2 files changed, 140 insertions, 0 deletions
diff --git a/shaders/texture-unit-cache.cpp b/shaders/texture-unit-cache.cpp
new file mode 100644
index 00000000..918ee56c
--- /dev/null
+++ b/shaders/texture-unit-cache.cpp
@@ -0,0 +1,105 @@
+#include "texture-unit-cache.hpp"
+
+#include "compat/assert.hpp"
+#include <Magnum/GL/Texture.h>
+
+namespace floormat {
+
+struct texture_unit_cache::unit_data final
+{
+    GL::AbstractTexture* ptr;
+    size_t lru_val;
+};
+
+int32_t texture_unit_cache::bind(GL::AbstractTexture* tex)
+{
+    fm_debug_assert(tex != nullptr && tex != (GL::AbstractTexture*)-1);
+
+    constexpr auto invalid = (size_t)-1;
+    auto unbound_id = invalid;
+
+    for (auto i = 0uz; i < unit_count; i++)
+    {
+        auto& unit = units[i];
+        auto* ptr = unit.ptr;
+        if (!ptr)
+            unbound_id = i;
+        else if (ptr == tex)
+        {
+            unit.lru_val = ++lru_counter;
+            ++cache_hit_count;
+            return (int32_t)i;
+        }
+    }
+
+    if (unbound_id != invalid)
+    {
+        units[unbound_id] = {tex, ++lru_counter};
+        tex->bind((Int)unbound_id);
+        ++cache_hit_count;
+        auto label = tex->label();
+        Debug{Debug::Flag::NoSpace} << "binding '" << tex->label() << "' to " << unbound_id;
+        return (int32_t)unbound_id;
+    }
+    else
+    {
+        auto min_lru = invalid, min_index = invalid;
+        for (auto i = 0uz; i < unit_count; i++)
+        {
+            auto& unit = units[i];
+            if (unit.lru_val < min_lru)
+            {
+                min_lru = unit.lru_val;
+                min_index = i;
+            }
+        }
+        fm_assert(min_index != invalid);
+        ++rebind_count;
+        units[min_index] = {tex, ++lru_counter};
+        tex->bind((Int)min_index);
+        Debug{Debug::Flag::NoSpace} << "binding '" << tex->label() << "' to " << min_index;
+        return (int32_t)min_index;
+    }
+}
+
+texture_unit_cache::texture_unit_cache() :
+    unit_count{get_unit_count()},
+    units{ValueInit, unit_count}
+{
+}
+
+void texture_unit_cache::invalidate()
+{
+    units = {};
+    lru_counter = 0;
+    rebind_count = 0;
+}
+
+void texture_unit_cache::lock(floormat::size_t i, GL::AbstractTexture* tex)
+{
+    fm_assert(i < unit_count);
+    units[i] = { .ptr = tex, .lru_val = (uint64_t)i, };
+}
+
+void texture_unit_cache::unlock(size_t i, bool immediately)
+{
+    fm_assert(i < unit_count);
+    if (units[i].ptr == (GL::AbstractTexture*)-1)
+        immediately = true;
+    units[i] = { .ptr = units[i].ptr, .lru_val = immediately ? 0 : ++lru_counter };
+}
+
+size_t texture_unit_cache::get_unit_count()
+{
+    static auto ret = [] {
+        GLint value = 0;
+        glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS, &value);
+        fm_assert(value >= /*GL 3.3*/ 16);
+        return value;
+    }();
+    return (size_t)ret;
+}
+
+int32_t texture_unit_cache::bind(GL::AbstractTexture& x) { return bind(&x); }
+
+} // namespace floormat
diff --git a/shaders/texture-unit-cache.hpp b/shaders/texture-unit-cache.hpp
new file mode 100644
index 00000000..2647ea8c
--- /dev/null
+++ b/shaders/texture-unit-cache.hpp
@@ -0,0 +1,35 @@
+#pragma once
+#include "compat/defs.hpp"
+#include <Corrade/Containers/Array.h>
+
+namespace Magnum::GL { class AbstractTexture; }
+
+namespace floormat {
+
+struct texture_unit_cache final
+{
+    fm_DECLARE_DELETED_COPY_ASSIGNMENT(texture_unit_cache);
+    fm_DECLARE_DEFAULT_MOVE_ASSIGNMENT_(texture_unit_cache);
+
+    texture_unit_cache();
+
+    [[nodiscard]] int32_t bind(GL::AbstractTexture* ptr);
+    [[nodiscard]] int32_t bind(GL::AbstractTexture& x);
+    void invalidate();
+    void lock(size_t i, GL::AbstractTexture* = (GL::AbstractTexture*)-1);
+    void lock(size_t i, GL::AbstractTexture& tex) { lock(i, &tex); }
+    void unlock(size_t i, bool immediately = true);
+
+    size_t reuse_count() const { return cache_hit_count; }
+    size_t bind_count() const { return rebind_count; }
+    void reset_stats() { rebind_count = cache_hit_count = 0; }
+
+private:
+    static size_t get_unit_count();
+    struct unit_data;
+
+    size_t unit_count, lru_counter = 0, rebind_count = 0, cache_hit_count = 0;
+    Array<unit_data> units;
+};
+
+} // namespace floormat