- fixed fillSimplePoly for indexed data.

On OpenGL this merely caused some visual glitches on the cheat automap - but the bad data in the buffer can make Vulkan abort entirely.

src/rendering/2d/v_2ddrawer.cpp

@@ -485,21 +485,22 @@ void F2DDrawer::AddPoly(FTexture *texture, FVector2 *points, int npoints,
 		mVertices[poly.mVertIndex+i].Set(points[i].X, points[i].Y, 0, u*uscale, v*vscale, color0);
 	}
 	poly.mIndexIndex = mIndices.Size();
-	poly.mIndexCount += (npoints - 2) * 3;
 
 	if (indices == nullptr || indexcount == 0)
 	{
+		poly.mIndexCount += (npoints - 2) * 3;
 		for (int i = 2; i < npoints; ++i)
 		{
 			AddIndices(poly.mVertIndex, 3, 0, i - 1, i);
 		}
 	}
 	else
 	{
+		poly.mIndexCount += (int)indexcount;
 		int addr = mIndices.Reserve(indexcount);
 		for (size_t i = 0; i < indexcount; i++)
 		{
-			mIndices[addr + i] = addr + indices[i];
+			mIndices[addr + i] = poly.mVertIndex + indices[i];
 		}
 	}