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 54 matching lines @@
 
 // Manages a rendering target (framebuffer + attachment) for a canvas.  Can publish its rendering
 // results to a WebLayer for compositing.
 class PLATFORM_EXPORT DrawingBuffer : public RefCounted<DrawingBuffer>, public WebExternalTextureLayerClient  {
     WTF_MAKE_NONCOPYABLE(DrawingBuffer);
 public:
     enum PreserveDrawingBuffer {
         Preserve,
         Discard
     };
+    enum WebGLVersion {
+        WebGL1,
+        WebGL2,
+    };
 
     static PassRefPtr<DrawingBuffer> create(
         std::unique_ptr<WebGraphicsContext3DProvider>,
         const IntSize&,
         bool premultipliedAlpha,
         bool wantAlphaChannel,
         bool wantDepthBuffer,
         bool wantStencilBuffer,
         bool wantAntialiasing,
-        PreserveDrawingBuffer);
+        PreserveDrawingBuffer,
+        WebGLVersion);
     static void forceNextDrawingBufferCreationToFail();
 
     ~DrawingBuffer() override;
 
     // Destruction will be completed after all mailboxes are released.
     void beginDestruction();
 
     // Issues a glClear() on all framebuffers associated with this DrawingBuffer. The caller is responsible for
     // making the context current and setting the clear values and masks. Modifies the framebuffer binding.
     void clearFramebuffers(GLbitfield clearMask);
@@ skipping 125 matching lines @@
     void addNewMailboxCallback(std::unique_ptr<WTF::Closure> closure) { m_newMailboxCallback = std::move(closure); }
 
 protected: // For unittests
     DrawingBuffer(
         std::unique_ptr<WebGraphicsContext3DProvider>,
         std::unique_ptr<Extensions3DUtil>,
         bool discardFramebufferSupported,
         bool wantAlphaChannel,
         bool premultipliedAlpha,
         PreserveDrawingBuffer,
+        WebGLVersion,
         bool wantsDepth,
         bool wantsStencil);
 
     bool initialize(const IntSize&, bool useMultisampling);
 
 private:
     // All parameters necessary to generate the texture that will be passed to
     // prepareMailbox.
     struct TextureParameters {
         DISALLOW_NEW();
         GLenum target = 0;
         GLenum internalColorFormat = 0;
 
         // The internal color format used when allocating storage for the
         // texture. This may be different from internalColorFormat if RGB
         // emulation is required.
         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);
+    // Allocate a storage texture if possible. Otherwise, allocate a regular texture.
+    void allocateConditionallyImmutableTexture(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 14 matching lines @@
     // renderbuffer, which is resolved before any read operations or swaps.
     bool wantExplicitResolve();
 
     // Whether the WebGL client wants a depth or stencil buffer.
     bool wantDepthOrStencil();
 
     // The format to use when creating a multisampled renderbuffer.
     GLenum getMultisampledRenderbufferFormat();
 
     const PreserveDrawingBuffer m_preserveDrawingBuffer;
+    const WebGLVersion m_webGLVersion;
     bool m_scissorEnabled = false;
     GLuint m_texture2DBinding = 0;
     GLuint m_drawFramebufferBinding = 0;
     GLuint m_readFramebufferBinding = 0;
     GLuint m_renderbufferBinding = 0;
     GLenum m_activeTextureUnit = GL_TEXTURE0;
     GLfloat m_clearColor[4];
     GLboolean m_colorMask[4];
 
     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