// Copyright 2015-2021 The Khronos Group Inc.
//
// SPDX-License-Identifier: CC-BY-4.0

include::{generated}/meta/{refprefix}VK_EXT_debug_report.txt[]

=== Other Extension Metadata

*Last Modified Date*::
    2020-12-14
*IP Status*::
    No known IP claims.
*Contributors*::
  - Courtney Goeltzenleuchter, LunarG
  - Dan Ginsburg, Valve
  - Jon Ashburn, LunarG
  - Mark Lobodzinski, LunarG

=== Description

Due to the nature of the Vulkan interface, there is very little error
information available to the developer and application.
By enabling optional validation layers and using the `VK_EXT_debug_report`
extension, developers can: obtain much more detailed feedback on the
application's use of Vulkan.
This extension defines a way for layers and the implementation to call back
to the application for events of interest to the application.

include::{generated}/interfaces/VK_EXT_debug_report.txt[]

=== Examples

`VK_EXT_debug_report` allows an application to register multiple callbacks
with the validation layers.
Some callbacks may log the information to a file, others may cause a debug
break point or other application defined behavior.
An application can: register callbacks even when no validation layers are
enabled, but they will only be called for loader and, if implemented, driver
events.

To capture events that occur while creating or destroying an instance an
application can: link a slink:VkDebugReportCallbackCreateInfoEXT structure
to the pname:pNext element of the slink:VkInstanceCreateInfo structure given
to flink:vkCreateInstance.

Example uses: Create three callback objects.
One will log errors and warnings to the debug console using Windows
code:OutputDebugString.
The second will cause the debugger to break at that callback when an error
happens and the third will log warnings to stdout.
[source,c++]
------------------------------------------------------------------------------
    VkResult res;
    VkDebugReportCallbackEXT cb1, cb2, cb3;

    VkDebugReportCallbackCreateInfoEXT callback1 = {
            VK_STRUCTURE_TYPE_DEBUG_REPORT_CALLBACK_CREATE_INFO_EXT,    // sType
            NULL,                                                       // pNext
            VK_DEBUG_REPORT_ERROR_BIT_EXT |                             // flags
            VK_DEBUG_REPORT_WARNING_BIT_EXT,
            myOutputDebugString,                                        // pfnCallback
            NULL                                                        // pUserData
    };
    res = vkCreateDebugReportCallbackEXT(instance, &callback1, &cb1);
    if (res != VK_SUCCESS)
       /* Do error handling for VK_ERROR_OUT_OF_MEMORY */

    callback.flags = VK_DEBUG_REPORT_ERROR_BIT_EXT;
    callback.pfnCallback = myDebugBreak;
    callback.pUserData = NULL;
    res = vkCreateDebugReportCallbackEXT(instance, &callback, &cb2);
    if (res != VK_SUCCESS)
       /* Do error handling for VK_ERROR_OUT_OF_MEMORY */

    VkDebugReportCallbackCreateInfoEXT callback3 = {
            VK_STRUCTURE_TYPE_DEBUG_REPORT_CALLBACK_CREATE_INFO_EXT,    // sType
            NULL,                                                       // pNext
            VK_DEBUG_REPORT_WARNING_BIT_EXT,                            // flags
            mystdOutLogger,                                             // pfnCallback
            NULL                                                        // pUserData
    };
    res = vkCreateDebugReportCallbackEXT(instance, &callback3, &cb3);
    if (res != VK_SUCCESS)
       /* Do error handling for VK_ERROR_OUT_OF_MEMORY */

    ...

    /* remove callbacks when cleaning up */
    vkDestroyDebugReportCallbackEXT(instance, cb1);
    vkDestroyDebugReportCallbackEXT(instance, cb2);
    vkDestroyDebugReportCallbackEXT(instance, cb3);
------------------------------------------------------------------------------

[NOTE]
.Note
====
In the initial release of the `VK_EXT_debug_report` extension, the token
ename:VK_STRUCTURE_TYPE_DEBUG_REPORT_CREATE_INFO_EXT was used.
Starting in version 2 of the extension branch,
ename:VK_STRUCTURE_TYPE_DEBUG_REPORT_CALLBACK_CREATE_INFO_EXT is used
instead for consistency with Vulkan naming rules.
The older enum is still available for backwards compatibility.
====

[NOTE]
.Note
====
In the initial release of the `VK_EXT_debug_report` extension, the token
ename:VK_DEBUG_REPORT_OBJECT_TYPE_DEBUG_REPORT_EXT was used.
Starting in version 8 of the extension branch,
ename:VK_DEBUG_REPORT_OBJECT_TYPE_DEBUG_REPORT_CALLBACK_EXT_EXT is used
instead for consistency with Vulkan naming rules.
The older enum is still available for backwards compatibility.
====


=== Issues

1) What is the hierarchy / seriousness of the message flags? E.g.
etext:ERROR > etext:WARN > etext:PERF_WARN ...

*RESOLVED*: There is no specific hierarchy.
Each bit is independent and should be checked via bitwise AND.
For example:

[source,c++]
----------------------------------------
    if (localFlags & VK_DEBUG_REPORT_ERROR_BIT_EXT) {
        process error message
    }
    if (localFlags & VK_DEBUG_REPORT_DEBUG_BIT_EXT) {
        process debug message
    }
----------------------------------------

The validation layers do use them in a hierarchical way (etext:ERROR >
etext:WARN > etext:PERF, etext:WARN > etext:DEBUG > etext:INFO) and they (at
least at the time of this writing) only set one bit at a time.
But it is not a requirement of this extension.

It is possible that a layer may intercept and change, or augment the flags
with extension values the application's debug report handler may not be
familiar with, so it is important to treat each flag independently.

2) Should there be a VU requiring
slink:VkDebugReportCallbackCreateInfoEXT::pname:flags to be non-zero?

*RESOLVED*: It may not be very useful, but we do not need VU statement
requiring the sname:VkDebugReportCallbackCreateInfoEXT::pname:msgFlags at
create-time to be non-zero.
One can imagine that apps may prefer it as it allows them to set the mask as
desired - including nothing - at runtime without having to check.

3) What is the difference between ename:VK_DEBUG_REPORT_DEBUG_BIT_EXT and
ename:VK_DEBUG_REPORT_INFORMATION_BIT_EXT?

*RESOLVED*: ename:VK_DEBUG_REPORT_DEBUG_BIT_EXT specifies information that
could be useful debugging the Vulkan implementation itself.

4) How do you compare handles returned by the debug_report callback to the
application's handles?

*RESOLVED*: Due to the different nature of dispatchable and nondispatchable
handles there is no generic way (that we know of) that works for common
compilers with 32bit, 64bit, C and C++.
We recommend applications use the same cast that the validation layers use:
+
[source,c++]
----
reinterpret_cast<uint64_t &>(dispatchableHandle)
(uint64_t)(nondispatchableHandle)
----
+
This does require that the app treat dispatchable and nondispatchable
handles differently.

=== Version History

 * Revision 1, 2015-05-20 (Courtney Goetzenleuchter)
   - Initial draft, based on LunarG KHR spec, other KHR specs

 * Revision 2, 2016-02-16 (Courtney Goetzenleuchter)
   - Update usage, documentation

 * Revision 3, 2016-06-14 (Courtney Goetzenleuchter)
   - Update VK_EXT_DEBUG_REPORT_SPEC_VERSION to indicate added support for
     vkCreateInstance and vkDestroyInstance

 * Revision 4, 2016-12-08 (Mark Lobodzinski)
   - Added Display_KHR, DisplayModeKHR extension objects
   - Added ObjectTable_NVX, IndirectCommandsLayout_NVX extension objects
   - Bumped spec revision
   - Retroactively added version history

 * Revision 5, 2017-01-31 (Baldur Karlsson)
   - Moved definition of elink:VkDebugReportObjectTypeEXT from debug marker
     chapter

 * Revision 6, 2017-01-31 (Baldur Karlsson)
   - Added VK_DEBUG_REPORT_OBJECT_TYPE_DESCRIPTOR_UPDATE_TEMPLATE_KHR_EXT

 * Revision 7, 2017-04-20 (Courtney Goeltzenleuchter)
   - Clarify wording and address questions from developers.

 * Revision 8, 2017-04-21 (Courtney Goeltzenleuchter)
   - Remove unused enum VkDebugReportErrorEXT

 * Revision 9, 2017-09-12 (Tobias Hector)
   - Added interactions with Vulkan 1.1

 * Revision 10, 2020-12-14 (Courtney Goetzenleuchter)
   - Add issue 4 discussing matching handles returned by the extension,
     based on suggestion in public issue 368.
