /* HDR SMDB */ || extendedTag == 7 /* HDR DMDB */)
+                        return true;
+                }
+            }
+            i += blkLen + 1;
+        }
+    }
+    return false;
+}

src/util/edidHelper.h

@@ -10,5 +10,6 @@ void ffEdidGetVendorAndModel(const uint8_t edid[128], FFstrbuf* result);
 bool ffEdidGetName(const uint8_t edid[128], FFstrbuf* name);
 void ffEdidGetPhysicalResolution(const uint8_t edid[128], uint32_t* width, uint32_t* height);
 void ffEdidGetPhysicalSize(const uint8_t edid[128], uint32_t* width, uint32_t* height); // in mm
+bool ffEdidGetHdrCompatible(const uint8_t edid[128], uint32_t length);
 
 #endif