VESA BIOS Extensions

VBE is a compatibility interface for discovering and setting graphics modes. lcom-ng exposes a VBE-shaped API so you can practice the same flow without needing BIOS calls from a VM.

A typical graphics setup asks for mode information, chooses a supported mode, requests a linear framebuffer, maps the framebuffer, draws into it, and presents the result. The exact function names are course-specific, but the order is the important part. Drawing before a mode is selected or before memory is mapped is not meaningful.

Mode Information

Mode information tells you the horizontal resolution, vertical resolution, bits per pixel, pitch, and framebuffer address. Treat this structure as the source of truth for drawing helpers. A rectangle function should not silently assume a hardcoded width just because the first test happens to use a familiar mode.

The linear framebuffer flag also matters. It asks the device to expose the frame as a flat memory region rather than an older banked model. Banked graphics are historically interesting, but the linear model is the right teaching target for this course because it lets the rest of the lab focus on address calculation and clipping.

IMPORTANT

Do not hardcode mode dimensions in drawing helpers. Use the mode information returned by the runtime.

Indexed colors

Mode 0x105 uses the course's default 16 VGA colors at indices 0 through 15. Index 4 is dark red and index 14 is yellow. Indices 16 through 255 currently render as grayscale. Custom VGA DAC palette programming is not supported. Use a direct color mode for sprites that need a full RGB palette.