fix: add VkSampler cache to prevent sampler exhaustion crash

Validation layers revealed 9965 VkSamplers allocated against a device
limit of 4000 — every VkTexture created its own sampler even when
configurations were identical. This exhausted NVIDIA's sampler pool
and caused intermittent SIGSEGV in vkCmdBeginRenderPass.

Add a thread-safe sampler cache in VkContext that deduplicates samplers
by FNV-1a hash of all 14 VkSamplerCreateInfo fields. All texture,
render target, renderer, water, and loading screen sampler creation
now goes through getOrCreateSampler(). Textures set ownsSampler_=false
so shared samplers aren't double-freed.

Also auto-disable anisotropy in the cache when the physical device
doesn't support the samplerAnisotropy feature, fixing the validation
error VUID-VkSamplerCreateInfo-anisotropyEnable-01070.

include/rendering/vk_context.hpp

@@ -8,6 +8,8 @@
 #include <vector>
 #include <functional>
 #include <cstdint>
+#include <unordered_map>
+#include <mutex>
 
 namespace wowee {
 namespace rendering {
@@ -119,6 +121,18 @@ public:
     VkImageView getDepthResolveImageView() const { return depthResolveImageView; }
     VkImageView getDepthImageView() const { return depthImageView; }
 
+    // Sampler cache: returns a shared VkSampler matching the given create info.
+    // Callers must NOT destroy the returned sampler — it is owned by VkContext.
+    // Automatically clamps anisotropy if the device doesn't support it.
+    VkSampler getOrCreateSampler(const VkSamplerCreateInfo& info);
+
+    // Whether the physical device supports sampler anisotropy.
+    bool isSamplerAnisotropySupported() const { return samplerAnisotropySupported_; }
+
+    // Global sampler cache accessor (set during VkContext::initialize, cleared on shutdown).
+    // Used by VkTexture and other code that only has a VkDevice handle.
+    static VkContext* globalInstance() { return sInstance_; }
+
     // UI texture upload: creates a Vulkan texture from RGBA data and returns
     // a VkDescriptorSet suitable for use as ImTextureID.
     // The caller does NOT need to free the result — resources are tracked and
@@ -239,6 +253,13 @@ private:
     };
     std::vector<UiTexture> uiTextures_;
 
+    // Sampler cache — deduplicates VkSamplers by configuration hash.
+    std::mutex samplerCacheMutex_;
+    std::unordered_map<uint64_t, VkSampler> samplerCache_;
+    bool samplerAnisotropySupported_ = false;
+
+    static VkContext* sInstance_;
+
 #ifndef NDEBUG
     bool enableValidation = true;
 #else

include/rendering/vk_render_target.hpp

@@ -73,6 +73,7 @@ private:
     bool hasDepth_ = false;
     VkSampleCountFlagBits msaaSamples_ = VK_SAMPLE_COUNT_1_BIT;
     VkSampler sampler_ = VK_NULL_HANDLE;
+    bool ownsSampler_ = true;
     VkRenderPass renderPass_ = VK_NULL_HANDLE;
     VkFramebuffer framebuffer_ = VK_NULL_HANDLE;
 };

include/rendering/vk_texture.hpp

@@ -72,6 +72,7 @@ private:
     AllocatedImage image_{};
     VkSampler sampler_ = VK_NULL_HANDLE;
     uint32_t mipLevels_ = 1;
+    bool ownsSampler_ = true; // false when sampler comes from VkContext cache
 };
 
 } // namespace rendering