Find the Bug A Book of Incorrect Programs

Draw a Triangle on the Screen, Part I

This function draws a triangle on the screen. It becomes the core of an applet that allows the user to pick the three endpoints by clicking three times on the screen, which will be completed in the next example.

The algorithm assumes that the three points are ordered by x coordinate. It fills the triangle by drawing a series of vertical lines, 1 pixel wide. To do this, it splits the triangle into a “left” and “right” half; that is, the part from the x coordinate of the first point to the x coordinate of the second point, and the part from the x coordinate of the second point to the x coordinate of the third ...