Movement code for GameMaker using bbox_ variables and collision_line calls.

bbox_collision_line_move.gml

if (keyboard_check(vk_left)) repeat (3) {
    var _x = bbox_left - 1;
    if (!collision_line(_x, bbox_top, _x, bbox_bottom, obj_solid, false, true)) x -= 1;
}
if (keyboard_check(vk_right)) repeat (3) {
    var _x = bbox_right + 1;
    if (!collision_line(_x, bbox_top, _x, bbox_bottom, obj_solid, false, true)) x += 1;
}
if (keyboard_check(vk_up)) repeat (3) {
    var _y = bbox_top - 1;
    if (!collision_line(bbox_left, _y, bbox_right, _y, obj_solid, false, true)) y -= 1;
}
if (keyboard_check(vk_down)) repeat (3) {
    var _y = bbox_bottom + 1;
    if (!collision_line(bbox_left, _y, bbox_right, _y, obj_solid, false, true)) y += 1;
}