The POWER Gt4 and POWER Gt4x adapters are available in 16-bit (double-buffered 8-bit), and 48-bit (double-buffered 24-bit) configurations. Both adapters occupy 2 or 3 Micro Channel slots and support a 24-bit z-buffer.
Both adapters accelerate graphics line and polygon drawing speeds by using a custom very large scale integration (VLSI) raster subsystem, multiple digital signal processor (two on the POWER Gt4 and six on the POWER Gt4x), and a custom, high-speed VLSI interface chip. In addition to drawing speeds, these adapters optimize context switching (the servicing of drawing orders in multiple windows simultaneously) performance by supporting 16 independent logical first-in-first-out queues (FIFOs) and 16 graphics contexts resident on the adapter.
The POWER Gt4 and POWER Gt4x are functionally identical. The only difference between these two adapters is the number of onboard digital signal processors, which affects the overall drawing speeds. The POWER Gt4 and POWER Gt4x are available in two configurations:
The 48-bit POWER Gt4 and POWER Gt4x adapters each contain two 24-bit main frame buffers, 2 overlay bitplanes, and a 24-bit z-buffer. In double-buffered RGB mode, one 24-bit buffer is displayed, while the other is used for rendering. The POWER Gt4 and POWER Gt4x support multiple per-window hardware gamma ramps. In particular, while in RGB mode, the gamma ramp for one window can be changed independently of the others, thus leading to new visualization capabiltities. In color map mode, these adapters each support an 8-bit (256-entry) output color lookup table.
The 16-bit POWER Gt4 and POWER Gt4x adapters each contain two 8-bit main frame buffers, 2 overlay bitplanes, and a 24-bit z-buffer. When in double-buffer mode, one 8-bit buffer is displayed, while the other is used for rendering. In single-buffer mode, the single buffer is 8 bits deep. Double-buffered color-index and double-buffered RGB modes are both supported, the latter by 332 dithering. Like the 48-bit POWER Gt4 and POWER Gt4x, the 16-bit adapters support per-window gamma ramps. In color-map mode, these adapters each support an 8-bit (256-entry) output color lookup table.
The 24-bit POWER GXT1000 adapter is available in double-buffered 12-bit color-index or double-buffered 8-bit RGB mode; the 48-bit POWER GXT1000 adapter is available in double-buffered 12-bit color-index or double-buffered 24-bit RGB mode. Both adapters support 24-bit z-buffer and 8-bit overlay planes. Graphics rendering speeds are accelerated by both adapters by using a custom VLSI raster subsystem and multiple digital signal processors.
Note: Valid z-buffer ranges on the POWER Gt4 and POWER Gt4x adapters are 0x0 to 0xffffff, and not the usual GL ranges -0x800000 to +0x7fffff.
Affected subroutines include the following: