3D: Y-sorting

src/GPU3D.cpp

@@ -18,6 +18,7 @@
 
 #include <stdio.h>
 #include <string.h>
+#include <algorithm>
 #include "NDS.h"
 #include "GPU.h"
 #include "FIFO.h"
@@ -855,6 +856,10 @@ void SubmitPolygon()
     poly->VTop = vtop; poly->VBottom = vbot;
     poly->YTop = ytop; poly->YBottom = ybot;
     poly->XTop = xtop; poly->XBottom = xbot;
+
+    poly->SortKey = (ybot << 8) | ytop;
+    if (poly->Translucent) poly->SortKey |= 0x10000;
+
     poly->WShift = wshift;
     poly->WBuffer = (FlushAttributes & 0x2);
 
@@ -1791,9 +1796,21 @@ void VCount144()
 }
 
 
+bool YSort(Polygon* a, Polygon* b)
+{
+    // Y-sorting rules:
+    // * polygons with lower bottom Y come first
+    // * upon equal bottom Y, polygons with lower top Y come first
+    // * upon equal bottom AND top Y, original ordering is used
+
+    return a->SortKey < b->SortKey;
+}
+
 void VBlank()
 {
     if (FlushRequest)
+    {
+        if (NumPolygons)
         {
             // separate translucent polygons from opaque ones
 
@@ -1807,6 +1824,13 @@ void VBlank()
                     RenderPolygonRAM[io++] = poly;
             }
 
+            // apply Y-sorting
+
+            std::stable_sort(RenderPolygonRAM.begin(),
+                RenderPolygonRAM.begin() + ((FlushAttributes & 0x1) ? NumOpaquePolygons : NumPolygons),
+                YSort);
+        }
+
         RenderNumPolygons = NumPolygons;
 
         RenderDispCnt = DispCnt;

src/GPU3D.h

@@ -60,12 +60,12 @@ typedef struct
     bool IsShadowMask;
     bool IsShadow;
 
-    // data below rather specific to the software renderer
-
     u32 VTop, VBottom; // vertex indices
     s32 YTop, YBottom; // Y coords
     s32 XTop, XBottom; // associated X coords
 
+    u32 SortKey;
+
 } Polygon;
 
 extern u32 RenderDispCnt;

src/GPU3D_Soft.cpp

@@ -1677,10 +1677,6 @@ void ClearBuffers()
 
 void RenderPolygons(bool threaded, Polygon** polygons, int npolys)
 {
-    // sort polygons
-    // TODO: Y-sorting for translucent polygons
-    // TODO: all sorting should be done in GPU3D.cpp
-
     // polygons with ybottom>192 aren't rendered at all
 
     int j = 0;