Variable frame intervals when using VK_PRESENT_MODE_FIFO_KHR on adaptive‑sync displays

Variable frame intervals when using VK_PRESENT_MODE_FIFO_KHR on adaptive‑sync displays

The goal is to verify whether presenting images with VK_PRESENT_MODE_FIFO_KHR yields a stable frame interval on a monitor whose refresh rate can change dynamically (e.g., FreeSync, G‑Sync).

Because the Vulkan specification does not define exact presentation timestamps relative to the vertical blank when the display’s refresh rate varies, drivers may insert extra present intervals, duplicate the last image, or drop frames, leading to observable jitter. Validation layers currently do not warn about these timing variations, so the behavior must be inferred from instrumentation.

• Does VK_PRESENT_MODE_FIFO_KHR guarantee a constant CPU‑to‑GPU interval when the underlying display changes its refresh rate?
• Under what conditions do drivers choose to duplicate versus drop a frame when a present opportunity is missed?