MxVideoPresenter AlphaMask (formerly UnkStruct) (#226)

LEGO1/mxbitmap.cpp

@@ -369,7 +369,7 @@ MxResult MxBitmap::SetBitDepth(MxBool p_isHighColor)
 MxResult MxBitmap::StretchBits(HDC p_hdc, MxS32 p_xSrc, MxS32 p_ySrc, MxS32 p_xDest, MxS32 p_yDest, MxS32 p_destWidth, MxS32 p_destHeight)
 {
   // Compression fix?
-  if ((this->m_bmiHeader->biCompression != 16) && (0 < this->m_bmiHeader->biHeight)) {
+  if ((this->m_bmiHeader->biCompression != BI_RGB_TOPDOWN) && (0 < this->m_bmiHeader->biHeight)) {
     p_ySrc = (this->m_bmiHeader->biHeight - p_destHeight) - p_ySrc;
   }
 

LEGO1/mxbitmap.h

@@ -21,6 +21,13 @@ struct MxBITMAPINFO {
   RGBQUAD             bmiColors[256];
 };
 
+// Non-standard value for biCompression in the BITMAPINFOHEADER struct.
+// By default, uncompressed bitmaps (BI_RGB) are stored in bottom-up order.
+// You can specify that the bitmap has top-down order instead by providing
+// a negative number for biHeight. It could be that Mindscape decided on a
+// belt & suspenders approach here.
+#define BI_RGB_TOPDOWN      0x10
+
 // SIZE 0x20
 // VTABLE 0x100dc7b0
 class MxBitmap : public MxCore
@@ -43,6 +50,10 @@ public:
   virtual MxResult StretchBits(HDC p_hdc, MxS32 p_xSrc, MxS32 p_ySrc, MxS32 p_xDest, MxS32 p_yDest, MxS32 p_destWidth, MxS32 p_destHeight); // vtable+40
 
   inline BITMAPINFOHEADER *GetBmiHeader() const { return m_bmiHeader; }
+  inline MxLong GetBmiWidth() const { return m_bmiHeader->biWidth; }
+  inline MxLong GetBmiHeight() const { return m_bmiHeader->biHeight; }
+  inline MxLong GetBmiHeightAbs() const { return m_bmiHeader->biHeight > 0 ? m_bmiHeader->biHeight : -m_bmiHeader->biHeight; }
+  inline MxU8 *GetBitmapData() const { return m_data; }
 
 private:
   MxResult ImportColorsToPalette(RGBQUAD*, MxPalette*);

LEGO1/mxvideopresenter.cpp

@@ -2,7 +2,7 @@
 #include "MxVideoManager.h"
 
 DECOMP_SIZE_ASSERT(MxVideoPresenter, 0x64);
-DECOMP_SIZE_ASSERT(MxVideoPresenter::UnkStruct, 0xc);
+DECOMP_SIZE_ASSERT(MxVideoPresenter::AlphaMask, 0xc);
 
 // OFFSET: LEGO1 0x1000c700
 void MxVideoPresenter::VTable0x5c(undefined4 p_unknown1)
@@ -49,28 +49,116 @@ LPDIRECTDRAWSURFACE MxVideoPresenter::VTable0x78()
 // OFFSET: LEGO1 0x1000c7c0
 MxBool MxVideoPresenter::VTable0x7c()
 {
-  return (m_bitmap != NULL) || (m_unk54 != NULL);
+  return (m_bitmap != NULL) || (m_alpha != NULL);
 }
 
 // OFFSET: LEGO1 0x1000c7e0
 MxS32 MxVideoPresenter::GetWidth()
 {
-  return m_unk54 ? m_unk54->width
+  return m_alpha ? m_alpha->m_width
                  : m_bitmap->GetBmiHeader()->biWidth;
 }
 
 // OFFSET: LEGO1 0x1000c800
 MxS32 MxVideoPresenter::GetHeight()
 {
-  return m_unk54 ? m_unk54->height
+  return m_alpha ? m_alpha->m_height
                  : m_bitmap->GetBmiHeader()->biHeight;
 }
 
+// OFFSET: LEGO1 0x100b24f0
+MxVideoPresenter::AlphaMask::AlphaMask(MxBitmap &p_bitmap)
+{
+  m_width  = p_bitmap.GetBmiWidth();
+  // DECOMP: ECX becomes word-sized if these are not two separate actions.
+  MxLong _height = p_bitmap.GetBmiHeightAbs();
+  m_height = _height;
+
+  MxS32 size = ((m_width * m_height) / 8) + 1;
+  m_bitmask = new MxU8[size];
+  memset(m_bitmask, 0, size);
+
+  MxU32 biCompression = p_bitmap.GetBmiHeader()->biCompression;
+  MxU32 rows_before_top;
+  MxU8 *bitmap_src_ptr;
+
+  // The goal here is to enable us to walk through the bitmap's rows
+  // in order, regardless of the orientation. We want to end up at the
+  // start of the first row, which is either at position 0, or at
+  // (image_stride * biHeight) - 1.
+
+  // Reminder: Negative biHeight means this is a top-down DIB.
+  // Otherwise it is bottom-up.
+
+  if (biCompression == BI_RGB) {
+    // DECOMP: I think this must be an OR. If not, the check for
+    // biCompression == 16 gets optimized away.
+    if (biCompression == BI_RGB_TOPDOWN || p_bitmap.GetBmiHeight() < 0) {
+      rows_before_top = 0;
+    } else {
+      rows_before_top = p_bitmap.GetBmiHeightAbs();
+      rows_before_top--;
+    }
+
+    goto seek_to_last_row;
+  } else if (biCompression == BI_RGB_TOPDOWN) {
+    // DECOMP: This is the only condition where we skip the
+    // calculation below.
+    bitmap_src_ptr = p_bitmap.GetBitmapData();
+  } else {
+    if (p_bitmap.GetBmiHeight() < 0) {
+      rows_before_top = 0;
+    } else {
+      rows_before_top = p_bitmap.GetBmiHeightAbs();
+      rows_before_top--;
+    }
+
+// TODO: would prefer not to use goto if we can figure this structure out
+seek_to_last_row:
+    bitmap_src_ptr = ((p_bitmap.GetBmiWidth()+3)&-4) * rows_before_top + p_bitmap.GetBitmapData();
+  }
+
+  // How many bytes are there for each row of the bitmap?
+  // (i.e. the image stride)
+  // If this is a bottom-up DIB, we will walk it in reverse.
+  // TODO: Same rounding trick as in MxBitmap
+  MxS32 row_seek = ((m_height+3)&-4);
+  if (p_bitmap.GetBmiHeight() < 0)
+    row_seek = -row_seek;
+
+  // The actual offset into the m_bitmask array. The two for-loops
+  // are just for counting the pixels.
+  MxS32 offset = 0;
+
+  MxU8 *t_ptr = bitmap_src_ptr;
+  for (MxS32 j = 0; j < m_height; j++) {
+    for (MxS32 i = 0; i < m_width; i++) {
+      if (*t_ptr) {
+        // TODO: Second CDQ instruction for abs() should not be there.
+        MxU32 shift = abs(offset) & 7;
+        m_bitmask[offset / 8] |= (1 << abs(shift));
+      }
+      t_ptr++;
+      offset++;
+    }
+    // Seek to the start of the next row
+    bitmap_src_ptr += row_seek;
+    t_ptr = bitmap_src_ptr;
+  }
+}
+
+// OFFSET: LEGO1 0x100b26d0
+MxVideoPresenter::AlphaMask::~AlphaMask()
+{
+  if (m_bitmask)
+    delete[] m_bitmask;
+}
+
 // OFFSET: LEGO1 0x100b2760
 void MxVideoPresenter::Init()
 {
   m_bitmap = NULL;
-  m_unk54 = NULL;
+  m_alpha = NULL;
   m_unk5c = 1;
   m_unk58 = NULL;
   m_unk60 = -1;
@@ -99,7 +187,7 @@ void MxVideoPresenter::Destroy(MxBool p_fromDestructor)
     m_flags = m_flags & 0xfb;
   }
 
-  if (MVideoManager() && (m_unk54 || m_bitmap)) {
+  if (MVideoManager() && (m_alpha || m_bitmap)) {
     MxS32 height = GetHeight();
     MxS32 width = GetWidth();
 
@@ -112,7 +200,7 @@ void MxVideoPresenter::Destroy(MxBool p_fromDestructor)
   }
 
   delete m_bitmap;
-  delete m_unk54;
+  delete m_alpha;
 
   Init();
 

LEGO1/mxvideopresenter.h

@@ -49,16 +49,18 @@ public:
 
   // TODO: Not sure what this is. Seems to have size of 12 bytes
   // based on 0x100b9e9a. Values are copied from the bitmap header.
-  struct UnkStruct {
+  // SIZE 0xc
-    undefined unk0[4];
+  struct AlphaMask {
-    MxU16 width;
+    MxU8 *m_bitmask;
-    MxU16 height;
+    MxU16 m_width;
+    MxU16 m_height;
 
-    virtual ~UnkStruct() {}
+    AlphaMask(MxBitmap &);
+    virtual ~AlphaMask();
   };
 
   MxBitmap *m_bitmap;
-  UnkStruct *m_unk54;
+  AlphaMask *m_alpha;
   LPDIRECTDRAWSURFACE m_unk58;
   undefined2 m_unk5c;
   unsigned char m_flags; // 0x5e