This section summarizes PC 98 guidelines related to 2-D DirectDraw graphics features, which can be implemented as hardware acceleration features.
Entertainment PC 98 systems require hardware acceleration for 2-D graphics. Individual items in this section are marked as required or recommended for that system type.
In general, hardware acceleration for 2-D graphics is not required for Office PC 98 systems. The specific items in this section are required or recommended only if a hardware manufacturer chooses to implement hardware acceleration in a graphics adapter. For workstations, it is recommended that the OEM choose graphics adapters that provide hardware acceleration to support high-quality graphics for use with professional graphics applications.
The items for DirectDraw acceleration in this section are presented in order of importance.
19. Frame buffer can be accessed directly by applications
Consumer PC 98
Office PC 98
Entertainment PC 98
Required
Required
Required
The visible frame buffers must be accessible. It must be possible for applications to perform direct frame buffer accesses at any time, even while asynchronous accelerator operations are being executed. Without this capability, drivers cannot support DirectDraw or Direct3D on Windows NT, and operations on Windows will not be fully robust.
Some hardware keeps the information in its frame buffers in a format that does not correspond to the linear format that is standard in DirectDraw, such as tiling the pixels to exploit the 2-D coherence of image data. If this is the case, the hardware must perform translations so that DirectDraw surfaces that are being accessed directly appear linear. The hardware performing this translation might be a limited resource, but it must be able to perform translations on at least seven DirectDraw surfaces simultaneously. Support for eight surfaces is recommended.
20. Adapter and driver support linear-mapped, low-resolution modes
Consumer PC 98
Office PC 98
Entertainment PC 98
Required
Required
Required
This is required for all PC 98 system types, including systems with LCD displays. All graphics adapters currently support linear-mapped low-resolution modes. There is minimal additional driver work to support this.
Decreasing the size of the frame buffer decreases the average polygon size and increases the frame rate for a given scene. These additional modes provide support for software rendering games and software Direct3D.
If low-resolution support is implemented in the hardware, the following low-resolution modes are required:
| 320 × 200 × 16 bpp 320 × 200 × 8 bpp |
320 × 240 × 16 bpp 320 × 240 × 8 bpp |
640 × 400 × 16 bpp 640 × 400 × 8 bpp |
The following low-resolution modes are recommended:
| 400 × 300 × 16 bpp 400 × 300 × 8 bpp |
512 × 384 × 16 bpp 512 × 384 × 8 bpp |
Note: In Windows, low-resolution capabilities must not be defined in the registry so that they do not appear in the display control panel. In Windows NT, the control panel automatically filters out these modes.
21. Adapter supports transparent blter
Consumer PC 98
Office PC 98
Entertainment PC 98
Required
Required
Required
This is required for all PC 98 system types. There is no restriction on source size. A transparent blter can perform a blt with a source key transparent color. This assumes that the blter is asynchronous with the host processor.
22. Hardware supports double buffering with no tearing
Consumer PC 98
Office PC 98
Entertainment PC 98
Required
Required
Required
This is required for all PC 98 system types and must be performed in synchronization with the VBI.
The hardware must support a mechanism for swapping buffers without visible artifacts such as “tearing.” The mechanism for doing this is at the discretion of the hardware designer, but it should support tear-free double buffering for both full-screen and non-occluded windowed applications.
Notice that the blts must be performed in synchronization with the vertical scan line to avoid tearing. The ability to read the current scan line supports blting or writing to the screen without tearing. Also, in some contexts such as video playback, this support eliminates the need for a back buffer.
For information about the upper limits of resolution to be supported, see the requirement, “Screen resolution and local memory capacity meet PC 98 requirements,” earlier in this chapter.
23. Hardware supports programmable blter stride
Consumer PC 98
Office PC 98
Entertainment PC 98
Required
Recommended
Required
This is required for all PC 98 system types as part of the required support for textures. A programmable blter stride ensures that Windows can use linear memory. A fixed stride forces Windows to use rectangular memory management, with all the related inefficiencies. It must be possible to specify different strides for the source and destination on blts.