From 3c006fd36154e48325c3cf862ed3287b265924c1 Mon Sep 17 00:00:00 2001
From: Arisotura <thetotalworm@gmail.com>
Date: Wed, 24 Jul 2019 02:46:30 +0200
Subject: [PATCH] GPU2D: fill gaps in BG modes * mode6 actually works on the
 sub GPU, albeit limited to 1/4 the full bitmap size due to having only 128K
 of VRAM * mode7 draws BG0, BG1 and sprites. no BG2/BG3.

---
 src/GPU2D.cpp | 38 ++++++++++++++++++++++++++++++--------
 src/GPU2D.h   |  1 +
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/src/GPU2D.cpp b/src/GPU2D.cpp
index 9d7ab8f3..4bba2354 100644
--- a/src/GPU2D.cpp
+++ b/src/GPU2D.cpp
@@ -1316,12 +1316,6 @@ void GPU2D::DrawScanlineBGMode(u32 line)
 
 void GPU2D::DrawScanlineBGMode6(u32 line)
 {
-    if (Num)
-    {
-        printf("GPU2D: MODE6 ON SUB GPU???\n");
-        return;
-    }
-
     for (int i = 3; i >= 0; i--)
     {
         if ((BGCnt[2] & 0x3) == i)
@@ -1335,7 +1329,7 @@ void GPU2D::DrawScanlineBGMode6(u32 line)
         {
             if (DispCnt & 0x0100)
             {
-                if (DispCnt & 0x8)
+                if ((!Num) && (DispCnt & 0x8))
                     DrawBG_3D();
             }
         }
@@ -1344,6 +1338,34 @@ void GPU2D::DrawScanlineBGMode6(u32 line)
     }
 }
 
+void GPU2D::DrawScanlineBGMode7(u32 line)
+{
+    // mode 7 only has text-mode BG0 and BG1
+
+    for (int i = 3; i >= 0; i--)
+    {
+        if ((BGCnt[1] & 0x3) == i)
+        {
+            if (DispCnt & 0x0200)
+            {
+                DrawBG_Text(line, 1);
+            }
+        }
+        if ((BGCnt[0] & 0x3) == i)
+        {
+            if (DispCnt & 0x0100)
+            {
+                if ((!Num) && (DispCnt & 0x8))
+                    DrawBG_3D();
+                else
+                    DrawBG_Text(line, 0);
+            }
+        }
+        if ((DispCnt & 0x1000) && NumSprites)
+            InterleaveSprites(0x8000 | (i<<16));
+    }
+}
+
 void GPU2D::DrawScanline_BGOBJ(u32 line)
 {
     // forced blank disables BG/OBJ compositing
@@ -1376,7 +1398,6 @@ void GPU2D::DrawScanline_BGOBJ(u32 line)
     else
         memset(WindowMask, 0xFF, 256);
 
-    // TODO: what happens in mode 7? mode 6 on the sub engine?
     switch (DispCnt & 0x7)
     {
     case 0: DrawScanlineBGMode<0>(line); break;
@@ -1386,6 +1407,7 @@ void GPU2D::DrawScanline_BGOBJ(u32 line)
     case 4: DrawScanlineBGMode<4>(line); break;
     case 5: DrawScanlineBGMode<5>(line); break;
     case 6: DrawScanlineBGMode6(line); break;
+    case 7: DrawScanlineBGMode7(line); break;
     }
 
     // color special effects
diff --git a/src/GPU2D.h b/src/GPU2D.h
index b9a24224..6ad97830 100644
--- a/src/GPU2D.h
+++ b/src/GPU2D.h
@@ -135,6 +135,7 @@ private:
 
     template<u32 bgmode> void DrawScanlineBGMode(u32 line);
     void DrawScanlineBGMode6(u32 line);
+    void DrawScanlineBGMode7(u32 line);
     void DrawScanline_BGOBJ(u32 line);
 
     static void DrawPixel_Normal(u32* dst, u16 color, u32 flag);