63 lines
1.8 KiB
Plaintext
63 lines
1.8 KiB
Plaintext
.TH FRAMEBUFFER 2
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.SH NAME
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fb_info, fb_map - direct framebuffer access
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.SH SYNOPSIS
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.BI void montauk::fb_info(montauk::abi::FbInfo* info);
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.BI void* montauk::fb_map();
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.SH DESCRIPTION
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These syscalls allow userspace programs to access the linear
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framebuffer directly for graphical output.
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.SS fb_info
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Fills in an FbInfo structure with the framebuffer geometry:
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montauk::abi::FbInfo fb;
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montauk::fb_info(&fb);
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// fb.width, fb.height, fb.pitch, fb.bpp
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The pitch is the number of bytes per scanline (may be larger
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than width * 4 due to alignment). bpp is always 32.
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.SS fb_map
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Maps the physical framebuffer into the process address space at
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a fixed virtual address (0x50000000) and returns that address.
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uint32_t* pixels = (uint32_t*)montauk::fb_map();
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Each pixel is a 32-bit value in 0xAARRGGBB format (blue in the
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low byte). Writing to this memory directly updates the screen.
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.SH PIXEL FORMAT
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Bits 31-24: Alpha (unused, typically 0xFF)
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Bits 23-16: Red
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Bits 15-8: Green
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Bits 7-0: Blue
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Example: red = 0x00FF0000, green = 0x0000FF00, blue = 0x000000FF
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.SH EXAMPLE
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Fill the screen with blue:
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montauk::abi::FbInfo fb;
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montauk::fb_info(&fb);
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uint32_t* pixels = (uint32_t*)montauk::fb_map();
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for (uint64_t y = 0; y < fb.height; y++) {
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uint32_t* row = (uint32_t*)((uint8_t*)pixels + y * fb.pitch);
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for (uint64_t x = 0; x < fb.width; x++) {
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row[x] = 0x000000FF;
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}
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}
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.SH NOTES
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After mapping, the cursor overlay is not composited. Programs
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that use the framebuffer take full control of screen output.
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Only one mapping per process is supported. Calling fb_map()
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multiple times returns the same address.
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.SH SEE ALSO
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syscalls(2), malloc(3)
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