Explained Screen Pan Up/Down

Makefile

@@ -1,4 +1,4 @@
-VERSION=4.6
+VERSION=4.6a
 TARGNAME=A7800DS
 
 #---------------------------------------------------------------------------------

README.md

@@ -91,8 +91,8 @@ Controls :
  * B             : Fire button 2
  * SELECT        : SELECT Button
  * START         : PAUSE Button
- * X             : Fire button 2
- * Y             : Fire Button 1
+ * X             : Pan Screen Down
+ * Y             : Pan Screen Up
  * L/R + DPAD    : Used to Shift Offsets and Scale Screen to desired ratio
  * L + R + X     : Hold for 1 second to swap LCD screens top/bottom
   
@@ -108,7 +108,7 @@ Controls :
  I want to do as the game runs... so you must do it... the high scores will also
  auto-save if you quit the emulator or select a new game.
   
- Configuration :
+Configuration :
 ----------
 Generally you would use this to select a bankswitching scheme if the proper type wasn't auto-detected. 
 The following schemes are supported:
@@ -127,15 +127,6 @@ The following schemes are supported:
 * ABSOLETE            Only for the F-18 Hornet game by Absolete Entertainment
 * FRACTALUS           Only for the Rescue on Fractalus prototype (not a complete game but neat to see). This is EXRAM/A8.
 
-The X/Y screen settings can be tweaked to position the 7800 emulated screen on the DS screen as best you can. Unfortunately 
-the 7800 screen resolution isn't a perfect match for the DS 256x192 so you'll have to stretch and offset a bit. Most
-games have defaults that look good enough. Some games will cut off a few pixel lines at the top and bottom - but they will
-still be perfectly playalbe. Such is life with only 192 vertical pixels to play with on the DS!
-
-Recent versions of the emulator have a magnifying glass icon that will zoom and center the display to 1:1 of the actual 7800 output.
-This will crop some pixels off the sides and top/bottom but is useful to temporarily zoom up to enter things like high scores
-where the text may be hard to read when shrunk down.
-
 Frame Skipping can be OFF (show all frames), Moderate (Show 3/4 frames) or Agressive (only show 1/2 frames).  The latter is
 only really needed for the DS-Lite/Phat where the faster DSi CPU isn't available.
 
@@ -143,6 +134,43 @@ Don't touch the DMA Cycle Adjustment unless you understand them... and most peop
 
 Press START to save off your configuration - if you made changes you should re-load the game to ensure all settings are applied.
 
+Of Mice, Men and Screen Resolutions :
+----------
+The DS/DSi has a native screen resolution of 256x192. This is not ideal for the Atari 7800 where many of the games are 320 
+pixels across and often more than 192 scanlines. The original Atari NTSC spec called for 192 vertical scanlines and a few
+of the early games (Asteroids, Ms. Pac-Man, etc.) did stick to that but most later games utilize more vertical scanlines. 
+A typical NTSC TV can handle 230+ scanlines fairly well and so many of the Atari 7800 games utilize some number of extra
+scanlines to pack as much awesome gameplay as possible onto the screen.
+
+This is a problem for our hero, the DS/DSi. Fortunately the DS has the ability to scale/stretch as needed. But when doing
+so, there will be missing scanlines. For example, if the game utilizes 200 scalines but the DS can only show 192, there are 
+8 scanlines that must go missing... if scaled down to 192 pixels to fit the screen, these extra scalines might be in the
+middle of the playfield which is not great. If you scale the screen up (using Configuration options or the L/R shoulder 
+buttons in conjunction with the D-PAD to shift/scale the sceren), then some of the pixels (left or right, up or down) will
+be cropped off the screen. This might not be a big deal - sometimes the very top and bottom of a game are just clouds or 
+ground that can be safely cropped without any loss in gameplay. For many games, the top 16 pixels are the score / lives
+remaining.
+
+Most games have scaling defaults that look good enough. Some games will cut off a few pixel lines at the top and bottom - but
+they will still be perfectly playalbe.  However there are some thigns you can (and should!) do to help.
+
+Recent versions of the emulator have a magnifying glass icon that will zoom and center the display to 1:1 of the actual 7800 output.
+This will crop some pixels off the sides and top/bottom but is useful to temporarily zoom up to enter things like high scores
+where the text may be hard to read when shrunk down.
+
+More importantly, you can utilize the X and Y buttons as a pan down/up. This is massively useful for games that have a score at
+the top of the display (Galaxian, Space Invaders, Popeye, bonQ, etc).  Here you can stretch up the screen in the Y direction so
+that it is nearly 1:1 and shift the score off the top of the screen. Then, during gameplay, you can tap the X button to temporarily
+pan the display down so the score comes into view briefly... and it will magically shift back up after a half second. You can do
+this while you are playing - usually when you lose a life you can tap the X button to quickly glace at your score. This gives 
+more useable scanlines for actual gameplay. Think of this like you're at the arcade and you have to glance up to see your 
+score when focused on the field of play. It takes a little getting used to but this mechanism really helps map the more complicated
+game graphics onto the small sceren. Of course youc an always scale the screen down to it's totally visible - but there will be
+some loss of scanline information. Experiment and determine what works best for you.
+
+And remember - once you get your screen settings the way you want, be sure to go into the GEAR icon and hit START to save out
+your current configuration (which includes your screen offset/scaling tweaks on a per-game basis).
+
 --------------------------------------------------------------------------------
 Credits:
 --------------------------------------------------------------------------------

arm9/source/a7800utils.c

@@ -173,12 +173,15 @@ void FadeToColor(unsigned char ucSens, unsigned short ucBG, unsigned char ucScr,
 #define tchepres(a) \
    keyboard_data[GameConf.DS_Pad[a]] = 1;
 
+int16_t temp_shift __attribute__((section(".dtcm"))) = 0;
+uint8_t shiftTime = 0;
+
 ITCM_CODE void vblankIntr() 
 {
-  if (bRefreshXY)
+  if (bRefreshXY || temp_shift)
   {
     cxBG = (myCartInfo.xOffset << 8); 
-    cyBG = (myCartInfo.yOffset << 8);
+    cyBG = (myCartInfo.yOffset + temp_shift) << 8;
     xdxBG = ((320 / myCartInfo.xScale) << 8) | (320 % myCartInfo.xScale) ;
     ydyBG = ((video_height / myCartInfo.yScale) << 8) | (video_height % myCartInfo.yScale);
 
@@ -193,6 +196,20 @@ ITCM_CODE void vblankIntr()
     REG_BG3PD = ydyBG; 
 
     bRefreshXY = false;
+    
+    if (temp_shift)
+    {
+        ++shiftTime;
+        if (shiftTime > 40) 
+        {
+            if (temp_shift < 0) temp_shift++; else temp_shift--;
+            if (temp_shift == 0)
+            {
+                shiftTime = 0;
+                bRefreshXY = 1; // Force the next vBlank interrupt to put screen right
+            }
+        }
+    }    
   }
 }
 
@@ -1084,8 +1101,8 @@ ITCM_CODE void dsMainLoop(void)
         {
             if ( (keys_pressed & KEY_A) ) { tchepres(4); snes_adaptor &= 0xFEFF;}  // BUTTON #1
             if ( (keys_pressed & KEY_B) ) { tchepres(5); snes_adaptor &= 0xFFFE;}  // BUTTON #2
-            if ( (keys_pressed & KEY_Y) ) { tchepres(4); snes_adaptor &= 0xFFFD;}  // BUTTON #1
-            if ( (keys_pressed & KEY_X) ) { tchepres(5); snes_adaptor &= 0xFDFF;}  // BUTTON #2
+            if ( (keys_pressed & KEY_Y) ) { temp_shift = 16;}  // Shift Screen Down
+            if ( (keys_pressed & KEY_X) ) { temp_shift = -16;} // Shift Screen Up
         }
             
         if ((keys_pressed & KEY_R) || (keys_pressed & KEY_L))