Correctly compute the number of bytes written by each op.

Bug #6157792

Previously, DisplayListRenderer would compute the number of bytes
written after a drawing op by looking at the difference between
the start pointer of the command stream and the end pointer of
the command stream. The SkWriter class used to record the commands
stream allocates blocks of storage which would cause a crash when
a command spanned two blocks.

Change-Id: I4d79d3feeb6d72d9d4e6ab05ecebd72d004be56c

Author: Romain Guy

libs/hwui/DisplayListRenderer.cpp

@@ -826,7 +826,7 @@ bool DisplayList::replay(OpenGLRenderer& renderer, uint32_t width,
     while (!mReader.eof()) {
         int op = mReader.readInt();
         if (op & OP_MAY_BE_SKIPPED_MASK) {
-            int32_t skip = mReader.readInt() * 4;
+            int32_t skip = mReader.readInt();
             if (CC_LIKELY(flags & kReplayFlag_ClipChildren)) {
                 mReader.skip(skip);
                 DISPLAY_LIST_LOGD("%s%s skipping %d bytes", (char*) indent,

libs/hwui/DisplayListRenderer.h

@@ -656,18 +656,16 @@ class DisplayListRenderer: public OpenGLRenderer {
         if (reject) {
             mWriter.writeInt(OP_MAY_BE_SKIPPED_MASK | drawOp);
             mWriter.writeInt(0xdeaddead);
-            uint32_t* location = reject ?
-                    mWriter.peek32(mWriter.size() - sizeof(int32_t)) : NULL;
-            return location;
+            mBufferSize = mWriter.size();
+            return mWriter.peek32(mBufferSize - sizeof(int32_t));
         }
         mWriter.writeInt(drawOp);
         return NULL;
     }
 
     inline void addSkip(uint32_t* location) {
         if (location) {
-            *location = (int32_t) (mWriter.peek32(
-                    mWriter.size() - sizeof(int32_t)) - location);
+            *location = (int32_t) (mWriter.size() - mBufferSize);
         }
     }
 
@@ -822,6 +820,7 @@ class DisplayListRenderer: public OpenGLRenderer {
     Vector<SkMatrix*> mMatrices;
 
     SkWriter32 mWriter;
+    uint32_t mBufferSize;
 
     int mRestoreSaveCount;