I am closer to a solution. Now I can get full keystone functionality, and movie 1 looks fine, but movie 2 fades to white instead of image, although if I set jit.gl.mesh @texture tex2, movie two fades in and out like I'd expect. I'd like to understand why mapping the texture to jit.gl.gridshape in the original crossfade example works, but mapping it to jit.gl.mesh in my version doesn't--isn't it all just geometry?
OK, I've got it working by applying the combined texture to a gridshape, capturing the gridshape to a new texture via sketch and then applying that texture to the keystone mesh. I don't understand why I don't have to bang the gridshape though... nor do I understand why I couldn't apply the combined texture directly to the mesh as in the previous attempt.