[vulkan] add native cubic filtering (#88)

Co-authored-by: crueter <crueter@eden-emu.dev>
Reviewed-on: #88

This implements the use of VK_FILTER_CUBIC_EXT as a replacement for the software-based bicubic window adapting filter, used primarily for texture sampling in upscaled or downscaled surfaces such as UI, transparency effects, and screen-space elements in Unreal Engine 4 titles.

The Vulkan cubic filter is now conditionally enabled if the following are satisfied:

The device supports VK_EXT_filter_cubic

The format used supports VK_FORMAT_FEATURE_SAMPLED_IMAGE_FILTER_CUBIC_BIT_EXT

This change improves visual quality while reducing GPU workload by offloading cubic filtering to the driver instead of running custom sampling code in shaders. On supported hardware (e.g. desktop GPUs or high-end Adreno/AMD devices), it results in smoother transitions, improved transparency sampling, and better fidelity with lower shader complexity.

Fallback to the original software bicubic logic remains in place for devices lacking the extension or format capability.

Tested on several UE4 titles and confirmed to preserve or enhance visual output, especially in alpha-blended and UI-heavy scenes.
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/video_core/host_shaders/convert_abgr8_srgb_to_d24s8.frag

@@ -5,9 +5,10 @@
 
 layout(binding = 0) uniform sampler2D color_texture;
 
-// More accurate sRGB to linear conversion
+// Even more accurate sRGB to linear conversion
+// https://entropymine.com/imageworsener/srgbformula/
 float srgbToLinear(float srgb) {
-    if (srgb <= 0.04045) {
+    if (srgb <= 0.0404482362771082f) { //assumes it's >= 0
         return srgb / 12.92;
     } else {
         return pow((srgb + 0.055) / 1.055, 2.4);

src/video_core/renderer_vulkan/present/filters.cpp

@@ -46,8 +46,12 @@ std::unique_ptr<WindowAdaptPass> MakeBilinear(const Device& device, VkFormat fra
 }
 
 std::unique_ptr<WindowAdaptPass> MakeBicubic(const Device& device, VkFormat frame_format) {
+    // No need for handrolled shader -- if the VK impl can do it for us ;)
+    if (device.IsExtFilterCubicSupported())
+        return std::make_unique<WindowAdaptPass>(device, frame_format, CreateCubicSampler(device),
+                                                 BuildShader(device, VULKAN_PRESENT_FRAG_SPV));
     return std::make_unique<WindowAdaptPass>(device, frame_format, CreateBilinearSampler(device),
-                                             BuildShader(device, PRESENT_BICUBIC_FRAG_SPV));
+                                                BuildShader(device, PRESENT_BICUBIC_FRAG_SPV));
 }
 
 std::unique_ptr<WindowAdaptPass> MakeGaussian(const Device& device, VkFormat frame_format) {

src/video_core/renderer_vulkan/present/util.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2024 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -621,6 +624,31 @@ vk::Sampler CreateNearestNeighborSampler(const Device& device) {
     return device.GetLogical().CreateSampler(ci_nn);
 }
 
+vk::Sampler CreateCubicSampler(const Device& device) {
+    const VkSamplerCreateInfo ci_nn{
+        .sType = VK_STRUCTURE_TYPE_SAMPLER_CREATE_INFO,
+        .pNext = nullptr,
+        .flags = 0,
+        .magFilter = VK_FILTER_CUBIC_EXT,
+        .minFilter = VK_FILTER_CUBIC_EXT,
+        .mipmapMode = VK_SAMPLER_MIPMAP_MODE_NEAREST,
+        .addressModeU = VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_BORDER,
+        .addressModeV = VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_BORDER,
+        .addressModeW = VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_BORDER,
+        .mipLodBias = 0.0f,
+        .anisotropyEnable = VK_FALSE,
+        .maxAnisotropy = 0.0f,
+        .compareEnable = VK_FALSE,
+        .compareOp = VK_COMPARE_OP_NEVER,
+        .minLod = 0.0f,
+        .maxLod = 0.0f,
+        .borderColor = VK_BORDER_COLOR_FLOAT_OPAQUE_BLACK,
+        .unnormalizedCoordinates = VK_FALSE,
+    };
+
+    return device.GetLogical().CreateSampler(ci_nn);
+}
+
 void ClearColorImage(vk::CommandBuffer& cmdbuf, VkImage image) {
     static constexpr std::array<VkImageSubresourceRange, 1> subresources{{{
         .aspectMask = VK_IMAGE_ASPECT_COLOR_BIT,

src/video_core/renderer_vulkan/present/util.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2024 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -54,6 +57,7 @@ VkWriteDescriptorSet CreateWriteDescriptorSet(std::vector<VkDescriptorImageInfo>
                                               VkDescriptorSet set, u32 binding);
 vk::Sampler CreateBilinearSampler(const Device& device);
 vk::Sampler CreateNearestNeighborSampler(const Device& device);
+vk::Sampler CreateCubicSampler(const Device& device);
 
 void BeginRenderPass(vk::CommandBuffer& cmdbuf, VkRenderPass render_pass, VkFramebuffer framebuffer,
                      VkExtent2D extent);

src/video_core/vulkan_common/vulkan_device.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -85,7 +88,8 @@ VK_DEFINE_HANDLE(VmaAllocator)
     EXTENSION(NV, GEOMETRY_SHADER_PASSTHROUGH, geometry_shader_passthrough)                        \
     EXTENSION(NV, VIEWPORT_ARRAY2, viewport_array2)                                                \
     EXTENSION(NV, VIEWPORT_SWIZZLE, viewport_swizzle)                                              \
-    EXTENSION(EXT, DESCRIPTOR_INDEXING, descriptor_indexing)
+    EXTENSION(EXT, DESCRIPTOR_INDEXING, descriptor_indexing)                                       \
+    EXTENSION(EXT, FILTER_CUBIC, filter_cubic)
 
 // Define extensions which must be supported.
 #define FOR_EACH_VK_MANDATORY_EXTENSION(EXTENSION_NAME)                                            \
@@ -549,6 +553,11 @@ public:
         return dynamic_state3_enables;
     }
 
+    /// Returns true if the device supports VK_EXT_filter_cubic
+    bool IsExtFilterCubicSupported() const {
+        return extensions.filter_cubic;
+    }
+
     /// Returns true if the device supports VK_EXT_line_rasterization.
     bool IsExtLineRasterizationSupported() const {
         return extensions.line_rasterization;