TIA emulation is now more accurate wrt irregular scanline counts.

git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@2524 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba

Changes.txt

@@ -14,8 +14,13 @@
 
 3.7 to 3.7.1: (xxxx xx, 2012)
 
+  * Improved TIA emulation with ROMs that have too few or too many
+    scanlines; the output is now blanked as on a real TV.  Special thanks
+    to Omegamatrix of AtariAge for test ROMs in this area.
+
   * Fixed several bugs in DPC+ bankswitching scheme, including ability to
-    load and save state files.
+    load and save state files.  As well, ROMs now work correctly after
+    console format autodetection.
 
 -Have fun!
 

src/common/FBSurfaceTIA.cxx

@@ -199,6 +199,12 @@ void FBSurfaceTIA::update()
   myFB.myDirtyFlag = true;
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+void FBSurfaceTIA::invalidate()
+{
+  SDL_FillRect(myTexture, NULL, 0);
+}
+
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 void FBSurfaceTIA::free()
 {

src/common/FBSurfaceTIA.hxx

@@ -50,6 +50,7 @@ class FBSurfaceTIA : public FBSurface
     uInt32 getHeight() const { return myImageH; }
     void translateCoords(Int32& x, Int32& y) const;
     void update();
+    void invalidate();
     void free();
     void reload();
 

src/common/FrameBufferGL.cxx

@@ -332,6 +332,8 @@ bool FrameBufferGL::setVidMode(VideoMode& mode)
 void FrameBufferGL::invalidate()
 {
   p_gl.Clear(GL_COLOR_BUFFER_BIT);
+  if(myTiaSurface)
+    myTiaSurface->invalidate();
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/emucore/FrameBuffer.hxx

@@ -812,6 +812,12 @@ class FBSurface
     */
     virtual void update() { }
 
+    /**
+      This method should be called to reset the surface to empty
+      pixels / colour black.
+    */
+    virtual void invalidate() { }
+
     /**
       This method should be called to free any resources being used by
       the surface.

src/emucore/TIA.cxx

@@ -46,7 +46,6 @@ TIA::TIA(Console& console, Sound& sound, Settings& settings)
   : myConsole(console),
     mySound(sound),
     mySettings(settings),
-    myFrameWidth(160),
     myFrameYStart(34),
     myFrameHeight(210),
     myMaximumNumberOfScanlines(262),
@@ -194,8 +193,7 @@ void TIA::frameReset()
   // Calculate color clock offsets for starting and stopping frame drawing
   // Note that although we always start drawing at scanline zero, the
   // framebuffer that is exposed outside the class actually starts at 'ystart'
-  myFramePointerOffset = myFrameWidth * myFrameYStart;
-  myStartDisplayOffset = 0;
+  myFramePointerOffset = 160 * myFrameYStart;
 
   // NTSC screens will process at least 262 scanlines,
   // while PAL will have at least 312
@@ -209,7 +207,7 @@ void TIA::frameReset()
 
   // Reasonable values to start and stop the current frame drawing
   myClockWhenFrameStarted = mySystem->cycles() * 3;
-  myClockStartDisplay = myClockWhenFrameStarted + myStartDisplayOffset;
+  myClockStartDisplay = myClockWhenFrameStarted;
   myClockStopDisplay = myClockWhenFrameStarted + myStopDisplayOffset;
   myClockAtLastUpdate = myClockWhenFrameStarted;
   myClocksToEndOfScanLine = 228;
@@ -558,7 +556,7 @@ inline void TIA::startFrame()
 
   // Setup clocks that'll be used for drawing this frame
   myClockWhenFrameStarted = -1 * clocks;
-  myClockStartDisplay = myClockWhenFrameStarted + myStartDisplayOffset;
+  myClockStartDisplay = myClockWhenFrameStarted;
   myClockStopDisplay = myClockWhenFrameStarted + myStopDisplayOffset;
   myClockAtLastUpdate = myClockStartDisplay;
   myClocksToEndOfScanLine = 228;
@@ -622,22 +620,32 @@ inline void TIA::endFrame()
       myStopDisplayOffset = offset;
   }
 
-  // This is a bit of a hack for those ROMs which generate too many
-  // scanlines each frame, usually caused by VBLANK taking too long
-  // When this happens, the frame pointers sometimes get 'confused',
-  // and the framebuffer class doesn't properly overwrite data from
-  // the previous frame, causing graphical garbage
-  //
-  // We basically erase the entire contents of both buffers, making
-  // sure that they're also different from one another
-  // This will force the framebuffer class to completely re-render
-  // the screen
-  if(previousCount > myMaximumNumberOfScanlines &&
-     myScanlineCountForLastFrame <= myMaximumNumberOfScanlines)
+  // The following handle cases where scanlines either go too high or too
+  // low compared to the previous frame, in which case certain portions
+  // of the framebuffer are cleared to zero (black pixels)
+  // Due to the FrameBuffer class (potentially) doing dirty-rectangle
+  // updates, each internal buffer must be set slightly differently,
+  // otherwise they won't know anything has changed
+  // Hence, the front buffer is set to pixel 0, and the back to pixel 1
+
+  // Did we generate too many scanlines?
+  // (usually caused by VBLANK taking too long)
+  // If so, blank entire viewable area
+  if(myScanlineCountForLastFrame > 342 && previousCount <= 342)
   {
     memset(myCurrentFrameBuffer, 0, 160 * 320);
     memset(myPreviousFrameBuffer, 1, 160 * 320);
   }
+  // Did the number of scanlines decrease?
+  // If so, blank scanlines that weren't rendered this frame
+  else if(myScanlineCountForLastFrame < previousCount &&
+          myScanlineCountForLastFrame < 320 && previousCount < 320)
+  {
+    uInt32 offset = myScanlineCountForLastFrame * 160,
+           stride = (previousCount - myScanlineCountForLastFrame) * 160;
+    memset(myCurrentFrameBuffer + offset, 0, stride);
+    memset(myPreviousFrameBuffer + offset, 1, stride);
+  }
 }
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

src/emucore/TIA.hxx

@@ -188,9 +188,9 @@ class TIA : public Device
     /**
       Answers the width and height of the frame buffer
     */
-    uInt32 width() const  { return myFrameWidth;  }
-    uInt32 height() const { return myFrameHeight; }
-    uInt32 ystart() const { return myFrameYStart; }
+    inline uInt32 width() const  { return 160;           }
+    inline uInt32 height() const { return myFrameHeight; }
+    inline uInt32 ystart() const { return myFrameYStart; }
 
     /**
       Changes the current Height/YStart properties.
@@ -403,18 +403,12 @@ class TIA : public Device
     // (this is used when loading state files with a 'partial' frame)
     uInt32 myFramePointerClocks;
 
-    // Indicates the width of the visible scanline
-    uInt32 myFrameWidth;
-
     // Indicated what scanline the frame should start being drawn at
     uInt32 myFrameYStart;
 
     // Indicates the height of the frame in scanlines
     uInt32 myFrameHeight;
 
-    // Indicates offset in color clocks when display should begin
-    uInt32 myStartDisplayOffset;
-
     // Indicates offset in color clocks when display should stop
     uInt32 myStopDisplayOffset;