[bug report] vkCmdSetCullModeEXT(...VK_CULL_MODE_NONE) not worked as expected caused by dirty flag

[awkr]

Hi everyone. I have two pipelines, which are created from the same VkPipelineLayout:

• pipeline T:
  • primitive topology is VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST
  • has two dynamic states: VK_DYNAMIC_STATE_POLYGON_MODE_EXT, VK_DYNAMIC_STATE_CULL_MODE_EXT
• pipeline G:
  • primitive topology is VK_PRIMITIVE_TOPOLOGY_LINE_LIST
  • has no dynamic state

Then I rendered two entities, just TWO:

• entity Triangle:
  • a triangle with indices
• entity Grid:
  • a line grid with no indices, just vertices

For simplicity, my code is like:

begin render pass
  // draw entity Grid
  bind pipeline G
  draw
  // draw entity Triangle
  bind pipeline T
  cmd set polygon mode to LINE <-- it works
  cmd set cull mode to NONE <-- it does not work, triangle is invisible
  draw indexed
end render pass

But if I change the code execution order to:

begin render pass
  // draw entity Triangle
  bind pipeline T
  cmd set polygon mode to LINE <-- it works
  cmd set cull mode to NONE <-- it also works
  draw indexed
  // draw entity Grid
  bind pipeline G
  draw
end render pass

I also tried:

• Making pipeline G have dynamic state VK_DYNAMIC_STATE_CULL_MODE_EXT, and set it when drawing, it also works in the first code snippet, but it is not what I want.
• Rendering more than two entities, it works too.

I don't know why, can you guys figure me out? Many thanks~

Context:

• macOS 15.5 (24F74)
• MoltenVK version 1.2.11, supporting Vulkan version 1.2.296.
• app using Vulkan API: VK_API_VERSION_1_2
• volk version 1.4.318
• swapchain image count: 3
• in flight frame count: 2
• In device creation:
  • enabled extensions: VK_EXT_extended_dynamic_state and VK_EXT_extended_dynamic_state3
  • pNext chain(part) of VkDeviceCreateInfo is :

  VkPhysicalDeviceExtendedDynamicStateFeaturesEXT dynamic_state_features{};
  dynamic_state_features.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_EXTENDED_DYNAMIC_STATE_FEATURES_EXT;
  dynamic_state_features.extendedDynamicState = VK_TRUE; // Enable extended dynamic state for cull mode
  
  VkPhysicalDeviceExtendedDynamicState3FeaturesEXT extended_dynamic_state3_features_ext{};
  extended_dynamic_state3_features_ext.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_EXTENDED_DYNAMIC_STATE_3_FEATURES_EXT;
  extended_dynamic_state3_features_ext.extendedDynamicState3PolygonMode = VK_TRUE;
  extended_dynamic_state3_features_ext.pNext = &dynamic_state_features;
  

[awkr]

Hi, I tried to build MoltenVK from source code and added some debugging logs. It turned out that cullMode passed to MVKRenderingCommandEncoderState::setCullMode was not used in MVKGraphicsPipeline::encode, reset by _rasterInfo.cullMode, here are some logs:

Since cull mode is dynamic, and dynamic states should always be provided, so I simply comment out cmdEncRS.setCullMode(_rasterInfo.cullMode, false);, vkCmdSetCullModeExt works now.

Update:
After some digging, the logic of this bug is:

1. The initial value of _mtlCullMode is: MTLCullMode _mtlCullMode[StateScope::Count] = { MTLCullModeNone, MTLCullModeNone };
2. On the app side, call vkCmdSetCullModeEXT(command_buffer, VK_CULL_MODE_NONE);
3. Because the incoming value equals the initial value, the dirty flag was not set.