[buffer_cache] Add option to control GPU buffer readback (#4126)

Added an option to control the GPU buffer readback, as it causes issues if the hardware cannot keep up with the additional workload.

Some games require this to render certain effects properly.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4126

src/common/settings.h

@@ -573,6 +573,13 @@ struct Values {
         false,
 #endif
         "rescale_hack", Category::RendererHacks};
+    SwitchableSetting<bool> enable_gpu_buffer_readback{linkage,
+                                                       false,
+                                                       "enable_gpu_buffer_readback",
+                                                       Category::RendererAdvanced,
+                                                       Specialization::Default,
+                                                       true,
+                                                       true};
 
     SwitchableSetting<bool> use_asynchronous_shaders{linkage, false, "use_asynchronous_shaders",
                                                      Category::RendererHacks};

src/qt_common/config/shared_translation.cpp

@@ -229,6 +229,8 @@ std::unique_ptr<TranslationMap> InitializeTranslations(QObject* parent) {
     INSERT(Settings, dma_accuracy, tr("DMA Accuracy:"),
            tr("Controls the DMA precision accuracy. Safe precision fixes issues in some games but "
               "may degrade performance."));
+    INSERT(Settings, enable_gpu_buffer_readback, tr("Enable GPU buffer readback"),
+           tr("Preserves GPU-modified buffer data by reading it back before uploads.\nSome games require this to render certain effects properly.\nMay cause issues if the hardware cannot handle the additional workload."));
     INSERT(Settings, use_asynchronous_shaders, tr("Enable asynchronous shader compilation"),
            tr("May reduce shader stutter."));
     INSERT(Settings, fast_gpu_time, tr("Fast GPU Time"),

src/video_core/buffer_cache/buffer_cache.h

@@ -1634,15 +1634,17 @@ bool BufferCache<P>::SynchronizeBuffer(Buffer& buffer, DAddr device_addr, u32 si
     if (total_size_bytes == 0) {
         return true;
     }
-    u64 min_offset = (std::numeric_limits<u64>::max)();
-    u64 max_offset = 0;
-    for (const auto& copy : upload_copies) {
-        min_offset = (std::min)(min_offset, copy.dst_offset);
-        max_offset = (std::max)(max_offset, copy.dst_offset + copy.size);
-    }
-    const DAddr sync_addr = buffer.CpuAddr() + min_offset;
-    const u64 sync_size = max_offset - min_offset;
-    DownloadBufferMemory(buffer, sync_addr, sync_size);
+    if (Settings::values.enable_gpu_buffer_readback.GetValue()) {
+        u64 min_offset = (std::numeric_limits<u64>::max)();
+        u64 max_offset = 0;
+        for (const auto& copy : upload_copies) {
+            min_offset = (std::min)(min_offset, copy.dst_offset);
+            max_offset = (std::max)(max_offset, copy.dst_offset + copy.size);
+        }
+        const DAddr sync_addr = buffer.CpuAddr() + min_offset;
+        const u64 sync_size = max_offset - min_offset;
+        DownloadBufferMemory(buffer, sync_addr, sync_size);
+    }
     const std::span<BufferCopy> copies_span(upload_copies.data(), upload_copies.size());
     UploadMemory(buffer, total_size_bytes, largest_copy, copies_span);
     any_buffer_uploaded = true;