[Command buffer] CopyTexSubImage3D: Copying pixels outside of framebuffer should be untouched

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 68b894846bb0ff89ffbdd837869f1f4f0492aaf6..c97b9c357d114ab3acb0003177ea7dabd9cd4e7c 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -13264,19 +13264,61 @@ void GLES2DecoderImpl::DoCopyTexSubImage3D(
     return;
   }
 
-  // For 3D textures, we always clear the entire texture. See the code in
-  // TextureManager::ValidateAndDoTexSubImage for TexSubImage3D.
+  ScopedResolvedFrameBufferBinder binder(this, false, true);
+  gfx::Size size = GetBoundReadFrameBufferSize();
+  GLint copyX = 0;
+  GLint copyY = 0;
+  GLint copyWidth = 0;
+  GLint copyHeight = 0;
+  Clip(x, width, size.width(), &copyX, &copyWidth);
+  Clip(y, height, size.height(), &copyY, &copyHeight);
+
+  GLint dx = copyX - x;
+  GLint dy = copyY - y;
+  GLint destX = xoffset + dx;
+  GLint destY = yoffset + dy;
+  // For 3D textures, we always clear the entire texture to 0 if it is not
+  // cleared. See the code in TextureManager::ValidateAndDoTexSubImage
+  // for TexSubImage3D.
   if (!texture->IsLevelCleared(target, level)) {
     texture_manager()->ClearTextureLevel(this, texture_ref, target, level);
     DCHECK(texture->IsLevelCleared(target, level));
+  } else {
+    // For any pixel lying outside the framebuffer, all channels of the
+    // associated texel are initialized to 0.
+    if (x != copyX || y != copyY ||
+        width != copyWidth || height != copyHeight) {
+      uint32_t pixels_size = 0;
+      GLenum format =
+          TextureManager::ExtractFormatFromStorageFormat(internal_format);
+      GLenum type =
+          TextureManager::ExtractTypeFromStorageFormat(internal_format);
+      // The internal_format was selected and validated previously by either
+      // a TexImage3D or a TexStorage3D. So the format / type pair is valid.
+      DCHECK(format && type);
+
+      if (!GLES2Util::ComputeImageDataSizes(
+          width, height, 1, format, type,
+          state_.unpack_alignment, &pixels_size, NULL, NULL)) {
+        LOCAL_SET_GL_ERROR(GL_OUT_OF_MEMORY, func_name, "dimensions too large");
+        return;
+      }
+
+      // some part was clipped so clear the rect.
+      std::unique_ptr<char[]> zero(new char[pixels_size]);
+      memset(zero.get(), 0, pixels_size);
+      glTexSubImage3D(target, level, xoffset, yoffset, zoffset,
+                      width, height, 1, format, type, zero.get());

[Ken Russell (switch to Gerrit), 2016/08/12 17:50:27]

Per comments above and on the bug: let's change the spec of CopyTexSubImage3D in
WebGL 2.0 to match the spec of CopyTexSubImage2D in WebGL 1.0 -- i.e., leave the
pixels outside the framebuffer untouched.
https://github.com/KhronosGroup/WebGL/pull/1965 will make this change.

[yunchao, 2016/08/12 23:59:43]

Acknowledged.

+    }
   }
 
   // TODO(yunchao): Follow-up CLs are necessary. For instance:
   // 1. emulation of unsized formats in core profile
-  // 2. out-of-bounds reading, etc.
 
-  glCopyTexSubImage3D(target, level, xoffset, yoffset, zoffset, x, y, width,
-                      height);
+  if (copyHeight > 0 && copyWidth > 0) {
+    glCopyTexSubImage3D(target, level, destX, destY, zoffset,
+                        copyX, copyY, copyWidth, copyHeight);
+  }
 
   // This may be a slow command.  Exit command processing to allow for
   // context preemption and GPU watchdog checks.