From 93ab7064b203c463607258cb3bc94f5da9729959 Mon Sep 17 00:00:00 2001
From: StapleButter <thetotalworm@gmail.com>
Date: Wed, 5 Jul 2017 19:31:13 +0200
Subject: 2D: implement large BG, fix non-large bitmap BG. fixes #61

---
 src/GPU2D.cpp | 126 ++++++++++++++++++++++++++++++++++++++++++++++++----------
 src/GPU2D.h   |   1 +
 2 files changed, 106 insertions(+), 21 deletions(-)

(limited to 'src')

diff --git a/src/GPU2D.cpp b/src/GPU2D.cpp
index a9bd498..ee1fbc1 100644
--- a/src/GPU2D.cpp
+++ b/src/GPU2D.cpp
@@ -934,7 +934,7 @@ void GPU2D::DrawScanlineBGMode6(u32 line, u32* spritebuf, u32* dst)
         {
             if (DispCnt & 0x0400)
             {
-                printf("GPU2D: MODE6 LARGE BG TODO\n");
+                DrawBG_Large(line, dst);
             }
         }
         if ((BGCnt[0] & 0x3) == i)
@@ -1387,20 +1387,6 @@ void GPU2D::DrawBG_Extended(u32 line, u32* dst, u32 bgnum)
     u16* pal;
     u32 extpal;
 
-    u32 coordmask;
-    u32 yshift;
-    switch (bgcnt & 0xC000)
-    {
-    case 0x0000: coordmask = 0x07800; yshift = 7; break;
-    case 0x4000: coordmask = 0x0F800; yshift = 8; break;
-    case 0x8000: coordmask = 0x1F800; yshift = 9; break;
-    case 0xC000: coordmask = 0x3F800; yshift = 10; break;
-    }
-
-    u32 overflowmask;
-    if (bgcnt & 0x2000) overflowmask = 0;
-    else                overflowmask = ~(coordmask | 0x7FF);
-
     extpal = (DispCnt & 0x40000000);
 
     s16 rotA = BGRotA[bgnum-2];
@@ -1415,20 +1401,40 @@ void GPU2D::DrawBG_Extended(u32 line, u32* dst, u32 bgnum)
     {
         // bitmap modes
 
+        u32 xmask, ymask;
+        u32 yshift;
+        switch (bgcnt & 0xC000)
+        {
+        case 0x0000: xmask = 0x07FFF; ymask = 0x07FFF; yshift = 7; break;
+        case 0x4000: xmask = 0x0FFFF; ymask = 0x0FFFF; yshift = 8; break;
+        case 0x8000: xmask = 0x1FFFF; ymask = 0x0FFFF; yshift = 9; break;
+        case 0xC000: xmask = 0x1FFFF; ymask = 0x1FFFF; yshift = 9; break;
+        }
+
+        u32 ofxmask, ofymask;
+        if (bgcnt & 0x2000)
+        {
+            ofxmask = 0;
+            ofymask = 0;
+        }
+        else
+        {
+            ofxmask = ~xmask;
+            ofymask = ~ymask;
+        }
+
         if (Num) tilemapaddr = 0x06200000 + ((bgcnt & 0x1F00) << 6);
         else     tilemapaddr = 0x06000000 + ((bgcnt & 0x1F00) << 6);
 
-        coordmask |= 0x7FF;
-
         if (bgcnt & 0x0004)
         {
             // direct color bitmap
 
             for (int i = 0; i < 256; i++)
             {
-                if ((!((rotX|rotY) & overflowmask)) && (windowmask[i] & (1<<bgnum)))
+                if (!(rotX & ofxmask) && !(rotY & ofymask) && (windowmask[i] & (1<<bgnum)))
                 {
-                    u16 color = GPU::ReadVRAM_BG<u16>(tilemapaddr + (((((rotY & coordmask) >> 8) << yshift) + ((rotX & coordmask) >> 8)) << 1));
+                    u16 color = GPU::ReadVRAM_BG<u16>(tilemapaddr + (((((rotY & ymask) >> 8) << yshift) + ((rotX & xmask) >> 8)) << 1));
 
                     if (color & 0x8000)
                         DrawPixel(&dst[i], color, 0x01000000<<bgnum);
@@ -1447,9 +1453,9 @@ void GPU2D::DrawBG_Extended(u32 line, u32* dst, u32 bgnum)
 
             for (int i = 0; i < 256; i++)
             {
-                if ((!((rotX|rotY) & overflowmask)) && (windowmask[i] & (1<<bgnum)))
+                if (!(rotX & ofxmask) && !(rotY & ofymask) && (windowmask[i] & (1<<bgnum)))
                 {
-                    u8 color = GPU::ReadVRAM_BG<u8>(tilemapaddr + (((rotY & coordmask) >> 8) << yshift) + ((rotX & coordmask) >> 8));
+                    u8 color = GPU::ReadVRAM_BG<u8>(tilemapaddr + (((rotY & ymask) >> 8) << yshift) + ((rotX & xmask) >> 8));
 
                     if (color)
                         DrawPixel(&dst[i], pal[color], 0x01000000<<bgnum);
@@ -1464,6 +1470,20 @@ void GPU2D::DrawBG_Extended(u32 line, u32* dst, u32 bgnum)
     {
         // mixed affine/text mode
 
+        u32 coordmask;
+        u32 yshift;
+        switch (bgcnt & 0xC000)
+        {
+        case 0x0000: coordmask = 0x07800; yshift = 7; break;
+        case 0x4000: coordmask = 0x0F800; yshift = 8; break;
+        case 0x8000: coordmask = 0x1F800; yshift = 9; break;
+        case 0xC000: coordmask = 0x3F800; yshift = 10; break;
+        }
+
+        u32 overflowmask;
+        if (bgcnt & 0x2000) overflowmask = 0;
+        else                overflowmask = ~(coordmask | 0x7FF);
+
         if (Num)
         {
             tilesetaddr = 0x06200000 + ((bgcnt & 0x003C) << 12);
@@ -1516,6 +1536,70 @@ void GPU2D::DrawBG_Extended(u32 line, u32* dst, u32 bgnum)
     BGYRefInternal[bgnum-2] += rotD;
 }
 
+void GPU2D::DrawBG_Large(u32 line, u32* dst) // BG is always BG2
+{
+    u8* windowmask = (u8*)&dst[256*2];
+    u16 bgcnt = BGCnt[2];
+
+    u32 tilesetaddr, tilemapaddr;
+    u16* pal;
+
+    u32 xmask, ymask;
+    u32 yshift;
+    switch (bgcnt & 0xC000)
+    {
+    case 0x0000: xmask = 0x1FFFF; ymask = 0x3FFFF; yshift = 9; break;
+    case 0x4000: xmask = 0x3FFFF; ymask = 0x1FFFF; yshift = 10; break;
+    case 0x8000: // TODO (most likely the second size bit is just ignored)
+    case 0xC000: printf("bad BG size for large BG: %04X\n", bgcnt); return;
+    }
+
+    u32 ofxmask, ofymask;
+    if (bgcnt & 0x2000)
+    {
+        ofxmask = 0;
+        ofymask = 0;
+    }
+    else
+    {
+        ofxmask = ~xmask;
+        ofymask = ~ymask;
+    }
+
+    s16 rotA = BGRotA[0];
+    s16 rotB = BGRotB[0];
+    s16 rotC = BGRotC[0];
+    s16 rotD = BGRotD[0];
+
+    s32 rotX = BGXRefInternal[0];
+    s32 rotY = BGYRefInternal[0];
+
+    if (Num) tilemapaddr = 0x06200000;
+    else     tilemapaddr = 0x06000000;
+
+    // 256-color bitmap
+
+    if (Num) pal = (u16*)&GPU::Palette[0x400];
+    else     pal = (u16*)&GPU::Palette[0];
+
+    for (int i = 0; i < 256; i++)
+    {
+        if (!(rotX & ofxmask) && !(rotY & ofymask) && (windowmask[i] & (1<<2)))
+        {
+            u8 color = GPU::ReadVRAM_BG<u8>(tilemapaddr + (((rotY & ymask) >> 8) << yshift) + ((rotX & xmask) >> 8));
+
+            if (color)
+                DrawPixel(&dst[i], pal[color], 0x01000000<<2);
+        }
+
+        rotX += rotA;
+        rotY += rotC;
+    }
+
+    BGXRefInternal[0] += rotB;
+    BGYRefInternal[0] += rotD;
+}
+
 void GPU2D::InterleaveSprites(u32* buf, u32 prio, u32* dst)
 {
     u8* windowmask = (u8*)&dst[256*2];
diff --git a/src/GPU2D.h b/src/GPU2D.h
index 289f1fe..4c68cdb 100644
--- a/src/GPU2D.h
+++ b/src/GPU2D.h
@@ -114,6 +114,7 @@ private:
     void DrawBG_Text(u32 line, u32* dst, u32 bgnum);
     void DrawBG_Affine(u32 line, u32* dst, u32 bgnum);
     void DrawBG_Extended(u32 line, u32* dst, u32 bgnum);
+    void DrawBG_Large(u32 line, u32* dst);
 
     void InterleaveSprites(u32* buf, u32 prio, u32* dst);
     void DrawSprites(u32 line, u32* dst);
-- 
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