2 files changed, 41 insertions, 7 deletions

diff --git a/src/video_core/engines/maxwell_3d.cpp b/src/video_core/engines/maxwell_3d.cpp
index ce536e29b..ba63b44b4 100644
--- a/src/video_core/engines/maxwell_3d.cpp
+++ b/src/video_core/engines/maxwell_3d.cpp
@@ -98,6 +98,8 @@ void Maxwell3D::InitializeRegisterDefaults() {
     regs.framebuffer_srgb = 1;
     regs.front_face = Maxwell3D::Regs::FrontFace::ClockWise;
 
+    shadow_state = regs;
+
     mme_inline[MAXWELL3D_REG_INDEX(draw.vertex_end_gl)] = true;
     mme_inline[MAXWELL3D_REG_INDEX(draw.vertex_begin_gl)] = true;
     mme_inline[MAXWELL3D_REG_INDEX(vertex_buffer.count)] = true;
@@ -160,8 +162,17 @@ void Maxwell3D::CallMethod(const GPU::MethodCall& method_call) {
     ASSERT_MSG(method < Regs::NUM_REGS,
                "Invalid Maxwell3D register, increase the size of the Regs structure");
 
-    if (regs.reg_array[method] != method_call.argument) {
-        regs.reg_array[method] = method_call.argument;
+    u32 arg = method_call.argument;
+    // Keep track of the register value in shadow_state when requested.
+    if (shadow_state.shadow_ram_control == Regs::ShadowRamControl::Track ||
+        shadow_state.shadow_ram_control == Regs::ShadowRamControl::TrackWithFilter) {
+        shadow_state.reg_array[method] = arg;
+    } else if (shadow_state.shadow_ram_control == Regs::ShadowRamControl::Replay) {
+        arg = shadow_state.reg_array[method];
+    }
+
+    if (regs.reg_array[method] != arg) {
+        regs.reg_array[method] = arg;
 
         for (const auto& table : dirty.tables) {
             dirty.flags[table[method]] = true;
@@ -169,12 +180,16 @@ void Maxwell3D::CallMethod(const GPU::MethodCall& method_call) {
     }
 
     switch (method) {
+    case MAXWELL3D_REG_INDEX(shadow_ram_control): {
+        shadow_state.shadow_ram_control = static_cast<Regs::ShadowRamControl>(method_call.argument);
+        break;
+    }
     case MAXWELL3D_REG_INDEX(macros.data): {
-        ProcessMacroUpload(method_call.argument);
+        ProcessMacroUpload(arg);
         break;
     }
     case MAXWELL3D_REG_INDEX(macros.bind): {
-        ProcessMacroBind(method_call.argument);
+        ProcessMacroBind(arg);
         break;
     }
     case MAXWELL3D_REG_INDEX(firmware[4]): {
@@ -250,7 +265,7 @@ void Maxwell3D::CallMethod(const GPU::MethodCall& method_call) {
     }
     case MAXWELL3D_REG_INDEX(data_upload): {
         const bool is_last_call = method_call.IsLastCall();
-        upload_state.ProcessData(method_call.argument, is_last_call);
+        upload_state.ProcessData(arg, is_last_call);
         if (is_last_call) {
             OnMemoryWrite();
         }
diff --git a/src/video_core/engines/maxwell_3d.h b/src/video_core/engines/maxwell_3d.h
index 8a9e9992e..d24c9f657 100644
--- a/src/video_core/engines/maxwell_3d.h
+++ b/src/video_core/engines/maxwell_3d.h
@@ -531,6 +531,17 @@ public:
             Fill = 0x1b02,
         };
 
+        enum class ShadowRamControl : u32 {
+            // write value to shadow ram
+            Track = 0,
+            // write value to shadow ram ( with validation ??? )
+            TrackWithFilter = 1,
+            // only write to real hw register
+            Passthrough = 2,
+            // write value from shadow ram to real hw register
+            Replay = 3,
+        };
+
         struct RenderTargetConfig {
             u32 address_high;
             u32 address_low;
@@ -674,7 +685,9 @@ public:
                     u32 bind;
                 } macros;
 
-                INSERT_UNION_PADDING_WORDS(0x17);
+                ShadowRamControl shadow_ram_control;
+
+                INSERT_UNION_PADDING_WORDS(0x16);
 
                 Upload::Registers upload;
                 struct {
@@ -1263,7 +1276,12 @@ public:
             };
             std::array<u32, NUM_REGS> reg_array;
         };
-    } regs{};
+    };
+
+    Regs regs{};
+
+    /// Store temporary hw register values, used by some calls to restore state after a operation
+    Regs shadow_state;
 
     static_assert(sizeof(Regs) == Regs::NUM_REGS * sizeof(u32), "Maxwell3D Regs has wrong size");
     static_assert(std::is_trivially_copyable_v<Regs>, "Maxwell3D Regs must be trivially copyable");
@@ -1458,6 +1476,7 @@ private:
                   "Field " #field_name " has invalid position")
 
 ASSERT_REG_POSITION(macros, 0x45);
+ASSERT_REG_POSITION(shadow_ram_control, 0x49);
 ASSERT_REG_POSITION(upload, 0x60);
 ASSERT_REG_POSITION(exec_upload, 0x6C);
 ASSERT_REG_POSITION(data_upload, 0x6D);