astrocade: support mid-screen updates w/ palette changes

doc/notes.txt

@@ -156,7 +156,6 @@ TODO:
   - switching platform of a repo?
   - make sure to flatten subdirs
 - astrocade
-  - what if update earlier part of screen with different palette? it'd be nice to have instant updates when debugging tho...
 - ctrl+alt+l on ubuntu locks screen
 
 WEB WORKER FORMAT

src/platform/astrocade.ts

@@ -103,14 +103,20 @@ const _BallyAstrocadePlatform = function(mainElement, arcade) {
   var palette = new Uint32Array(8);
   var palinds = new Uint8Array(8);
   var refreshlines = 0;
+  var dirtylines = new Uint8Array(arcade ? 262 : 131);
   var vidactive = false;
   var rotdata = new Uint8Array(4);
   var rotcount = 0;
   var intst = 0;
   
   function ramwrite(a:number, v:number) {
+    // set RAM
     ram.mem[a] = v;
-    ramupdate(a, v);
+    // mark scanline as dirty
+    dirtylines[Math.floor((a & 0xfff)/swbytes)] = 1;
+    // this was old behavior where we updated instantly
+    // but it had problems if we had mid-screen palette changes
+    //ramupdate(a, v);
   }
 
   function ramupdate(a:number, v:number) {
@@ -386,9 +392,14 @@ const _BallyAstrocadePlatform = function(mainElement, arcade) {
       }
       // refresh this line in frame buffer?
       if (sl < sheight && refreshlines>0) {
+        dirtylines[sl] = 0;
         refreshline(sl);
         refreshlines--;
       }
+      else if (dirtylines[sl]) {
+        dirtylines[sl] = 0;
+        refreshline(sl);
+      }
     }
     if (!novideo) {
       video.updateFrame(0, 0, 0, 0, swidth, verbl);