How to apply color and shading to an object using maya-api in c++

Question

i'd like to know how to apply color and shading to an object in c++ (using maya-api map a 2D texture), Here is my code:

MString MNEUT_FILE("G:/repos_cpp/data/eye_base.obj");
MGlobal::executeCommand(MString("file -import -namespace \"EYETemp\" -mergeNamespacesOnClash true") + "\"" + MNEUT_FILE + "\"");
MGlobal::executeCommand(MString("select \"EYETemp:*\""));
MGlobal::executeCommand(MString("rename ") + "eyeNeutral");

stat = MGlobal::executeCommand(MString("shadingNode -asShader lambert -name eyeball"));
stat = MGlobal::executeCommand(MString("sets -renderable true -noSurfaceShader true -empty -name lambert3SG"));
//stat = MGlobal::executeCommand(MString("defaultNavigation -connectToExisting -source eyeball -destination lambert3SG"));
stat = MGlobal::executeCommand(MString("connectAttr -f eyeball.outColor lambert3SG.surfaceShader"));
stat = MGlobal::executeCommand(MString("shadingNode -asTexture file -name eyeball_TGA"));
stat = MGlobal::executeCommand(MString("connectAttr -f eyeball_TGA.outColor eyeball.color"));
stat = MGlobal::executeCommand(MString("setAttr -type \"string\" eyeball_TGA.fileTextureName \"G:/repos_cpp/data/eyeball.TGA\""));
MGlobal::executeCommand(MString("select -r eyeNeutralShape"));
stat = MGlobal::executeCommand(MString("hyperShade -assign lambert3SG"));
if (!stat)
{
    cout << "error::8\n";
}
stat = MGlobal::executeCommand(MString("sets -e -fe lambert3SG eyeNeutralShape"));
if (!stat)
{
    cout << "error::9\n";
}

when i run this code the "error::8" always exist! would you like to tell me how to solve it. Thanks very much!

Answer 1

You only check the status of the last MGlobal::executeCommand so you can't know that's where it actually fails. You also do not check the error text to get an explanation for the error.

Consider making a wrapper that you use to check all calls:

#include <stdexcept>

MCommandResult MayaCmd(MString cmd) {
    MCommandResult retval;
    std::cout << "Executing MayaCmd: " << cmd << '\n';
    auto stat = MGlobal::executeCommand(cmd, retval);
    if(!stat) throw std::runtime_error(stat.errorString().asChar()); // or asUTF8()
    return retval;
}

You should then be able to execute your commands with little care and get an exception with an explanation as soon as something exceptional happens.

Example:

try {
    MayaCmd(MString("file -import -namespace \"EYETemp\" -mergeNamespacesOnClash true") + "\"" + MNEUT_FILE + "\"");
    MayaCmd("select \"EYETemp:*\"");
    MayaCmd("rename eyeNeutral");

    MayaCmd("shadingNode -asShader lambert -name eyeball");
    MayaCmd("sets -renderable true -noSurfaceShader true -empty -name lambert3SG");
    //MayaCmd("defaultNavigation -connectToExisting -source eyeball -destination lambert3SG");
    MayaCmd("connectAttr -f eyeball.outColor lambert3SG.surfaceShader");
    MayaCmd("shadingNode -asTexture file -name eyeball_TGA");
    MayaCmd("connectAttr -f eyeball_TGA.outColor eyeball.color");
    MayaCmd("setAttr -type \"string\" eyeball_TGA.fileTextureName \"G:/repos_cpp/data/eyeball.TGA\"");
    MayaCmd("select -r eyeNeutralShape");
    MayaCmd("hyperShade -assign lambert3SG");
    MayaCmd("sets -e -fe lambert3SG eyeNeutralShape");
}
catch(const std::exception& ex) {
    std::cout << "Exception: " << ex.what() << '\n';
}

I also suspect that the name you should use with hyperShade -assign is a name returned by one of the previous commands, perhaps shadingNode. Example:

auto ShaderNode = MayaCmd("shadingNode ...").stringResult();
...
MayaCmd("hyperShade -assign " + ShaderNode);