From 583a9fd32032703853bb4343bc91a15fdb714b40 Mon Sep 17 00:00:00 2001
From: CamilleLaVey <camillelavey99@gmail.com>
Date: Thu, 4 Dec 2025 02:44:06 -0400
Subject: [PATCH] [maxwell, vk] Allocate data transfer from Maxwell to VK using
 Sample Locations as channel for MSAA

---
 .../renderer_vulkan/vk_graphics_pipeline.cpp  | 11 +++++--
 .../renderer_vulkan/vk_rasterizer.cpp         | 33 +++++++++++++++++--
 2 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/src/video_core/renderer_vulkan/vk_graphics_pipeline.cpp b/src/video_core/renderer_vulkan/vk_graphics_pipeline.cpp
index d89a992281..170fba1897 100644
--- a/src/video_core/renderer_vulkan/vk_graphics_pipeline.cpp
+++ b/src/video_core/renderer_vulkan/vk_graphics_pipeline.cpp
@@ -862,8 +862,14 @@ void GraphicsPipeline::MakePipeline(VkRenderPass render_pass) {
     const bool alpha_to_one_supported = device.SupportsAlphaToOne();
     const auto msaa_mode = key.state.msaa_mode.Value();
     const VkSampleCountFlagBits vk_samples = MaxwellToVK::MsaaMode(msaa_mode);
-    const bool supports_sample_locations =
-        device.IsExtSampleLocationsSupported() && device.SupportsSampleLocationsFor(vk_samples);
+    const auto [grid_width, grid_height] = VideoCommon::SampleLocationGridSize(msaa_mode);
+    const auto& sample_location_props = device.SampleLocationProperties();
+    const bool grid_within_limits = grid_width <= sample_location_props.maxSampleLocationGridSize.width &&
+                                    grid_height <= sample_location_props.maxSampleLocationGridSize.height;
+    const bool supports_sample_locations = device.IsExtSampleLocationsSupported() &&
+                                           device.SupportsSampleLocationsFor(vk_samples) &&
+                                           sample_location_props.variableSampleLocations == VK_TRUE &&
+                                           grid_within_limits;
 
     VkPipelineMultisampleStateCreateInfo multisample_ci{
         .sType = VK_STRUCTURE_TYPE_PIPELINE_MULTISAMPLE_STATE_CREATE_INFO,
@@ -888,7 +894,6 @@ void GraphicsPipeline::MakePipeline(VkRenderPass render_pass) {
     if (supports_sample_locations) {
         sample_locations_chain.emplace();
         auto& chain = *sample_locations_chain;
-        const auto [grid_width, grid_height] = VideoCommon::SampleLocationGridSize(msaa_mode);
         const u32 samples_per_pixel = static_cast<u32>(VideoCommon::NumSamples(msaa_mode));
         const u32 sample_locations_count = grid_width * grid_height * samples_per_pixel;
         chain.locations.fill(VkSampleLocationEXT{0.5f, 0.5f});
diff --git a/src/video_core/renderer_vulkan/vk_rasterizer.cpp b/src/video_core/renderer_vulkan/vk_rasterizer.cpp
index 5cc4a80306..51afa06327 100644
--- a/src/video_core/renderer_vulkan/vk_rasterizer.cpp
+++ b/src/video_core/renderer_vulkan/vk_rasterizer.cpp
@@ -6,6 +6,7 @@
 
 #include <algorithm>
 #include <array>
+#include <cmath>
 #include <memory>
 #include <mutex>
 
@@ -1713,9 +1714,22 @@ void RasterizerVulkan::UpdateSampleLocations(Maxwell& regs) {
         return;
     }
 
+    const auto& sample_props = device.SampleLocationProperties();
+    if (sample_props.variableSampleLocations == VK_FALSE) {
+        return;
+    }
+
     const auto [grid_width_u32, grid_height_u32] = VideoCommon::SampleLocationGridSize(msaa_mode);
     const u32 grid_width = grid_width_u32;
     const u32 grid_height = grid_height_u32;
+    if (grid_width > sample_props.maxSampleLocationGridSize.width ||
+        grid_height > sample_props.maxSampleLocationGridSize.height) {
+        LOG_WARNING(Render_Vulkan,
+                    "Sample location grid {}x{} exceeds device limit {}x{}, falling back to fixed pattern",
+                    grid_width, grid_height, sample_props.maxSampleLocationGridSize.width,
+                    sample_props.maxSampleLocationGridSize.height);
+        return;
+    }
     const u32 samples_per_pixel = static_cast<u32>(VideoCommon::NumSamples(msaa_mode));
     const u32 grid_cells = grid_width * grid_height;
     const u32 sample_locations_count = grid_cells * samples_per_pixel;
@@ -1723,15 +1737,30 @@ void RasterizerVulkan::UpdateSampleLocations(Maxwell& regs) {
 
     const auto raw_locations = DecodeSampleLocationRegisters(regs);
     std::array<VkSampleLocationEXT, VideoCommon::MaxSampleLocationSlots> resolved{};
+    const float coord_min = sample_props.sampleLocationCoordinateRange[0];
+    const float coord_max = sample_props.sampleLocationCoordinateRange[1];
+    const float host_unit = sample_props.sampleLocationSubPixelBits > 0
+                                ? 1.0f / static_cast<float>(1u << sample_props.sampleLocationSubPixelBits)
+                                : 0.0f;
+    const auto sanitize_coord = [&](float value) {
+        float clamped = std::clamp(value, coord_min, coord_max);
+        if (host_unit > 0.0f) {
+            clamped = coord_min + std::round((clamped - coord_min) / host_unit) * host_unit;
+            clamped = std::clamp(clamped, coord_min, coord_max);
+        }
+        return clamped;
+    };
     for (u32 cell = 0; cell < grid_cells; ++cell) {
         const u32 slot_base = cell * samples_per_pixel;
         const u32 cell_x = cell % grid_width;
         const u32 cell_y = cell / grid_width;
         for (u32 sample = 0; sample < samples_per_pixel; ++sample) {
             const VkSampleLocationEXT raw = raw_locations[slot_base + sample];
+            const float sample_x = static_cast<float>(cell_x) + raw.x;
+            const float sample_y = static_cast<float>(cell_y) + raw.y;
             resolved[slot_base + sample] = VkSampleLocationEXT{
-                .x = static_cast<float>(cell_x) + raw.x,
-                .y = static_cast<float>(cell_y) + raw.y,
+                .x = sanitize_coord(sample_x),
+                .y = sanitize_coord(sample_y),
             };
         }
     }