Function tiles is similar to tile but tile sizes is determined by another data. This allows one to simulate transparency of the plot.
MGL code:
call 'prepare2d' subplot 1 1 0 '':title 'Tiles plot':box:tiles a b
C++ code:
void smgl_tiles(mglGraph *gr) { mglData a,b; mgls_prepare2d(&a,&b); if(big!=3) {gr->SubPlot(1,1,0,""); gr->Title("TileS plot");} gr->Box(); gr->TileS(a,b); }