How to combine 3D Graphics?

[Jee Lou]

I have tried to combine a translucent 3D-plot graph with its density plot by using Show. But it doesn't work. Here's my code:
g1=Plot3D[Sin[x + y], {x, 0, Pi}, {y, 0, Pi}, Mesh -> False,PlotStyle->Opacity[.5]];
g2=DensityPlot[Sin[x + y], {x, 0, Pi}, {y, 0, Pi}, Frame -> False];
g3=Plot3D[-1, {x, 0, Pi}, {y, 0, Pi}, Mesh -> None,TextureCoordinateFunction -> ({#1, #2} &), PlotStyle -> Directive[Texture[g2]]];
Show[g1,g3]
It turns out that the density graph disappears T_T.
How can I make it right? 

[Chunguang Li]

Jee Lou,

    In fact, you can let Opacity[.5] be Opacity[.05], make g1 is more transparent, then you can get the density graph clearly.

Li Chunguang.

在 2012年5月10日星期四 UTC+8下午4:49:05，Jee Lou写道：