Device Description

CRX-48Z (A2091A)

The CRX-48Z device has 48-image planes consisting of two buffers of 24 planes each, and 8-overlay planes. The screen resolution is 1280x1024 pixels. There is no offscreen memory in the frame buffer.

The hpcrx48z driver supports the following frame buffer configurations:

You can select each of the above configurations on a per-window basis. The configuration selected is a function of the depth of the window created and whether the window is in the overlay or image planes.

In the 8-bit indexed configurations, each pixel is used as an index into a 256-entry color map. Each entry in the color map provides eight bits per color (for red, green and blue components) providing a color palette of over 16 million colors. Double-buffering is achieved by switching between two banks of 8 planes.

In the 24-bit direct color configuration, each pixel is represented by eight bits per color channel. Double-buffering is achieved by dividing the 48 planes into two buffers of 24 planes. Double buffering of more than 8 planes is promoted to 24/24 double-buffering.

Dithering is used in depth 24 direct color visuals to improve color resolution.

Double-buffering with less than 8 planes (4/4, 3/3, 2/2,/1/1) is supported for compatibility with previous devices, however, it is not recommended. The write_enable and display_enable masks are used to accomplish double-buffering with less than 8 planes.

There are five different hardware color maps available on the CRX-48Z, which the X Server manages and allocates on a per-window basis. One of the color maps is shared by all overlay windows, and the remaining four are used by image windows.

Overlay Plane Rendering

Because of hardware restrictions, the hpcrx48z device driver cannot render to the overlay planes. If Starbase rendering to the overlay planes is required, the hpvmx driver must be used instead. For more information on Starbase rendering to the overlay planes, read the section "HP VMX: The CRX-family Overlay Plane Driver" in the chapter "HP VMX Device Driver."

Although the hpvmx driver is a fully functional PowerShade driver, only CMAP_NORMAL rendering is supported in the overlay planes of the CRX-48Z device. See below for comments about how the hpvmx driver is supported in CRX-48Z image planes. 8/8 double-buffering is also supported in the overlay planes using the hpvmx driver.

	NOTE: Color map index 255 is the overlay planes is the transparent index. Any pixels written with index 255 will display the image plane value at that location.

If an overlay plane window is gopened with a driver name of NULL, the hpvmx driver will be used. See Table 3-3, "Driver Selection at gopen" in the chapter "HP VMX Device Driver," for details.

Since the CRX-48Z device has only one color map for the overlay planes, the color map used by Starbase in an overlay window could potentially clash with the window system's color map. To avoid color map contention with the X Window System, overlay plane windows could be gopened WITHOUT doing an INIT or RESET_DEVICE (see gopen(3G) for details). Then, color map entries could be allocated from the X Server like an X client. See the section "Developing a Starbase Application" in the chapter "Using Starbase with the X Windows System" found in the Starbase Graphics Techniques manual for an example of how to do this.

In the image planes of the CRX-48Z device, the hpvmx driver is a fully functional PowerShade device driver, and supports CMAP_NORMAL, CMAP_MONOTONIC, and CMAP_FULL rendering, and well as double-buffering. However, the hpvmx driver is limited to depth 8 windows (it cannot render to depth 24 windows). The hpcrx48z driver does not support backing store. The hpvmx driver supports backing store only in the overlay planes.

While the hpvmx driver will work in the image planes of the CRX-48Z device, it is not recommended since the hpcrx48z device driver has significantly better performance in the image planes.

Optimized 3D Shaded Polygon Performance

The CRX-48Z provides optimized 3D shaded polygon performance. Shaded polygons on the CRX-48Z are highly optimized and very fast in most cases. See the file 〈starbase〉^[17]/PERF_NOTES for on-line PowerShade performance notes on features and performance data. This data is subject to change without notice.

In order to use VMX with PowerShade from a CRX-24Z or CRX-48Z graphics system, you must install the PowerShade software.