Graphics Demo

Overview

The Graphics Demo is a UEFI application that uses the Graphics Output Protocol (GOP) to switch graphics modes and render directly into the framebuffer.

Unlike previous applications that only used text console output, this application performs pixel-level graphics rendering before an operating system is loaded.

Goal

The goal of this application is to understand how UEFI exposes graphics hardware through GOP and how firmware applications can draw directly into video memory.

What it demonstrates

Locating EFI_GRAPHICS_OUTPUT_PROTOCOL
Querying available graphics modes
Switching modes using SetMode()
Accessing framebuffer memory
Plotting individual pixels
Drawing lines and rectangles
Separating console output from graphical rendering

GOP Workflow

The application follows this sequence:

    LocateProtocol()
            |
            v
    EFI_GRAPHICS_OUTPUT_PROTOCOL
            |
            v
    QueryMode()
            |
            v
    SetMode()
            |
            v
    Access framebuffer
            |
            v
    Render pixels and shapes

Framebuffer Rendering

After selecting a graphics mode, GOP provides:

Framebuffer base address
Framebuffer size
Resolution
Pixel format
Pixels-per-scan-line information

Rendering is performed by writing pixel values directly into framebuffer memory.

Drawing Primitives

The demo implements several basic rendering primitives:

PutPixel()
Horizontal lines
Vertical lines
Rectangle outlines
Filled rectangles

These primitives are sufficient to build simple user interfaces and debugging overlays.

Console vs Graphics

A useful observation is that text console output and framebuffer rendering are not the same subsystem.

The application reserves a region of the screen for graphics rendering while keeping console messages visible in another area.

This demonstrates the separation between:

UEFI text console services
GOP framebuffer rendering

Memory Ownership

An important detail discovered during development concerns QueryMode().

The function returns a buffer allocated by the graphics driver.

This means the caller must release the memory with FreePool() after the mode information is no longer needed.

This differs from APIs such as GetMemoryMap(), where the caller allocates the buffer itself.

Output

Example framebuffer rendering:

Graphics Output Demo

The demo draws colored rectangles and lines directly into video memory while running inside QEMU with OVMF firmware.

Next Steps

The next stage of the project moves from standalone applications to boot loader development.

Boot Loader Overview