Drawing a line at a given angle
Use trigonometry (sin() and cos()) functions to get the right x and y coordinates.
I would consider replacing your drawLine() command with something like this (untested) assuming the tiltAngle is in degrees from -90 to +90 (with 0 degrees is straight up) and you want to draw a line at this angle from the origin (63, 63) with a radius of 64.
float tiltAngleRad = tiltAngle * DEG_TO_RAD; // convert angle to radians
int xEnd = 63 + 64 * sin (tiltAngleRad); // Ending x-coordinate offset &amp; radius
int yEnd = 63 - 64 * cos (tiltAngleRad); // Ending y-coordinate offset &amp; radius
display.drawLine (63, 63, xEnd, yEnd);

You might have to experiment with the offset and radius but I believe this will get you close yo what you want.