Add offset arguments to readPixels and compressedTex* per WebGL 2.0 spec.

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 4043 matching lines @@
   return true;
 }
 
 void WebGLRenderingContextBase::readPixels(GLint x,
                                            GLint y,
                                            GLsizei width,
                                            GLsizei height,
                                            GLenum format,
                                            GLenum type,
                                            DOMArrayBufferView* pixels) {
+  readPixelsHelper(x, y, width, height, format, type, pixels, 0);
+}
+
+void WebGLRenderingContextBase::readPixelsHelper(GLint x,
+                                                 GLint y,
+                                                 GLsizei width,
+                                                 GLsizei height,
+                                                 GLenum format,
+                                                 GLenum type,
+                                                 DOMArrayBufferView* pixels,
+                                                 GLuint offset) {
   if (isContextLost())
     return;
   // Due to WebGL's same-origin restrictions, it is not possible to
   // taint the origin using the WebGL API.
   ASSERT(canvas()->originClean());
   // Validate input parameters.
   if (!pixels) {
     synthesizeGLError(GL_INVALID_VALUE, "readPixels",
                       "no destination ArrayBufferView");
     return;
   }
+  CheckedNumeric<GLuint> offsetInBytes = offset;
+  offsetInBytes *= pixels->typeSize();
+  if (!offsetInBytes.IsValid() ||
+      offsetInBytes.ValueOrDie() > pixels->byteLength()) {
+    synthesizeGLError(GL_INVALID_VALUE, "readPixels",
+                      "destination offset out of range");
+    return;
+  }
   const char* reason = "framebuffer incomplete";
   WebGLFramebuffer* framebuffer = getReadFramebufferBinding();
   if (framebuffer &&
       framebuffer->checkDepthStencilStatus(&reason) !=
           GL_FRAMEBUFFER_COMPLETE) {
     synthesizeGLError(GL_INVALID_FRAMEBUFFER_OPERATION, "readPixels", reason);
     return;
   }
   if (!validateReadPixelsFuncParameters(
           width, height, format, type, pixels,
-          static_cast<long long>(pixels->byteLength())))
+          static_cast<long long>(pixels->byteLength() -
+                                 offsetInBytes.ValueOrDie()))) {
     return;
-
+  }
   clearIfComposited();
-  void* data = pixels->baseAddress();
-
+  uint8_t* data =
+      static_cast<uint8_t*>(pixels->baseAddress()) + offsetInBytes.ValueOrDie();
   {
     ScopedDrawingBufferBinder binder(drawingBuffer(), framebuffer);
     contextGL()->ReadPixels(x, y, width, height, format, type, data);
   }
 }
 
 void WebGLRenderingContextBase::renderbufferStorageImpl(
     GLenum target,
     GLsizei samples,
     GLenum internalformat,
@@ skipping 3508 matching lines @@
 
 void WebGLRenderingContextBase::getHTMLOrOffscreenCanvas(
     HTMLCanvasElementOrOffscreenCanvas& result) const {
   if (canvas())
     result.setHTMLCanvasElement(canvas());
   else
     result.setOffscreenCanvas(getOffscreenCanvas());
 }
 
 }  // namespace blink