You’re playing with the Verifone eVo/Verix SDK, and are trying to draw a couple of lines on the screen. No big deal you think. You found the draw_line() function, read its (meager) documentation, and tried to use it. Unsuccessfully. Nothing is displayed. If draw_line() returns 0, you probably just messed up with the coordinates or you’re writing with the same color as the background. If the return value is -1, you need to check the errno value. Continue reading →