Reland of Untouch out of bound pixels for CopyTexSubImage2D

gpu/command_buffer/service/gles2_cmd_decoder.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
@@ skipping 11379 matching lines @@
         LOCAL_SET_GL_ERROR(GL_OUT_OF_MEMORY, "glCopyTexSubImage2D",
                            "dimensions too big");
         return;
       }
     }
   } else {
     // Write all pixels in below.
     texture_manager()->SetLevelCleared(texture_ref, target, level, true);
   }
 
-  if (copyX != x ||
-      copyY != y ||
-      copyWidth != width ||
-      copyHeight != height) {
-    // some part was clipped so clear the sub rect.
-    uint32_t pixels_size = 0;
-    if (!GLES2Util::ComputeImageDataSizes(
-        width, height, 1, format, type, state_.unpack_alignment, &pixels_size,
-        NULL, NULL)) {
-      LOCAL_SET_GL_ERROR(
-          GL_INVALID_VALUE, "glCopyTexSubImage2D", "dimensions too large");
-      return;
-    }
-    scoped_ptr<char[]> zero(new char[pixels_size]);
-    memset(zero.get(), 0, pixels_size);
-    glTexSubImage2D(
-        target, level, xoffset, yoffset, width, height,
-        format, type, zero.get());
-  }

[Zhenyao Mo, 2016/01/14 18:13:37]

Look at the code above SetLevelClearedRect(), since now we leave out-of-bounds
pixels untouched, then we need to take that into consideration for the cleared
rect. Otherwise we could end up leaking vram.

[qiankun, 2016/01/19 16:07:31]

Thanks for pointing this. I updated the CL. PTAL. 

-
   if (copyHeight > 0 && copyWidth > 0) {
     GLint dx = copyX - x;
     GLint dy = copyY - y;
     GLint destX = xoffset + dx;
     GLint destY = yoffset + dy;
     glCopyTexSubImage2D(target, level,
                         destX, destY, copyX, copyY,
                         copyWidth, copyHeight);
   }
 
@@ skipping 4150 matching lines @@
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "base/macros.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu