From b461a3b64df7d172aaa4bd8382ebc2a93e74ebf5 Mon Sep 17 00:00:00 2001
From: Alex Shvartzkop <dudesuchamazing@gmail.com>
Date: Tue, 24 Oct 2023 03:36:51 +0300
Subject: [PATCH] OpenGL: Improve logic when bitmap cache memory is exhausted.

Don't remove the front entry, as it will likely be needed for the next bitmap.
Instead, implement neuristics based on access times.

(cherry picked from commit 71d0c7f6af14cb09667dd893060486b188a401e3)
---
 common/gal/opengl/opengl_gal.cpp | 60 +++++++++++++++++++++++---------
 1 file changed, 44 insertions(+), 16 deletions(-)

diff --git a/common/gal/opengl/opengl_gal.cpp b/common/gal/opengl/opengl_gal.cpp
index be69ef8075..c848814ec5 100644
--- a/common/gal/opengl/opengl_gal.cpp
+++ b/common/gal/opengl/opengl_gal.cpp
@@ -94,9 +94,10 @@ public:
 private:
     struct CACHED_BITMAP
     {
-        GLuint id;
-        int    w, h;
-        size_t size;
+        GLuint        id;
+        int           w, h;
+        size_t        size;
+        long long int accessTime;
     };
 
     GLuint cacheBitmap( const BITMAP_BASE* aBitmap );
@@ -105,9 +106,9 @@ private:
     const size_t m_cacheMaxSize     = 256 * 1024 * 1024;
 
     std::map<const KIID, CACHED_BITMAP> m_bitmaps;
-    std::list<KIID> m_cacheLru;
-    size_t m_cacheSize;
-    std::list<GLuint> m_freedTextureIds;
+    std::list<KIID>                     m_cacheLru;
+    size_t                              m_cacheSize;
+    std::list<GLuint>                   m_freedTextureIds;
 };
 
 }; // namespace KIGFX
@@ -130,6 +131,7 @@ GLuint GL_BITMAP_CACHE::RequestBitmap( const BITMAP_BASE* aBitmap )
         // A bitmap is found in cache bitmap. Ensure the associated texture is still valid.
         if( glIsTexture( it->second.id ) )
         {
+            it->second.accessTime = wxGetUTCTimeMillis().GetValue();
             return it->second.id;
         }
         else
@@ -243,26 +245,52 @@ GLuint GL_BITMAP_CACHE::cacheBitmap( const BITMAP_BASE* aBitmap )
     glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
     glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
 
+    long long currentTime = wxGetUTCTimeMillis().GetValue();
+
     bmp.id = textureID;
+    bmp.accessTime = currentTime;
 
 #ifndef DISABLE_BITMAP_CACHE
-    m_cacheLru.emplace_back( aBitmap->GetImageID() );
-    m_cacheSize += bmp.size;
-    m_bitmaps.emplace( aBitmap->GetImageID(), std::move( bmp ) );
-
-    if( m_cacheLru.size() > m_cacheMaxElements
-        || m_cacheSize > m_cacheMaxSize )
+    if( m_cacheLru.size() + 1 > m_cacheMaxElements || m_cacheSize + bmp.size > m_cacheMaxSize )
     {
-        KIID last = m_cacheLru.front();
-        CACHED_BITMAP& cachedBitmap = m_bitmaps[last];
+        KIID toRemove( 0 );
+        auto toRemoveLru = m_cacheLru.end();
+
+        // Remove entries accessed > 1s ago first
+        for( const auto& [kiid, bmp] : m_bitmaps )
+        {
+            const int cacheTimeoutMillis = 1000L;
+
+            if( currentTime - bmp.accessTime > cacheTimeoutMillis )
+            {
+                toRemove = kiid;
+                toRemoveLru = std::find( m_cacheLru.begin(), m_cacheLru.end(), toRemove );
+                break;
+            }
+        }
+
+        // Otherwise, remove the latest entry (it's less likely to be needed soon)
+        if( toRemove == niluuid )
+        {
+            toRemoveLru = m_cacheLru.end();
+            toRemoveLru--;
+
+            toRemove = *toRemoveLru;
+        }
+
+        CACHED_BITMAP& cachedBitmap = m_bitmaps[toRemove];
 
         m_cacheSize -= cachedBitmap.size;
         glDeleteTextures( 1, &cachedBitmap.id );
         m_freedTextureIds.emplace_back( cachedBitmap.id );
 
-        m_bitmaps.erase( last );
-        m_cacheLru.pop_front();
+        m_bitmaps.erase( toRemove );
+        m_cacheLru.erase( toRemoveLru );
     }
+
+    m_cacheLru.emplace_back( aBitmap->GetImageID() );
+    m_cacheSize += bmp.size;
+    m_bitmaps.emplace( aBitmap->GetImageID(), std::move( bmp ) );
 #endif
 
     return textureID;