Fix a bug where PIXEL_UNPACK_BUFFER is cleared but never restored.

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 1570 matching lines @@
   return ImageData::create(
       IntSize(width, height),
       DOMUint8ClampedArray::create(imageDataPixels, 0,
                                    imageDataPixels->byteLength()));
 }
 
 void WebGLRenderingContextBase::reshape(int width, int height) {
   if (isContextLost())
     return;
 
+  GLint buffer = 0;
   if (isWebGL2OrHigher()) {
-    contextGL()->BindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
+    // This query returns client side cached binding, so it's trivial.
+    // If it changes in the future, such query is heavy and should be avoided.
+    contextGL()->GetIntegerv(GL_PIXEL_UNPACK_BUFFER_BINDING, &buffer);
+    if (buffer) {
+      contextGL()->BindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
+    }
   }
 
   // This is an approximation because at WebGLRenderingContextBase level we
   // don't know if the underlying FBO uses textures or renderbuffers.
   GLint maxSize = std::min(m_maxTextureSize, m_maxRenderbufferSize);
   GLint maxWidth = std::min(maxSize, m_maxViewportDims[0]);
   GLint maxHeight = std::min(maxSize, m_maxViewportDims[1]);
   width = clamp(width, 1, maxWidth);
   height = clamp(height, 1, maxHeight);
 
   // Limit drawing buffer area to 4k*4k to avoid memory exhaustion. Width or
   // height may be larger than 4k as long as it's within the max viewport
   // dimensions and total area remains within the limit.
   // For example: 5120x2880 should be fine.
   const int maxArea = 4096 * 4096;
   int currentArea = width * height;
   if (currentArea > maxArea) {
     // If we've exceeded the area limit scale the buffer down, preserving
     // ascpect ratio, until it fits.
     float scaleFactor =
         sqrtf(static_cast<float>(maxArea) / static_cast<float>(currentArea));
     width = std::max(1, static_cast<int>(width * scaleFactor));
     height = std::max(1, static_cast<int>(height * scaleFactor));
   }
 
   // We don't have to mark the canvas as dirty, since the newly created image
   // buffer will also start off clear (and this matches what reshape will do).
   drawingBuffer()->resize(IntSize(width, height));
+
+  if (buffer) {
+    contextGL()->BindBuffer(GL_PIXEL_UNPACK_BUFFER,
+                            static_cast<GLuint>(buffer));
+  }
 }
 
 int WebGLRenderingContextBase::drawingBufferWidth() const {
   return isContextLost() ? 0 : drawingBuffer()->size().width();
 }
 
 int WebGLRenderingContextBase::drawingBufferHeight() const {
   return isContextLost() ? 0 : drawingBuffer()->size().height();
 }
 
@@ skipping 6196 matching lines @@
 
 void WebGLRenderingContextBase::getHTMLOrOffscreenCanvas(
     HTMLCanvasElementOrOffscreenCanvas& result) const {
   if (canvas())
     result.setHTMLCanvasElement(canvas());
   else
     result.setOffscreenCanvas(offscreenCanvas());
 }
 
 }  // namespace blink