Vulkan global pipeline is unable to distinguish user render-pass vs gw renderpass.

[FunMiles]

Version/Branch of Dear ImGui:

Version: commit 9a363c7c922c04440d0b1901a61e14b796c84fae
Branch: docking
Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_vulkan.cpp + imgui_impl_glfw.cpp
Compiler: clang++
Operating System: Mac OS X / Linux

My Issue/Question:

I am using the docking branch of Dear ImGui in a code of mine. Everything works fine but when one of the Dear ImGui windows is given a new system window, the Vulkan Khronos debug layer gives an error:

Validation Error: [ VUID-vkCmdDrawIndexed-renderPass-02684 ] Object 0: handle = 0x5c000000005c, type = VK_OBJECT_TYPE_RENDER_PASS; Object 1: handle = 0xe000000000e, type = VK_OBJECT_TYPE_RENDER_PASS; | MessageID = 0x8cb637c2 | vkCmdDrawIndexed(): RenderPasses incompatible between active render pass w/ VkRenderPass 0x5c000000005c[] and pipeline state object w/ VkRenderPass 0xe000000000e[] Attachment 4294967295 is not compatible with 1: The first is unused while the second is not.. The Vulkan spec states: The current render pass must
be compatible with the renderPass member of the VkGraphicsPipelineCreateInfo structure specified when creating the VkPipeline bound to VK_PIPELINE_BIND_POINT_GRAPHICS. (https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/vkspec.html#VUID-vkCmdDrawIndexed-renderPass-02684)

I have investigated and the cause is fairly simple. The Dear ImGui rendering system has two paths: one for the main user-created window, in which, for Vulkan the user sets-up the render pass. The other path is the one used for any new window created when un-docking a window from the main window. In that path, ImGui has created its own render pass and keeps it as wd->RenderPass.
However, there is only one VkPipeline ( g_Pipeline ) created. That pipeline is created with the user-supplied render pass. And in general, there's no guarantee that the render pass created for the window is compatible with the user-supplied one.

The solution is to create a pipeline for the internally-created windows and use that pipeline for drawing such windows. The only difficulty is that the window/rendering context is not currently passed to ImGui_ImplVulkan_RenderDrawData.
I will probably start by adding an optional last argument passing the pipeline to be used and if not supplied, the current g_Pipeline will be used.

Standalone, minimal, complete and verifiable example:
I have debugged the issue. I can create a complete verifiable example in the context of the Vookoo framework
It's not exactly what you'd call a minimal example. Is that useful?

[ocornut]

Hello @FunMiles, I haven't been able to look at this in details but a thoughtful pull-request would be appreciated to fix the issue, if you understand it yourself.

[FunMiles]

HI @ocornut, I have created a pull-request. It refactors some shader-module creation code and adds one member to the externally visible ImGui_ImplVulkanH_Window structure and one arguments to ImGui_ImplVulkan_RenderDrawData with a default argument.
The resulting code should be backward compatible, only requiring to recompile because of the change to the size of the structure.

[ocornut]

All fixed by #3459, thank you!