calculate hi-res vertex positions. reduces shaking of polygons when rendering at a higher res.

src/GPU3D.cpp

@@ -1194,6 +1194,16 @@ void SubmitPolygon()
         vtx->FinalPosition[0] = posX & 0x1FF;
         vtx->FinalPosition[1] = posY & 0xFF;
 
+        // hi-res positions
+        if (w != 0)
+        {
+            posX = ((((s64)(vtx->Position[0] + w) * Viewport[4]) << 4) / (((s64)w) << 1)) + (Viewport[0] << 4);
+            posY = ((((s64)(-vtx->Position[1] + w) * Viewport[5]) << 4) / (((s64)w) << 1)) + (Viewport[3] << 4);
+
+            vtx->HiresPosition[0] = posX & 0x1FFF;
+            vtx->HiresPosition[1] = posY & 0xFFF;
+        }
+
         vtx->FinalColor[0] = vtx->Color[0] >> 12;
         if (vtx->FinalColor[0]) vtx->FinalColor[0] = ((vtx->FinalColor[0] << 4) + 0xF);
         vtx->FinalColor[1] = vtx->Color[1] >> 12;

src/GPU3D.h

@@ -39,6 +39,10 @@ typedef struct
     s32 FinalPosition[2];
     s32 FinalColor[3];
 
+    // hi-res position (4-bit fractional part)
+    // TODO maybe: hi-res color? (that survives clipping)
+    s32 HiresPosition[2];
+
 } Vertex;
 
 typedef struct

src/GPU3D_OpenGL43.cpp

@@ -1120,9 +1120,13 @@ void BuildPolygons(RendererPolygon* polygons, int npolys)
             u32 zshift = 0;
             while (z > 0xFFFF) { z >>= 1; zshift++; }
 
+            u32 x = vtx->HiresPosition[0] >> 3;
+            u32 y = vtx->HiresPosition[1] >> 3;
+            *vptr++ = x | (y << 16);
+
             // TODO hires-upgraded positions?
             //*vptr++ = vtx->FinalPosition[0] | (vtx->FinalPosition[1] << 16);
-            *vptr++ = (vtx->FinalPosition[0] << 1) | (vtx->FinalPosition[1] << 17);
+            //*vptr++ = (vtx->FinalPosition[0] << 1) | (vtx->FinalPosition[1] << 17);
             //*vptr++ = (vtx->FinalPosition[0] << 2) | (vtx->FinalPosition[1] << 18);
             *vptr++ = z | (w << 16);