GDDM display limitations

GDDMXD/MVS appears as an IBM® 3179G device model to the GDDM® application. When the HostRast option is active, the device model is IBM 3279. The IBM 3179 Model G Color Graphics Display Station is used regardless of the display device nickname presented by the application.

The following are characteristics of the GDDMXD/MVS IBM 3179G display station:

Alphanumeric Cursor

When the graphics cursor is not enabled, the alphanumeric cursor can be repositioned by pointing the X Window System pointer device cursor for the GDDMXD window at the wanted character location and pressing the pointing device button.

Attached Graphics Cursor

When the graphics cursor is attached, the X Window System pointer device cursor for the GDDMXD window changes to a crosshair pattern and moves as the pointer device is moved.

Blinking Character Attribute

Ignores the blinking character attribute.

Character Display

Characters with an EBCDIC value of less than hex 40 are displayed as blanks.

Color Mixing

GDDMXD/MVS supports only the overpaint foreground color mix mode. The initial color of the image area is black, and mixing with the actual background colors is not performed.

An exception is made for data passed by an image data order. In this exception, a combined foreground color mix mode is supported, if the series of begin image orders have exactly the same parameter values.

When the HostRast option is active, color mixing is performed by GDDM, and the preceding exception does not apply.

Default Vector Symbol Set

The Default Vector Symbol Set is not supported.

Detached Graphics Cursor

When the graphics cursor is detached by the data stream or is not attached, the X Window System pointer device cursor for the GDDMXD window changes to an open arrow when the keyboard is unlocked, or changes to an X shape when the keyboard is locked.

Detectable Fields

Ignores the detectable fields.

Pixel Spacing

When the HostRast option is not active, the vertical and horizontal pixel spacing of the actual display device that is obtained from the X Window System is supplied to the GDDM application. When the HostRast option is active, the pixel spacing of an IBM 3279 Color Display Station is supplied to the GDDM application.

Visual Appearance

For all programmed symbol and image data that is received from the GDDM application, each GDDM pixel is mapped to one X Window System display pixel, which causes a different appearance from the same data stream displayed on an IBM 3179G Color Graphics Display Station. This map process can also cause display differences in the placement of alphanumeric field data over the graphics display and in the appearance of the filled areas of the graphic display. When the HostRast option is active, aspect ratio distortion of the displayed graphics appears, unless the aspect ratio of the X Window System display is the same as the IBM 3279.