Pepper 3D API changes:

ppapi/c/dev/ppb_graphics_3d_dev.h

 /* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef PPAPI_C_DEV_PPB_GRAPHICS_3D_DEV_H_
 #define PPAPI_C_DEV_PPB_GRAPHICS_3D_DEV_H_
 
 #include "ppapi/c/dev/pp_graphics_3d_dev.h"
 
 #include "ppapi/c/pp_bool.h"
@@ skipping 10 matching lines @@
 // context = g3d->Create(instance, attribs, &context);
 // inst->BindGraphics(instance, context);
 //
 // // Present one frame.
 // gles2->Clear(context, GL_COLOR_BUFFER);
 // g3d->SwapBuffers(context);
 //
 // // Shutdown.
 // core->ReleaseResource(context);
 
-#define PPB_GRAPHICS_3D_DEV_INTERFACE_0_8 "PPB_Graphics3D(Dev);0.8"
-#define PPB_GRAPHICS_3D_DEV_INTERFACE PPB_GRAPHICS_3D_DEV_INTERFACE_0_8
+#define PPB_GRAPHICS_3D_DEV_INTERFACE_0_9 "PPB_Graphics3D(Dev);0.9"
+#define PPB_GRAPHICS_3D_DEV_INTERFACE PPB_GRAPHICS_3D_DEV_INTERFACE_0_9
 
 struct PPB_Graphics3D_Dev {
+  // Retrieves the maximum supported value for the given attribute.
+  //
+  // This function may be used to check if a particular attribute value is
+  // supported before attempting to create a context.
+  // Attributes that can be queried for include:
+  // - PP_GRAPHICS3DATTRIB_ALPHA_SIZE
+  // - PP_GRAPHICS3DATTRIB_BLUE_SIZE
+  // - PP_GRAPHICS3DATTRIB_GREEN_SIZE
+  // - PP_GRAPHICS3DATTRIB_RED_SIZE
+  // - PP_GRAPHICS3DATTRIB_DEPTH_SIZE
+  // - PP_GRAPHICS3DATTRIB_STENCIL_SIZE
+  // - PP_GRAPHICS3DATTRIB_SAMPLES
+  // - PP_GRAPHICS3DATTRIB_SAMPLE_BUFFERS
+  // - PP_GRAPHICS3DATTRIB_WIDTH
+  // - PP_GRAPHICS3DATTRIB_HEIGHT
+  //
+  // On failure the following error codes may be returned:
+  // - PP_ERROR_BADRESOURCE if instance is invalid.
+  // - PP_ERROR_BADARGUMENT if attribute is invalid or value is NULL
+  int32_t (*GetAttribMaxValue)(PP_Resource instance,
+                               int32_t attribute, int32_t* value);
+
   // Creates and initializes a rendering context and returns a handle to it.
   // The returned context is off-screen to start with. It must be attached to
   // a plugin instance using PPB_Instance::BindGraphics to draw on the web page.
   //
   // If share_context is not NULL, then all shareable data, as defined
   // by the client API (note that for OpenGL and OpenGL ES, shareable data
   // excludes texture objects named 0) will be shared by share_context, all
   // other contexts share_context already shares with, and the newly created
   // context. An arbitrary number of PPB_Graphics3D_Dev can share data in
   // this fashion.
@@ skipping 29 matching lines @@
   //
   // On failure NULL resource is returned.
   PP_Resource (*Create)(PP_Instance instance,
                         PP_Resource share_context,
                         const int32_t* attrib_list);
 
   // Returns PP_TRUE if the given resource is a valid PPB_Graphics3D_Dev,
   // PP_FALSE if it is an invalid resource or is a resource of another type.
   PP_Bool (*IsGraphics3D)(PP_Resource resource);
 
-  // Retrieves the values for each attribute in attrib_list. The list
+  // Retrieves the value for each attribute in attrib_list. The list
   // has the same structure as described for PPB_Graphics3D_Dev::Create.
   // It is both input and output structure for this function.
   //
   // All attributes specified in PPB_Graphics3D_Dev::Create can be queried for.
   // On failure the following error codes may be returned:
   // - PP_ERROR_BADRESOURCE if context is invalid.
-  // - PP_GRAPHICS3DERROR_BAD_ATTRIBUTE if any attribute in the attrib_list
-  //   is not a valid attribute
+  // - PP_ERROR_BADARGUMENT if attrib_list is NULL or any attribute in the
+  //   attrib_list is not a valid attribute.
   //
   // Example usage: To get the values for rgb bits in the color buffer,
   // this function must be called as following:
   // int attrib_list[] = {PP_GRAPHICS3DATTRIB_RED_SIZE, 0,
   //                      PP_GRAPHICS3DATTRIB_GREEN_SIZE, 0,
   //                      PP_GRAPHICS3DATTRIB_BLUE_SIZE, 0,
   //                      PP_GRAPHICS3DATTRIB_NONE};
   // GetAttribs(context, attrib_list);
   // int red_bits = attrib_list[1];
   // int green_bits = attrib_list[3];
   // int blue_bits = attrib_list[5];
   int32_t (*GetAttribs)(PP_Resource context, int32_t* attrib_list);
 
   // Sets the values for each attribute in attrib_list. The list
   // has the same structure as described for PPB_Graphics3D_Dev::Create.
   //
   // Attributes that can be specified are:
   // - PP_GRAPHICS3DATTRIB_SWAP_BEHAVIOR
+  //
+  // On failure the following error codes may be returned:
+  // - PP_ERROR_BADRESOURCE if context is invalid.
+  // - PP_ERROR_BADARGUMENT if attrib_list is NULL or any attribute in the
+  //   attrib_list is not a valid attribute.
   int32_t (*SetAttribs)(PP_Resource context, int32_t* attrib_list);
 
+  // The recoverable error conditions that have no side effect are
+  // detected and returned immediately by all functions in this interface.
+  // In addition the implementation may get into a fatal state while
+  // processing a command. In this case the application must detroy the
+  // context and reinitialize client API state and objects to continue
+  // rendering. Note that the same error code is also returned in the swap

[brettw, 2011/09/02 20:21:45]

It's not clear to me when I'm supposed to call this function.

[alokp, 2011/09/02 21:41:02]

The context may get lost anytime. It may go out of memory when attempting to
resize the backing surface. An application may call this function after resize.
Although not recommended, but an application may even call it at the beginning
of a frame to make sure it can be rendered to.

If your question is "why is it part of the API when the error code is already
returned by SwapBuffers?", then please see the discussion here -
http://codereview.chromium.org/7530010. Antoine wanted to support one particular
use case - "In the case that it's CPU-costly to draw a frame, the user may want
to check for the result of resize before starting a draw cycle, paying for the
round trip".

I think that most applications will not call this function ever. They will just
check the error code in SwapBuffers callback.

[brettw, 2011/09/02 22:14:24]

Then I'd like to add to the comment that this returns the same error code
provided by the SwapBuffers callback. If this function can return some data
before the callback occurs, can we mention this?

My problem is that as somebody thinking about using this API, it's not clear if
I should be calling this function, and when I should be calling it. I might be
tempted to call it all the time to make sure there's no error, which would be
incorrect. We at least need to have enough info here so that the people who
don't need this function know they don't need it.

[alokp, 2011/09/02 23:45:07]

I already have this in the comment - "Note that the same error code is also
returned in the swap buffers callback". Is that what you were looking for?
 
I agree it is confusing and could lead to many applications calling a
synchronous function unnecessarily. I have tried to make it clearer by adding
more documentation to GetError and SwapBuffers, but still think we should remove
this from V1. SwapBuffers callback covers most use cases.

+  // buffers callback.
+  //
+  // The following error codes may be returned:
+  // - PP_ERROR_NOMEMORY
+  // - PP_ERROR_CONTEXT_LOST
+  int32_t (*GetError)(PP_Resource context);
+
   // Resizes the backing surface for context.
   //
   // On failure the following error codes may be returned:
   // - PP_ERROR_BADRESOURCE if context is invalid.
   // - PP_ERROR_BADARGUMENT if the value specified for width or height
   //   is less than zero.
   //
   // If the surface could not be resized due to insufficient resources,
   // PP_ERROR_NOMEMORY error is returned on the next SwapBuffers callback.
   int32_t (*ResizeBuffers)(PP_Resource context,
                            int32_t width, int32_t height);
 
   // Makes the contents of the color buffer available for compositing.
   // This function has no effect on off-screen surfaces - ones not bound
   // to any plugin instance. The contents of ancillary buffers are always
   // undefined after calling SwapBuffers. The contents of the color buffer are
   // undefined if the value of the PP_GRAPHICS3DATTRIB_SWAP_BEHAVIOR attribute
   // of context is not PP_GRAPHICS3DATTRIB_BUFFER_PRESERVED.
   //
-  // SwapBuffers performs an implicit flush operation on context.
-  //
-  // This functions can run in two modes:
-  // - In synchronous mode, you specify NULL for the callback and the callback
-  //   data. This function will block the calling thread until the image has
-  //   been painted to the screen. It is not legal to block the main thread of
-  //   the plugin, you can use synchronous mode only from background threads.
-  // - In asynchronous mode, you specify a callback function and the argument
-  //   for that callback function. The callback function will be executed on
-  //   the calling thread when the image has been painted to the screen. While
-  //   you are waiting for a Flush callback, additional calls to Flush will
-  //   fail.
+  // SwapBuffers runs in asynchronous mode. Specify a callback function and the
+  // argument for that callback function. The callback function will be executed
+  // on the calling thread after the color buffer has been composited with
+  // rest of the html page. While you are waiting for a SwapBuffers callback,
+  // additional calls to SwapBuffers will fail.
   //
   // Because the callback is executed (or thread unblocked) only when the
   // plugin's current state is actually on the screen, this function provides a
   // way to rate limit animations. By waiting until the image is on the screen
   // before painting the next frame, you can ensure you're not generating
   // updates faster than the screen can be updated.
+  //
+  // SwapBuffers performs an implicit flush operation on context.
+  // If the context gets into an unrecoverable error condition while
+  // processing a command, the error code will be returned as the argument
+  // for the callback.
+  //
+  // On failure the following error codes may be returned:
+  // - PP_ERROR_BADRESOURCE if context is invalid.
+  // - PP_ERROR_BADARGUMENT if callback is invalid.
   int32_t (*SwapBuffers)(PP_Resource context,
                          struct PP_CompletionCallback callback);
 };
 
 #endif  /* PPAPI_C_DEV_PPB_GRAPHICS_3D_DEV_H_ */