driver.video.doublebuffer¶

Double-buffered rendering using SSE-accelerated memory copy.

Overview¶

This unit implements double-buffered rendering for the video subsystem. It allocates a back buffer in kernel memory, redirects drawing operations to the back buffer, and provides a Flush procedure that copies the completed back buffer to the front (visible) framebuffer using SSE 128-bit memory copy instructions for maximum throughput.

Dependencies¶

driver.video
driver.video.types
core.memory
core.sse
syslog

Constants¶

COPY_WIDTH¶

Value: 128. The SSE copy granularity in bits (16 bytes per operation), used by the __SSE_128_memcpy routine.

Functions and Procedures¶

allocateBackBuffer¶

function allocateBackBuffer(size: uint32): pointer;

Allocates a physically contiguous back buffer of size bytes using klalloc (large kernel allocation). Returns the base address, or nil on failure.

initBackBuffer¶

procedure initBackBuffer(VideoInterface: PVideoInterface);

Allocates a back buffer matching the front buffer's dimensions and BPP, fills in VideoInterface^.BackBuffer, and sets VideoInterface^.DefaultBuffer to point at the back buffer.

Flush¶

procedure Flush(Front, Back: PVideoBuffer);

Copies the entire back buffer to the front buffer using __SSE_128_memcpy in 128-bit (16-byte) chunks. The buffer size must be a multiple of 16 bytes; the framebuffer dimensions are chosen to satisfy this requirement.

enable¶

procedure enable(VideoInterface: PVideoInterface);

Calls initBackBuffer, then replaces VideoInterface^.DrawRoutines.Flush with @Flush. Registered as the 'BASIC_DOUBLE_BUFFER' driver in driver.video.

Notes¶

klalloc is used rather than the standard kernel allocator because the back buffer may be several megabytes; this requires a large contiguous allocation that the slab allocator cannot satisfy.
The SSE copy path requires the source and destination addresses to be 16-byte aligned; klalloc returns suitably aligned memory.