Update help in SkFlags.

tools/SkFlags.cpp

Index: tools/SkFlags.cpp
diff --git a/tools/SkFlags.cpp b/tools/SkFlags.cpp
index e386b429fe5ca5dd5e2bb6e38d9401a3c841d6f2..84b5ef297dd73e914b4796668819ee3958b082bd 100644
--- a/tools/SkFlags.cpp
+++ b/tools/SkFlags.cpp
@@ -17,6 +17,56 @@ void SkFlags::SetUsage(const char* usage) {
 // Maximum line length for the help message.
 #define LINE_LENGTH 80
 
+static void print_help_for_flag(const SkFlagInfo* flag) {
+    SkDebugf("\t--%s", flag->name().c_str());
+    const SkString& shortName = flag->shortName();
+    if (shortName.size() > 0) {
+        SkDebugf(" or -%s", shortName.c_str());
+    }
+    SkDebugf(":\ttype: %s", flag->typeAsString().c_str());
+    if (flag->defaultValue().size() > 0) {
+        SkDebugf("\tdefault: %s", flag->defaultValue().c_str());
+    }
+    SkDebugf("\n");
+    const SkString& help = flag->help();
+    size_t length = help.size();
+    const char* currLine = help.c_str();
+    const char* stop = currLine + length;
+    while (currLine < stop) {
+        if (strlen(currLine) < LINE_LENGTH) {
+            // Only one line length's worth of text left.
+            SkDebugf("\t\t%s\n", currLine);
+            break;
+        }
+        int lineBreak = SkStrFind(currLine, "\n");
+        if (lineBreak < 0 || lineBreak > LINE_LENGTH) {
+            // No line break within line length. Will need to insert one.
+            // Find a space before the line break.
+            int spaceIndex = LINE_LENGTH - 1;
+            while (spaceIndex > 0 && currLine[spaceIndex] != ' ') {
+                spaceIndex--;
+            }
+            int gap;
+            if (0 == spaceIndex) {
+                // No spaces on the entire line. Go ahead and break mid word.
+                spaceIndex = LINE_LENGTH;
+                gap = 0;
+            } else {
+                // Skip the space on the next line
+                gap = 1;
+            }
+            SkDebugf("\t\t%.*s\n", spaceIndex, currLine);
+            currLine += spaceIndex + gap;
+        } else {
+            // the line break is within the limit. Break there.
+            lineBreak++;
+            SkDebugf("\t\t%.*s", lineBreak, currLine);
+            currLine += lineBreak;
+        }
+    }
+    SkDebugf("\n");
+}
+
 void SkFlags::ParseCommandLine(int argc, char** argv) {
     // Only allow calling this function once.
     static bool gOnce;
@@ -34,55 +84,43 @@ void SkFlags::ParseCommandLine(int argc, char** argv) {
         if (0 == strcmp("-h", argv[i]) || 0 == strcmp("--h", argv[i])
                 || 0 == strcmp("-help", argv[i]) || 0 == strcmp("--help", argv[i])) {
             // Print help message.
-            SkDebugf("%s\n%s\n", argv[0], gUsage.c_str());
+            SkTDArray<const char*> helpFlags;
+            for (int j = i + 1; j < argc; j++) {
+                if (SkStrStartsWith(argv[j], '-')) {
+                    break;
+                }
+                helpFlags.append(1, &argv[j]);
+            }
+            if (0 == helpFlags.count()) {
+                // Only print general help message if help for specific flags is not requested.
+                SkDebugf("%s\n%s\n", argv[0], gUsage.c_str());
+            }
             SkDebugf("Flags:\n");
             SkFlagInfo* flag = SkFlags::gHead;
             while (flag != NULL) {
-                SkDebugf("\t--%s:\ttype: %s", flag->name().c_str(),
-                          flag->typeAsString().c_str());
-                if (flag->defaultValue().size() > 0) {
-                    SkDebugf("\tdefault: %s", flag->defaultValue().c_str());
-                }
-                SkDebugf("\n");
-                const SkString& help = flag->help();
-                size_t length = help.size();
-                const char* currLine = help.c_str();
-                const char* stop = currLine + length;
-                while (currLine < stop) {
-                    if (strlen(currLine) < LINE_LENGTH) {
-                        // Only one line length's worth of text left.
-                        SkDebugf("\t\t%s\n", currLine);
-                        break;
-                    }
-                    int lineBreak = SkStrFind(currLine, "\n");
-                    if (lineBreak < 0 || lineBreak > LINE_LENGTH) {
-                        // No line break within line length. Will need to insert one.
-                        // Find a space before the line break.
-                        int spaceIndex = LINE_LENGTH - 1;
-                        while (spaceIndex > 0 && currLine[spaceIndex] != ' ') {
-                            spaceIndex--;
-                        }
-                        int gap;
-                        if (0 == spaceIndex) {
-                            // No spaces on the entire line. Go ahead and break mid word.
-                            spaceIndex = LINE_LENGTH;
-                            gap = 0;
-                        } else {
-                            // Skip the space on the next line
-                            gap = 1;
+                // If no flags followed --help, print them all
+                bool printFlag = 0 == helpFlags.count();
+                if (!printFlag) {
+                    for (int k = 0; k < helpFlags.count(); k++) {
+                        if (flag->name().equals(helpFlags[k]) ||
+                            flag->shortName().equals(helpFlags[k])) {
+                            printFlag = true;
+                            helpFlags.remove(k);
+                            break;
                         }
-                        SkDebugf("\t\t%.*s\n", spaceIndex, currLine);
-                        currLine += spaceIndex + gap;
-                    } else {
-                        // the line break is within the limit. Break there.
-                        lineBreak++;
-                        SkDebugf("\t\t%.*s", lineBreak, currLine);
-                        currLine += lineBreak;
                     }
                 }
-                SkDebugf("\n");
+                if (printFlag) {
+                    print_help_for_flag(flag);
+                }
                 flag = flag->next();
             }
+            if (helpFlags.count() > 0) {
+                SkDebugf("Requested help for unrecognized flags:\n");
+                for (int k = 0; k < helpFlags.count(); k++) {
+                    SkDebugf("\t--%s\n", helpFlags[k]);
+                }
+            }
             helpPrinted = true;
         }
         if (!helpPrinted) {