fix that bug where NSMB's backgrounds lagged one frame behind

src/GPU.cpp

@@ -692,6 +692,12 @@ void StartScanline(u32 line)
         // (TODO, eventually: emulate it properly)
         NDS::CheckDMAs(0, 0x04);
 
+        if (line == 0)
+        {
+            GPU2D_A->VBlankEnd();
+            GPU2D_B->VBlankEnd();
+        }
+
         // draw
         GPU2D_A->DrawScanline(line);
         GPU2D_B->DrawScanline(line);

src/GPU2D.cpp

@@ -426,12 +426,16 @@ void GPU2D::DrawScanline(u32 line)
 
 void GPU2D::VBlank()
 {
+    CaptureCnt &= ~(1<<31);
+}
+
+void GPU2D::VBlankEnd()
+{
+    // TODO: find out the exact time this happens
     BGXRefInternal[0] = BGXRef[0];
     BGXRefInternal[1] = BGXRef[1];
     BGYRefInternal[0] = BGYRef[0];
     BGYRefInternal[1] = BGYRef[1];
-
-    CaptureCnt &= ~(1<<31);
 }
 
 

src/GPU2D.h

@@ -38,6 +38,7 @@ public:
 
     void DrawScanline(u32 line);
     void VBlank();
+    void VBlankEnd();
 
     void BGExtPalDirty(u32 base);
     void OBJExtPalDirty();