engine/rr: preset F's exposure in one pass with 64-bit atomics

exposure_f.comp ran NGX's auto exposure in two passes: the 16x16 blocks wrote
their fixed-point luma sums, then a single workgroup added them after a
barrier and finished (11 us of a 25 us stage). PASS 2 does what NVIDIA's
kernel does: each block adds its sum to a 64-bit total with an atomic add
and counts itself in with an acquire-release add; the last block reads the
total, finishes and leaves both words zero for the next frame. The total is
an integer, the same in any order, so the exposure image and the values are
the two passes' bit for bit. compile_rr2.py builds exposure_f2.spv next to
the two passes' shaders (the block sum and the finish are shared functions
now; their arithmetic is unchanged).

64-bit buffer atomics are a device feature (shaderBufferInt64Atomics), so
RModel takes whether the device has it enabled (default no) and preset F
uses the one pass only then and only with a model that has exposure_f2.spv;
otherwise the two passes as before. vkd3d-proton creates its device with
every feature the GPU reports except a list it turns off, which does not
include this one (it backs D3D12's 64-bit atomics with it); the shim reads
the device's features through the interop interface (GetDeviceFeatures) and
logs the result. d4r-rr enables every feature the GPU has, and
D4R_RR_TEST_NO_INT64_ATOMICS=1 turns this one off to run the two passes.
Ray Reconstruction never runs on the native Vulkan frontend's device.

Every image of every frame byte-identical to the previous build (1280x720
-> 1440p, 1114x626 -> 1080p, 960x540 -> 1080p, the stress inputs, with
D4R_RR_TEST_ROBUST2=1, at levels 0 and 3, with D4R_RR2_SPLIT=1), and so is
the two-pass fallback of the new build; presets D and E unchanged. Controls:
the last block finishing with twice the total changes 64 of the 90 images of
the 1280x720 sequence (and nothing under the fallback), finishing without
its own block's sum 58 of 90.

RX 9070 XT, d4r-rr 720p -> 1440p, interleaved: exposure 25.2 -> 14.9 us,
frame 3.536 -> 3.526 ms (the fallback 25.1 us).

Signed-off-by: itchyfeetleech <[email protected]>

engine/runtime.h

@@ -273,7 +273,10 @@ struct RFrameSettings {
 };
 class RModel {
 public:
-    RModel(VkPhysicalDevice physical, VkDevice device, const std::string& directory, VkPipelineCache cache = VK_NULL_HANDLE);
+    // int64Atomics: the device has shaderBufferInt64Atomics enabled; preset F then measures the exposure in one pass
+    // (engine/rr/exposure_f.comp PASS 2) instead of two
+    RModel(VkPhysicalDevice physical, VkDevice device, const std::string& directory, VkPipelineCache cache = VK_NULL_HANDLE,
+           bool int64Atomics = false);
     ~RModel();
     RModel(const RModel&) = delete;
     RModel& operator=(const RModel&) = delete;