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boot: a shared UI, and a graphical splash on UEFI

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The first piece of the two loaders that is genuinely common code rather
than a contract they both honour. It can be, because the difference
between the firmwares is entirely in how a framebuffer is *obtained* --
VBE in real mode, or GOP -- and not in what you do with one afterwards.
boot/common/ui.c takes a base, a size and a stride and draws; it knows
nothing about disks, memory maps or mode setting, which is what lets it
compile into a 16/32/64-bit BIOS loader and a PE/COFF UEFI application
without either leaking into it.

The look is deliberately quiet: dark ground, the mark centred, one thin
bar beneath it, nothing on screen that is not load-bearing. The whole
group is laid out from the centre outwards rather than from the top down,
so it sits identically at 800x600 and at 1600x1200 instead of drifting up
the screen as the mode grows.

UEFI had no graphical splash at all -- it printed text to a console the
QEMU window is usually not even showing. It draws the same screen as the
BIOS path now, with the bar tracking bytes of kernel actually written
rather than a segment count, which says nothing about how long each takes.

Two ordering bugs found by looking at the pixels rather than the code:
setup_framebuffer ran *after* the kernel was read, so every progress tick
went to a framebuffer that did not exist yet and the splash then painted
over the result; and that also put the resolution prompt after the
slowest step instead of at the start. The display is set up first now.

Verified from the host with screendump: background is exactly SCH_BG, the
bar is 4px tall and width/4 wide at y=495 on a 1280x800 screen, which is
where centring the group puts it. UEFI still boots to cpu0; BIOS
bootcheck 27/27.

Not yet shared: the BIOS loader still draws with its own copy of this
code. Deleting that copy in favour of this one is the next step and the
point of the exercise -- until then this is one loader using shared code
and one duplicating it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Nexoniarz 2026-08-10 22:26:54 +02:00
commit 64e4835524
4 changed files with 378 additions and 4 deletions
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6
Makefile
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@ -390,10 +390,12 @@ kernel: $(BUILD)/kernel/kernel
# -----------------------------------------------------------------------
UEFI_CFLAGS = --target=x86_64-unknown-windows -ffreestanding -fshort-wchar -mno-red-zone -fno-stack-protector -Wall -Wextra -O1 -I./include
$(BUILD)/uefi/BOOTX64.EFI: boot/uefi/main.c boot/uefi/efi.h include/schboot.h
$(BUILD)/uefi/BOOTX64.EFI: boot/uefi/main.c boot/uefi/efi.h include/schboot.h \
boot/common/ui.c boot/common/ui.h
@mkdir -p $(BUILD)/uefi
clang $(UEFI_CFLAGS) -c boot/uefi/main.c -o $(BUILD)/uefi/main.obj
lld-link -subsystem:efi_application -entry:EfiMain -nodefaultlib $(BUILD)/uefi/main.obj -out:$@
clang $(UEFI_CFLAGS) -c boot/common/ui.c -o $(BUILD)/uefi/ui.obj
lld-link -subsystem:efi_application -entry:EfiMain -nodefaultlib $(BUILD)/uefi/main.obj $(BUILD)/uefi/ui.obj -out:$@
uefi: $(BUILD)/uefi/BOOTX64.EFI