I'm trying to use ConTeXt with Metafun to produce a map of a videogame I
am working on. In fact I did it 9 years ago but it seems that now it
doesn't work.

I have two 32 pixels wide by 40 pixels high sprites. They are saved in the
skysprite.png and sandsprite.png files. Since 32 = 4 x 8 and 40 = 5 x 8,
the width/height ratio is 4/5.

This should produce a page with a sky sprite and a sand sprite, one
below the other. It worked in the past. Each sprite should be 4 x 0.095 cm
= 0,38 cm wide and 5 x 0.095 cm = 0.475 cm high:

\starttext
\setupMPinstance[metafun][textstyle={\switchtobodyfont[termes,8pt]}]
\startuseMPgraphic{mapa}
u:=.095cm;
draw externalfigure "./skysprite.png" xscaled 4u yscaled 5u shifted
(0u,-0u);
draw externalfigure "./sandsprite.png" xscaled 4u yscaled 5u shifted
(0u,-5u);
\stopuseMPgraphic
\useMPgraphic{mapa}
\stoptext

But instead I got two huge sprites of 2.8 cm x 4.4 cm.

Am I forgetting something?

Thanks