Transparent and Alpha-blended Windows

VTScada supports transparent windows and alpha-blended (also referred to as translucent) windows.

Transparent Windows

A transparent window is one that has a transparent or invisible frame and background. The intended use for this feature is to allow the display of non-rectangular windows by rendering the background as transparent, while allowing mouse messages, such as movement and clicks, to "drill-through" the transparent area to the window below. Objects (such as graphics) placed on the transparent window remain opaque and mouse messages do not drill-through these opaque objects.

The simplest way to create a transparent window is to specify a background color less than zero (e.g. -1). The underlying implementation, however, requires that a specific color be used as the "key" color. All pixels of that color in the otherwise rectangular screen area that the window occupies are rendered as transparent. Using a background color of <0 results in the key color being black (i.e. RGB(0, 0, 0)), and the window background being set to that color. It may well be that you wish to have black as a color in your window, however. Therefore, setting bit 18 in the Window statement also announces that this window is to be rendered as transparent, with whatever color is specified as the background color being the transparent color.

Alpha-blended or Translucent Windows

An alpha-blended or translucent window is one that has an alpha channel set up in the final renderer, resulting in a translucent effect to the window (i.e. it behaves like a normal window, except that you can see through the window to some degree). The degree of translucency ranges from 0 (invisible) to 255 (completely opaque, like a normal window). Setting bit 17 on your Window statement invokes "automatic" alpha blending, where the window is set to be 50% translucent when inactive, and opaque when active. This is useful for dialogs that are non-modal A modal dialog is always displayed on top of the calling window and prevents further interaction with that window. and always on-top, so that when another window is active, you can see through the underlying windows. If you need a finer degree of control, do not set bit 17, but rather use a new value for the Option parameter of WindowOptions (9) and set the WindowOptions "OptValue" parameter to the degree of alpha-blending that you wish (0 to 255).

Neither the transparent nor the alpha-blended/translucent effects work with child windows. These effects are not designed for animation purposes, and are not sufficiently efficient for this purpose. The amount of processing power required to redraw one of these windows depends on the rating of the graphics card in your machine - the newer and faster the better.