feature: Add basic EDID reading, writing, and patching capabilities

edidpatcher/edidpatcher.go

@@ -0,0 +1,102 @@
+package edidpatcher
+
+import (
+	"fmt"
+
+	"github.com/charmbracelet/log"
+	"github.com/google/uuid"
+)
+
+// Calculates a checksum for a given EDID block (base EDID, extension blocks, etc.)
+func CalculateEDIDChecksum(edidBlock []byte) byte {
+	sum := 0
+
+	for _, value := range edidBlock[:len(edidBlock)-1] {
+		sum += int(value)
+	}
+
+	return byte((-sum) & 0xFF)
+}
+
+var MSFTPayloadSize = byte(22 + 4)
+
+// Patch a given EDID to be a "specialized display", allowing for the display to be used by third-party window-managers/compositors/applications directly.
+func PatchEDIDToBeSpecialized(edid []byte) ([]byte, error) {
+	newEDID := make([]byte, len(edid))
+	copy(newEDID, edid)
+
+	isAnEnhancedEDID := len(newEDID) > 128
+
+	foundExtensionBase := 0
+	extensionBaseExists := false
+
+	// Find an appropriate extension base
+	if isAnEnhancedEDID {
+		for currentExtensionPosition := 128; currentExtensionPosition < len(newEDID); currentExtensionPosition += 128 {
+			if newEDID[currentExtensionPosition] != 0x02 {
+				continue
+			}
+
+			if newEDID[currentExtensionPosition+1] != 0x03 {
+				log.Warn("Incompatible version detected for ANSI CTA data section in EDID")
+			}
+
+			foundExtensionBase = currentExtensionPosition
+			extensionBaseExists = true
+		}
+
+		if foundExtensionBase == 0 {
+			foundExtensionBase = len(newEDID)
+			newEDID = append(newEDID, make([]byte, 128)...)
+		}
+	} else {
+		foundExtensionBase = 128
+		newEDID = append(newEDID, make([]byte, 128)...)
+	}
+
+	newEDID[foundExtensionBase+2] = MSFTPayloadSize
+
+	if !extensionBaseExists {
+		// Add another extension to the original EDID
+		if newEDID[126] == 255 {
+			return nil, fmt.Errorf("EDID extension block limit reached, but we need to add another extension")
+		}
+
+		newEDID[126] += 1
+		newEDID[127] = CalculateEDIDChecksum(newEDID[:128])
+
+		newEDID[foundExtensionBase] = 0x02
+		newEDID[foundExtensionBase+1] = 0x03
+		newEDID[foundExtensionBase+3] = 0x00
+	} else {
+		if newEDID[foundExtensionBase+2] != MSFTPayloadSize && newEDID[foundExtensionBase+2] != 0 {
+			currentBase := newEDID[foundExtensionBase+2]
+
+			copy(newEDID[foundExtensionBase+4:foundExtensionBase+int(currentBase)-1], make([]byte, int(currentBase)-1))
+			copy(newEDID[foundExtensionBase+int(MSFTPayloadSize):foundExtensionBase+127], newEDID[foundExtensionBase+int(currentBase):foundExtensionBase+127])
+		}
+	}
+
+	generatedUUID := uuid.New()
+	uuidBytes, err := generatedUUID.MarshalBinary()
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal UUID: %w", err)
+	}
+
+	// Implemented using https://learn.microsoft.com/en-us/windows-hardware/drivers/display/specialized-monitors-edid-extension
+	// VST & Length
+	newEDID[foundExtensionBase+4] = 0x3<<5 | 0x15 // 0x3: vendor specific tag; 0x15: length
+	// Assigned IEEE OUI
+	newEDID[foundExtensionBase+5] = 0x5C
+	newEDID[foundExtensionBase+6] = 0x12
+	newEDID[foundExtensionBase+7] = 0xCA
+	// Actual data
+	newEDID[foundExtensionBase+8] = 0x2 // Using version 0x2 for better compatibility
+	newEDID[foundExtensionBase+9] = 0x7 // Using VR tag for better compatibility even though it probably doesn't matter
+	copy(newEDID[foundExtensionBase+10:foundExtensionBase+10+16], uuidBytes)
+
+	newEDID[foundExtensionBase+127] = CalculateEDIDChecksum(newEDID[foundExtensionBase : foundExtensionBase+127])
+
+	return newEDID, nil
+}