gba: improve handling of OBJ mosaic counters

Author: png183

ares/gba/ppu/object.cpp

@@ -6,7 +6,14 @@ auto PPU::Objects::setEnable(n1 status) -> void {
 auto PPU::Objects::scanline(u32 y) -> void {
   if(y >= 160) return;
 
-  mosaicOffset = 0;
+  hmosaicOffset = io.mosaicWidth;
+  if(y == 0 || vmosaicOffset == io.mosaicHeight) {
+    vmosaicOffset = 0;
+    mosaicY = y;
+  } else {
+    vmosaicOffset++;
+  }
+
   auto& buffer = lineBuffers[y & 1];
   for(auto& pixel : buffer) pixel = {};
   if(ppu.io.forceBlank[1] || cpu.stopped() || !io.enable[1]) return;  //checks if display conditions will be met next scanline
@@ -16,8 +23,7 @@ auto PPU::Objects::scanline(u32 y) -> void {
     if(object.affine == 0 && object.affineSize == 1) continue;  //hidden
     if(py >= object.height << object.affineSize) continue;  //offscreen
 
-    if(object.mosaic && io.mosaicHeight) {
-      s32 mosaicY = (y / (1 + io.mosaicHeight)) * (1 + io.mosaicHeight);
+    if(object.mosaic) {
       py = object.y >= 160 || mosaicY - object.y >= 0 ? u32(mosaicY - object.y) : 0;
     }
 
@@ -97,15 +103,17 @@ auto PPU::Objects::outputPixel(u32 x, u32 y) -> void {
 
   auto& buffer = lineBuffers[y & 1];
   output = buffer[x];
-  
-  //horizontal mosaic
-  if(!mosaicOffset) {
-    mosaicOffset = 1 + io.mosaicWidth;
+
+  if(hmosaicOffset == io.mosaicWidth) {
+    hmosaicOffset = 0;
     mosaic = output;
-  } else if(!mosaic.mosaic || !output.mosaic || (output.priority < mosaic.priority)) {
+  } else {
+    hmosaicOffset++;
+  }
+
+  if(!mosaic.mosaic || !output.mosaic || (output.priority < mosaic.priority)) {
     mosaic = output;
   }
-  mosaicOffset--;
 }
 
 auto PPU::Objects::power() -> void {
@@ -115,5 +123,7 @@ auto PPU::Objects::power() -> void {
   }
   output = {};
   mosaic = {};
-  mosaicOffset = 0;
+  mosaicY = 0;
+  hmosaicOffset = 0;
+  vmosaicOffset = 0;
 }

ares/gba/ppu/ppu.hpp

@@ -202,14 +202,16 @@ struct PPU : Thread, IO {
 
       n1 hblank;   //1 = allow access to OAM during Hblank
       n1 mapping;  //0 = two-dimensional, 1 = one-dimensional
-      n5 mosaicWidth;
-      n5 mosaicHeight;
+      n4 mosaicWidth;
+      n4 mosaicHeight;
     } io;
 
     Pixel lineBuffers[2][240];
     Pixel output;
     Pixel mosaic;
-    u32 mosaicOffset;
+    s32 mosaicY;
+    n4 hmosaicOffset;
+    n4 vmosaicOffset;
   } objects;
 
   struct Window {

ares/gba/ppu/serialization.cpp

@@ -66,7 +66,9 @@ auto PPU::Objects::serialize(serializer& s) -> void {
   s(io.mosaicWidth);
   s(io.mosaicHeight);
 
-  s(mosaicOffset);
+  s(mosaicY);
+  s(hmosaicOffset);
+  s(vmosaicOffset);
 }
 
 auto PPU::Window::serialize(serializer& s) -> void {

ares/gba/system/serialization.cpp

@@ -1,4 +1,4 @@
-static const string SerializerVersion = "v147";
+static const string SerializerVersion = "v148";
 
 auto System::serialize(bool synchronize) -> serializer {
   if(synchronize) scheduler.enter(Scheduler::Mode::Synchronize);