## write an asymptote program for recreating a triangular mesh
## scene. Color and transparency are supported; mesh drawing, color2,
## and material properties are not currently supported. The loops
## could be vectorized but seem adequate for now.

saveTrianglesAsASY <- function(scene, filename = "scene.asy") {
    scene <- misc3d:::colorScene(scene)
    triangles <- misc3d:::canonicalizeAndMergeScene(scene, "color",
                                                    "color2", "alpha",
                                                    "col.mesh", "fill",
                                                    "smooth")
    ve <- misc3d:::t2ve(triangles)
    f <- file(filename, open = "w")
    on.exit(close(f))

    ## write out header information and vertices
    cat("//generated by saveTrianglesAsASY\n\n",
        "import three;\n\n",
        "size(20cm);\n\n",
        "//currentprojection=perspective(250,-250,250);\n",
        "currentlight=Viewport;\n\n",
        "typedef path3[] trimesh;\n\n",
        "// Vertices\n",
        "triple[] V;\n",
        sep = "", file = f)

    nv <- ncol(ve$vb)
    x <- ve$vb[1,]
    y <- ve$vb[2,]
    z <- ve$vb[3,]
    for (i in 1 : nv)
        cat(sprintf("V[%d] = (%f, %f, %f);\n",
                    i - 1, x[i], y[i], z[i]), file = f)

    ## write out the faces
    cat("\n",
        "guide3 triface_(int i, int j, int k) {\n",
        "  guide3 gh; gh=V[i-1]--V[j-1]--V[k-1]--cycle;\n",
        "  return gh;\n",
        "};\n\n",
        "// Faces\n",
        "trimesh F;\n",
        sep = "", file = f)

    nf <- ncol(ve$ib)
    v1 <- ve$ib[1,]
    v2 <- ve$ib[2,]
    v3 <- ve$ib[3,]
    for (i in 1 : nf)
        cat(sprintf("F[%d] = triface_(%d, %d, %d);\n",
                    i - 1, v1[i], v2[i], v3[i]), file = f)

    ## write out color and transparency values
    cat("\n",
        "// Colors\n",
        "material M[];\n",
        sep = "", file = f)

    cols <- col2rgb(triangles$color)
    alpha <- triangles$alpha
    r <- cols[1,]
    g <- cols[2,]
    b <- cols[3,]
    if (any(alpha < 1))
        for (i in 1 : nf)
            cat(sprintf("M[%d] = rgb(%f, %f, %f) + opacity(%f);\n",
                        i - 1, r[i], g[i], b[i], alpha[i]),
                file = f)
    else
        for (i in 1 : nf)
            cat(sprintf("M[%d] = rgb(%f, %f, %f);\n",
                        i - 1, r[i], g[i], b[i]),
                file = f)

    cat("\ndraw(surface(F), M);\n", file = f)
    invisible(NULL)
}