Figure 2.4.1.4.2a: The Overlay opacity controls.
Multiple overlays can be stacked on top of each other, and all overlays are stacked on top of the background of the Snapshot. To enable the user to control which Overlays are seen and how much of the background is seen, EClass provides opacity controls for each Overlay. There are two opacity controls for each Overlay - one to control the background of the overlay (how much of what's behind it is seen), and one to control the transparency of the shapes drawn on the Overlay. Figure 2.4.1.4.2a shows a closeup of the Overlay opacity controls and details which control preforms which operation.
Figure 2.4.1.4.2a: The Overlay opacity controls.
The above figure shows the background opacity control set to the minimum, and the shape opacity control set to full. This means that this Overlay has a fully transparent background and the drawings contained in it are fully opaque. Figure 2.4.1.4.2b shows a Snapshot with two Overlays, both of which have the same opacity settings as the above example.
Figure 2.4.1.4.2b: A Snapshot with two Overlays.
In the above example, since both Overlay's background opacities are set to 0, the background Snapshot is visible behind the Overlay shapes. Likewise, both of the Overlay's have full opacity set for their shapes, so the shapes are fully opaque.
To change an opacity setting for an Overlay, the user clicks and drags on the desired opacity slider until it has reached the appropriate setting. The following figures show the means and effect of changing the background opacity of the Overlay containing the rectangle to 100%.
Figure 2.4.1.4.2c: The user clicks on the background opacity slider.
Figure 2.4.1.4.2d: The user drags the slider to 50%.
Figure 2.4.1.4.2e: The user drags and releases the slider at 100%.
As the user drags the opacity slider to the right, the snapshot of the lecture becomes less visible. Since this Overlay is the bottom-most Overlay in the Snapshot, none of the other Overlays are affected. Background opacity settings can only affect Overlays ordered under them within the Snapshot (See Section 2.4.1.4.1 for details on Overlay ordering). To make the Overlay containing the rectangle the only visible Overlay, the user drags the background opacity control for that Overlay to 100%. In response, all Overlays under this Overlay are hidden; Figure 2.4.1.4.2f shows the result of this action.
Figure 2.4.1.4.2f: All other Overlays are now hidden.
To affect the opacity level for the drawings on an Overlay, the user clicks and drags the shape opacity slider. The following figures show the means and effect of changing the shape opacity of the Overlay containing the rectangle to 0%. The following figures assume that both Overlays have background opacities of 0%.
Figure 2.4.1.4.2g: The user clicks on the shape opacity slider.
Figure 2.4.1.4.2h: The user drags the slider to 50%.
Figure 2.4.1.4.2i: The user drags and releases the slider at 0%.
As the user drags the shape opacity slider to the left, the shapes on the Overlay become less visible. This can be useful for hiding the content of Overlays from other users on a shared Snapshot.