[vulkan] add native cubic filtering (#88)

Co-authored-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/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>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/video_core/host_shaders/convert_abgr8_srgb_to_d24s8.frag b/src/video_core/host_shaders/convert_abgr8_srgb_to_d24s8.frag
index a9bd21192d..2e464fffa6 100644
--- a/src/video_core/host_shaders/convert_abgr8_srgb_to_d24s8.frag
+++ b/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);