How about using the iCustom function.

sngSlope0 = NormalizeDouble(iCustom(NULL, 0, "Slope Direction Line", 80, 3, 0, 0, 0), 4);
sngSlope1 = NormalizeDouble(iCustom(NULL, 0, "Slope Direction Line", 80, 3, 0, 1, 0), 4);

if (sngSlope1>=sngSlope0) {
// Long
}
else {
// Short
}

If you have the .mq4 code for the indicator, you can use the iCustom function. I'm assuming "Slope Direction Line.mq4" is the name of the indicator you are using.