Graphics Output Protocol

GOP replaces legacy VESA BIOS extensions with a UEFI protocol that sets a framebuffer mode and returns a pointer to pixel memory. Locate EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID via LocateProtocol or the handle database, then call SetMode and QueryMode. For example, mode 0 might be 1024x768x32 with a linear framebuffer at a physical address stored in Mode->FrameBufferBase.

Drawing a pixel

c
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QueryMode: Enumerate horizontal/vertical resolution and pixel format
Blt: Optional block transfer for rectangles without manual stride math
PixelFormat: BGRR8 or RGBA8 depending on firmware
GOP stays available until ExitBootServices unless the driver marks otherwise

Mode enumeration

Call QueryMode for every index from zero to Mode->MaxMode - 1 before picking a resolution. Some firmware exposes 1024x768 and 1920x1080 with different pixel formats; treat PixelsPerScanLine as stride, not width. After ExitBootServices, GOP may disappear; kernels that need a framebuffer must copy mode info first. OVMF usually offers GOP on a PCI video device even without a full OS driver stack.

Why for this exercise

You will locate GOP, switch to a graphics mode, and write pixels to the framebuffer. This exercise requires using protocol function pointers instead of INT 0x10 or VGA register I/O.

Simulate UEFI GOP framebuffer access in C.

Requirements:

Define EFI_GRAPHICS_OUTPUT_MODE_INFORMATION structure
Define GOP framebuffer with simulated memory
Implement gop_set_mode(width, height, format)
Implement gop_put_pixel(x, y, r, g, b)
Implement gop_fill_rect(x, y, w, h, color)
Implement gop_draw_gradient()
Show framebuffer base address and size
Show pixel format details
Calculate pixel offsets correctly
Show pixels_per_scanline vs width difference

Test:

Show mode set
Show pixel drawn
Show rectangle filled
Show gradient drawn
Show framebuffer info

Graphics Output Protocol

Drawing a pixel

c
Loading…

QueryMode: Enumerate horizontal/vertical resolution and pixel format
Blt: Optional block transfer for rectangles without manual stride math
PixelFormat: BGRR8 or RGBA8 depending on firmware
GOP stays available until ExitBootServices unless the driver marks otherwise

Mode enumeration

Why for this exercise

You will locate GOP, switch to a graphics mode, and write pixels to the framebuffer. This exercise requires using protocol function pointers instead of INT 0x10 or VGA register I/O.

Simulate UEFI GOP framebuffer access in C.

Requirements:

Define EFI_GRAPHICS_OUTPUT_MODE_INFORMATION structure
Define GOP framebuffer with simulated memory
Implement gop_set_mode(width, height, format)
Implement gop_put_pixel(x, y, r, g, b)
Implement gop_fill_rect(x, y, w, h, color)
Implement gop_draw_gradient()
Show framebuffer base address and size
Show pixel format details
Calculate pixel offsets correctly
Show pixels_per_scanline vs width difference

Test:

Show mode set
Show pixel drawn
Show rectangle filled
Show gradient drawn
Show framebuffer info

Use UEFI Graphics Output Protocol (GOP)

Topic Overview

Graphics Output Protocol

Drawing a pixel

Mode enumeration

Why for this exercise

Implementation Task

Progressive Hints

Resources

Learn by building

Use UEFI Graphics Output Protocol (GOP)

Topic Overview

Graphics Output Protocol

Drawing a pixel

Mode enumeration

Why for this exercise

Implementation Task

Progressive Hints

Resources

Learn by building