If we assign VkSwapchainCreateInfoKHR.presentMode = VK_PRESENT_MODE_IMMEDIATE_KHR; as I understand, we have a single buffer and the image is being presented to the surface immediately,
but at the same time SwapChainDetails.surfaceCapabilities.minImageCount = 2; on my GTX 1070.
Does minImageCount mean that minimum number of buffers should be 2 ?
How does it even work ?
How do Swapchain minImageCount and VK_PRESENT_MODE_IMMEDIATE_KHR relate to each other?
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1 Answers
They don't relate to each other at all. How many buffers you have has nothing to do with how they get displayed.
Immediate presentation means that, when you present an image, it is displayed immediately. As stated in the standard:
the presentation engine does not wait for a vertical blanking period to update the current image
If the presentation engine only allowed you one swapchain image, then this would mean that the acquire would have to wait until the image is finished being shown. This would make immediate presentation pointless.
Now, you might think that acquiring such an image ought to happen immediately. But that would mean that you could render to the image while the presentation engine is still reading from it, causing potential corruption. But that's not what immediate presentation is for. Immediate presentation changes nothing about the ownership dynamics between the presentation engine and user code; it only changes the timing of how swapchain images are presented.
The ability to write to an image that is actually being presented is governed by the "shared" present modes (VK_PRESENT_MODE_SHARED_DEMAND_REFRESH_KHR and VK_PRESENT_MODE_SHARED_CONTINUOUS_REFRESH_KHR).
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