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display: layer client API + the display-demo client (D4)

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Drive the compositor from a separate process, proving the pipeline end to end.

- runtime.display: a Layer handle (fill / blitTile / configure / damage /
  destroy), createLayer, and a color(r,g,b) helper that caches the mode and
  packs via protocol.pack. Coordinates are signed over the u32 wire fields
  (@bitCast both ways), so a layer may sit or move partly off-screen.
- system/services/display-demo: the input-source analog for the compositor — a
  full-screen wallpaper, a rectangle it slides back and forth (moved by
  configure each frame, so the damage-driven present repaints old + new), and a
  cursor. Presents in a loop paced by runtime.time. Wired into build + initrd.

Fix this surfaced: protocol.message_maximum was 4096, but the kernel caps every
IPC message at MESSAGE_MAXIMUM = 256, so replyWait rejected the oversized receive
buffer with -E2BIG and the serve loop had been spinning since D2 (invisibly, as
those gates matched init-time heartbeats). Set it to 256; blit_tile is now
explicitly a small-tile path (larger bitmaps are the deferred shm surface).

Gate: `python3 test/qemu_test.py display-demo` — the demo drives frames of
motion through the layer client API and logs `display-demo: ok`. Regression:
zig build test, display (D1), display-service (D2/D3), and default zig build.
This commit is contained in:
Daniel Samson
2026-07-14 01:56:37 +01:00
parent f9cf0007c5
commit 105203b447
8 changed files with 253 additions and 17 deletions
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build.zig
+3
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@@ -467,6 +467,7 @@ pub fn build(b: *std.Build) void {
// at /mnt/usb. Its engine (engine.zig / on-disk.zig) is imported relatively.
const fat_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "fat", "system/services/fat/fat.zig");
const display_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "display", "system/services/display/display.zig");
const display_demo_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "display-demo", "system/services/display-demo/display-demo.zig");
const fat_test_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "fat-test", "system/services/fat/fat-test.zig");
const pci_bus_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "pci-bus", "system/drivers/pci-bus/pci-bus.zig");
// The PCI bus driver decodes each function's class triple to human names in its
@@ -536,6 +537,8 @@ pub fn build(b: *std.Build) void {
mk_run.addFileArg(fat_test_exe.getEmittedBin());
mk_run.addArg("display");
mk_run.addFileArg(display_exe.getEmittedBin());
mk_run.addArg("display-demo");
mk_run.addFileArg(display_demo_exe.getEmittedBin());
mk_run.addArg("pci-bus");
mk_run.addFileArg(pci_bus_exe.getEmittedBin());
mk_run.addArg("crash-test");