add a simple ascii-art debug thing for AA clips

BUG=skia:
R=reed@google.com

Author: humper@google.com

Review URL: https://codereview.chromium.org/450423002

src/core/SkAAClip.cpp

@@ -219,6 +219,46 @@ void SkAAClip::validate() const {
     --yoff;
     SkASSERT(yoff->fY == lastY);
 }
+
+static void dump_one_row(const uint8_t* SK_RESTRICT row,
+                         int width, int leading_num) {
+    if (leading_num) {
+        SkDebugf( "%03d ", leading_num );
+    }
+    while (width > 0) {
+        int n = row[0];
+        int val = row[1];
+        char out = '.';
+        if (val == 0xff) {
+            out = '*';
+        } else if (val > 0) {
+            out = '+';
+        }
+        for (int i = 0 ; i < n ; i++) {
+            SkDebugf( "%c", out );
+        }
+        row += 2;
+        width -= n;
+    }
+    SkDebugf( "\n" );
+}
+
+void SkAAClip::debug(bool compress_y) const {
+    Iter iter(*this);
+    const int width = fBounds.width();
+
+    int y = fBounds.fTop;
+    while (!iter.done()) {
+        if (compress_y) {
+            dump_one_row(iter.data(), width, iter.bottom() - iter.top() + 1);
+        } else {
+            do {
+                dump_one_row(iter.data(), width, 0);
+            } while (++y < iter.bottom());
+        }
+        iter.next();
+    }
+}
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////

src/core/SkAAClip.h

@@ -75,8 +75,10 @@ public:
 
 #ifdef SK_DEBUG
     void validate() const;
+    void debug(bool compress_y=false) const;
 #else
     void validate() const {}
+    void debug(bool compress_y=false) const {}
 #endif
 
 private: