Checks the possibility of overscans from EDID extension data.

ui/base/x/x11_util.cc

Index: ui/base/x/x11_util.cc
diff --git a/ui/base/x/x11_util.cc b/ui/base/x/x11_util.cc
index 539c87910e3debd24cf29925efad308cd124d7e6..eb8811b7b0082a8fff33332b8c9f48599b2482fd 100644
--- a/ui/base/x/x11_util.cc
+++ b/ui/base/x/x11_util.cc
@@ -331,6 +331,48 @@ bool IsShapeAvailable() {
 
 }
 
+bool GetEDIDProperty(XID output, unsigned long* nitems, unsigned char* prop) {

[Daniel Erat, 2013/01/03 19:04:19]

nit: add a comment stating that the caller must free |prop| using XFree()

[Jun Mukai, 2013/01/03 21:37:37]

Done.

+  if (!IsRandRAvailable())
+    return false;
+
+  static Atom edid_property = GetAtom(RR_PROPERTY_RANDR_EDID);
+
+  Display* display = GetXDisplay();
+
+  bool has_edid_property = false;
+  int num_properties = 0;
+  Atom* properties = XRRListOutputProperties(display, output, &num_properties);
+  for (int i = 0; i < num_properties; ++i) {
+    if (properties[i] == edid_property) {
+      has_edid_property = true;
+      break;
+    }
+  }
+  XFree(properties);
+  if (!has_edid_property)
+    return false;
+
+  Atom actual_type;
+  int actual_format;
+  unsigned long bytes_after;
+  XRRGetOutputProperty(display,
+                       output,
+                       edid_property,
+                       0,                // offset
+                       128,              // length
+                       false,            // _delete
+                       false,            // pending
+                       AnyPropertyType,  // req_type
+                       &actual_type,
+                       &actual_format,
+                       nitems,
+                       &bytes_after,
+                       &prop);
+  DCHECK_EQ(XA_INTEGER, actual_type);
+  DCHECK_EQ(8, actual_format);
+  return true;
+}
+
 }  // namespace
 
 bool XDisplayExists() {
@@ -1248,47 +1290,11 @@ bool GetOutputDeviceData(XID output,
                          uint16* manufacturer_id,
                          uint32* serial_number,
                          std::string* human_readable_name) {
-  if (!IsRandRAvailable())
-    return false;
-
-  static Atom edid_property = GetAtom(RR_PROPERTY_RANDR_EDID);
-
-  Display* display = GetXDisplay();
-
-  bool has_edid_property = false;
-  int num_properties = 0;
-  Atom* properties = XRRListOutputProperties(display, output, &num_properties);
-  for (int i = 0; i < num_properties; ++i) {
-    if (properties[i] == edid_property) {
-      has_edid_property = true;
-      break;
-    }
-  }
-  XFree(properties);
-  if (!has_edid_property)
+  unsigned long nitems = 0;
+  unsigned char *prop = NULL;
+  if (!GetEDIDProperty(output, &nitems, prop))

[sadrul, 2013/01/03 19:08:32]

This doesn't actually set the value of |prop|, does it? Shouldn't you need to
send &prop?

[Jun Mukai, 2013/01/03 21:37:37]

aww, right. Fixed.

     return false;
 
-  Atom actual_type;
-  int actual_format;
-  unsigned long nitems;
-  unsigned long bytes_after;
-  unsigned char *prop;
-  XRRGetOutputProperty(display,
-                       output,
-                       edid_property,
-                       0,                // offset
-                       128,              // length
-                       false,            // _delete
-                       false,            // pending
-                       AnyPropertyType,  // req_type
-                       &actual_type,
-                       &actual_format,
-                       &nitems,
-                       &bytes_after,
-                       &prop);
-  DCHECK_EQ(XA_INTEGER, actual_type);
-  DCHECK_EQ(8, actual_format);
-
   // See http://en.wikipedia.org/wiki/Extended_display_identification_data
   // for the details of EDID data format.  We use the following data:
   //   bytes 8-9: manufacturer EISA ID, in big-endian
@@ -1372,6 +1378,85 @@ bool GetOutputDeviceData(XID output,
   return true;
 }
 
+bool GetOutputOverscanFlag(XID output) {

[Daniel Erat, 2013/01/03 19:04:19]

since this code does a lot of tricky byte-reading, it would be better to move
most of it into a separate ParseEDIDProperty() function and write unit tests for
it.

[Jun Mukai, 2013/01/03 21:37:37]

Added.

+  unsigned long nitems = 0;
+  unsigned char *prop = NULL;
+  if (!GetEDIDProperty(output, &nitems, prop))
+    return false;
+
+  const unsigned int kNumExtensionsOffset = 126;
+  if (nitems < kNumExtensionsOffset) {
+    XFree(prop);
+    return false;
+  }
+
+  // See http://en.wikipedia.org/wiki/Extended_display_identification_data
+  // for the extension format of EDID.  Also see
+  // http://blogimg.chinaunix.net/blog/upfile2/090903185737.pdf pg.87-
+  // for the format of the extensions and how video capability is encoded.
+  //  - byte 0: tag.  should be 02h.
+  //  - byte 1: revision.  only cares revision 3 (03h).
+  //  - byte 4-: data block.
+  const unsigned int kExtensionBase = 128;
+  const unsigned int kExtensionSize = 128;
+  const unsigned int kDataBlockOffset = 4;
+  const unsigned char kCEAExtensionTag = '\x02';
+  const unsigned char kExpectedExtensionRevision = '\x03';
+  const unsigned char kExtendedTag = 7;
+  const unsigned char kExtendedVideoCapabilityTag = 0;
+  const unsigned int kPTOverscan = 4;
+  const unsigned int kITOverscan = 2;
+  const unsigned int kCEOverscan = 0;
+
+  unsigned char num_extensions = prop[kNumExtensionsOffset];
+  bool result = false;
+  bool found = false;
+
+  for (size_t i = 0; i < num_extensions && !found; ++i) {
+    unsigned char* extension = prop + kExtensionBase + i * kExtensionSize;
+    unsigned char tag = extension[0];
+    unsigned char revision = extension[1];
+    if (tag != kCEAExtensionTag || revision != kExpectedExtensionRevision)
+      continue;
+
+    unsigned char timing_descriptors_start = extension[2];
+    unsigned char* data_block = extension + kDataBlockOffset;
+    while (data_block < extension + timing_descriptors_start) {
+      // a data block is encoded as:
+      // - byte 1 high 3 bits: tag. '07' for extended tags.
+      // - byte 1 remaining bits: the length of data block.
+      // - byte 2: the extended tag.  '0' for video capability.
+      // - byte 3: the capability.
+      unsigned char tag = data_block[0] >> 5;
+      unsigned char payload_length = data_block[0] & 0x1f;
+      if (tag != kExtendedTag && payload_length < 2) {
+        data_block += payload_length + 1;
+        continue;
+      }
+
+      unsigned char extended_tag_code = data_block[1];
+      // Here doesn't care the difference between preferred video format /

[Daniel Erat, 2013/01/03 19:04:19]

nit: reword this to something like:

// The difference between preferred, IT, and CE video formats
// doesn't matter since this tag is skipped.

[Jun Mukai, 2013/01/03 21:37:37]

Sorry, the comment location was wrong. Moved to the right position (below) and
rephrased as you suggested.

+      // IT video format / CE video format, since it just checks the
+      // possibility.
+      if (extended_tag_code != kExtendedVideoCapabilityTag) {
+        data_block += payload_length;
+        continue;
+      }
+
+      found = true;
+      if ((data_block[2] & (1 << kPTOverscan)) ||
+          (data_block[2] & (1 << kITOverscan)) ||
+          (data_block[2] & (1 << kCEOverscan))) {
+        result = true;
+      }
+      break;
+    }
+  }
+
+  XFree(prop);
+  return result;
+}
+
 std::vector<std::string> GetDisplayNames(const std::vector<XID>& output_ids) {
   std::vector<std::string> names;
   for (size_t i = 0; i < output_ids.size(); ++i) {