Reland "webgl: use immutable texture for the default FBO."

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

 /*
  * Copyright (c) 2010, Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 235 matching lines @@
         GLenum creationInternalColorFormat = 0;
         GLenum colorFormat = 0;
     };
 
     // If we used CHROMIUM_image as the backing storage for our buffers,
     // we need to know the mapping from texture id to image.
     struct TextureInfo {
         DISALLOW_NEW();
         GLuint textureId = 0;
         GLuint imageId = 0;
+        bool immutable = false;
 
         // A GpuMemoryBuffer is a concept that the compositor understands. and
         // is able to operate on. The id is scoped to renderer process.
         GLint gpuMemoryBufferId = -1;
 
         TextureParameters parameters;
     };
 
     struct MailboxInfo : public RefCounted<MailboxInfo> {
         WTF_MAKE_NONCOPYABLE(MailboxInfo);
@@ skipping 48 matching lines @@
         ReadbackSkia
     };
 
     // Helper function which does a readback from the currently-bound
     // framebuffer into a buffer of a certain size with 4-byte pixels.
     void readBackFramebuffer(unsigned char* pixels, int width, int height, ReadbackOrder, WebGLImageConversion::AlphaOp);
 
     // Helper function to flip a bitmap vertically.
     void flipVertically(uint8_t* data, int width, int height);
 
-    // Helper to texImage2D with pixel==0 case: pixels are initialized to 0.
-    // By default, alignment is 4, the OpenGL default setting.
-    void texImage2DResourceSafe(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, GLint alignment = 4);
+    // Create a storage texture if possible.
+    // Return true if a storage texture is created.
+    // Return false if a regular texture is created.
+    bool createStorageTextureIfPossible(GLenum target, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type);
     // Allocate buffer storage to be sent to compositor using either texImage2D or CHROMIUM_image based on available support.
     void deleteChromiumImageForTexture(TextureInfo*);
 
     // If RGB emulation is required, then the CHROMIUM image's alpha channel
     // must be immediately cleared after it is bound to a texture. Nothing
     // should be allowed to change the alpha channel after this.
     void clearChromiumImageAlpha(const TextureInfo&);
 
     // Tries to create a CHROMIUM_image backed texture if
     // RuntimeEnabledFeatures::webGLImageChromiumEnabled() is true. On failure,
@@ skipping 32 matching lines @@
 
     std::unique_ptr<WebGraphicsContext3DProvider> m_contextProvider;
     // Lifetime is tied to the m_contextProvider.
     gpu::gles2::GLES2Interface* m_gl;
     std::unique_ptr<Extensions3DUtil> m_extensionsUtil;
     IntSize m_size = { -1, -1 };
     const bool m_discardFramebufferSupported;
     const bool m_wantAlphaChannel;
     const bool m_premultipliedAlpha;
     bool m_hasImplicitStencilBuffer = false;
+    bool m_storageTextureSupported = false;
     struct FrontBufferInfo {
         TextureInfo texInfo;
         WebExternalTextureMailbox mailbox;
     };
     FrontBufferInfo m_frontColorBuffer;
 
     std::unique_ptr<WTF::Closure> m_newMailboxCallback;
 
     // This is used when the user requests either a depth or stencil buffer.
     GLuint m_depthStencilBuffer = 0;
@@ skipping 55 matching lines @@
     // used to resize the Canvas.
     SkBitmap m_resizingBitmap;
 
     // Used to flip a bitmap vertically.
     Vector<uint8_t> m_scanline;
 };
 
 } // namespace blink
 
 #endif // DrawingBuffer_h