6. Non-transitory computer-readable storage media storing instructions executable by one or more processors to perform operations comprising: displaying an electronic document on a touch screen of a portable computing device; defining at least a first region, a second region, and a third region associated with the touch screen; associating with the first region a previous page command to display a previous page of the electronic document; associating with the second region a command to display or hide a control object; associating with the third region a next page command to display a next page of the electronic document; detecting a first touch input in the second region; displaying the control object overlaid in front of the electronic document based at least in part on the first touch input, the control object displayed with an opacity set to a last used opacity level; detecting a second touch input representing a swiping movement on the touch screen; and controlling, by a processor of the portable computing device, a perceived visible brightness of the electronic document by increasing or decreasing the opacity of the control object based at least in part on a current opacity level of the control object and in part on a characteristic of the second touch input.
6. Non-transitory computer-readable storage media storing instructions executable by one or more processors to perform operations comprising: displaying an electronic document on a touch screen of a portable computing device; defining at least a first region, a second region, and a third region associated with the touch screen; associating with the first region a previous page command to display a previous page of the electronic document; associating with the second region a command to display or hide a control object; associating with the third region a next page command to display a next page of the electronic document; detecting a first touch input in the second region; displaying the control object overlaid in front of the electronic document based at least in part on the first touch input, the control object displayed with an opacity set to a last used opacity level; detecting a second touch input representing a swiping movement on the touch screen; and controlling, by a processor of the portable computing device, a perceived visible brightness of the electronic document by increasing or decreasing the opacity of the control object based at least in part on a current opacity level of the control object and in part on a characteristic of the second touch input. 7. The non-transitory computer-readable storage media of claim 6 , wherein the controlling comprises: decreasing the perceived visible brightness of the electronic document by increasing the opacity of the control object.