+/* This part of the viewer does :
+ * Draw horizontal lines, getting graphic context as arg.
+ * Copy region of the screen into another.
+ * Modify the boundaries to reflect a scale change. (resize)
+ * Refresh the physical screen with the pixmap
+ * A helper function is provided here to convert from time and process
+ * identifier to pixels and the contrary (will be useful for mouse selection).
+ * Insert an empty square in the drawing, moving the bottom part.
+ *
+ * The pixmap used has the width of the physical window, but the height
+ * of the shown processes.
+ */