Although the late Steve Jobs dismissed talk of a Mac with a touchscreen display, an Apple patent (number 20120030626) at the U..S. Patent & Trademark Office shows that the company has considered/is considering the idea. The patent is for a computer with a touchscreen.

Per the patent, a control object including a knob element is displayed in a GUI [graphical user interface]. A first user input can be detected that indicates selection of the knob element. In response to the first user input, the knob element can be visually augmented. The visual augmentation can include displaying text labels of range limit values and a slider element with the knob element.

The slider element can include a fill bar to indicate the current value of the knob element. A second input can be a linear motion on or near the slider control. In response to the second user input, both the fill bar of the slider element and a fill portion of the knob element can be visually augmented to indicate the change in the value. A cursor image of a pointing device providing the second input can be hidden at least during the receiving of the second input.

Here's Apple's background on the invention: "Modern computer operating systems often provide a desktop graphical user interface for displaying various graphical objects. Some examples of graphical objects include windows, taskbars, docks, menus and various icons for representing documents, folders and applications. A user can interact with the desktop using a mouse, trackball, track pad or other known pointing device. If the GUI is touch sensitive, then a stylus or one or more fingers can be used to interact with the desktop.

Some computer applications include knobs, sliders and other controls that can be manipulated by a user through a pointing device or by touch input. For example, graphical objects emulating knobs and sliders of an audio mixing board or other hardware device can be included in the GUI of an audio or video application. The user can use a mouse or finger to rotate the knob control or move the slider control as desired to control a parameter of the application.

Many GUIs use knob controls to dial inputs up or down. However, traditional GUI knob controls typically have several drawbacks. For example, the interaction model of the knob control can be unclear, such that the user may not know whether to move a mouse pointer vertically, horizontally or in a circle to change the value of the knob control. Additionally, the resolution of a knob control may be less than other types of GUI controls (e.g., a slider control)."

The inventors are Michael Stephen Hopkins and Robert David Aron.