feat: basic framebuffer

4 files changed, 90 insertions, 6 deletions

diff --git a/boot/boot.zig b/boot/boot.zig
index a7822af..2303409 100644
--- a/boot/boot.zig
+++ b/boot/boot.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const limine = @import("limine.zig");
 const serial = @import("serial.zig");
+const framebuffer = @import("framebuffer.zig");
 
 // We need a panic handler otherwise zig won't be happy,
 // std usually formats a message through std.Io.Writer which
@@ -9,9 +10,9 @@ const serial = @import("serial.zig");
 pub const panic = std.debug.FullPanic(struct {
     fn halt(msg: []const u8, _: ?usize) noreturn {
         serial.init();
-        serial.write("\n!!! uhhhh engine kaput : ");
+        serial.write("\r\n!!! uhhhh engine kaput : ");
         serial.write(msg);
-        serial.write("\n");
+        serial.write("\r\n");
         while (true) asm volatile ("hlt");
     }
 }.halt);
@@ -24,6 +25,22 @@ export var requests_end: limine.RequestsEndMarker linksection(".limine_requests_
 // ENTRY(_start)
 export fn _start() callconv(.c) noreturn {
     serial.init();
-    serial.write("if you see this, it means revel didn't shit the bed");
+    serial.write("if you see this, it means revel didn't shit the bed\r\n");
+
+    if (framebuffer.get()) |screen| {
+        // XOR texture
+        var y: usize = 0;
+        while (y < screen.height) : (y += 1) {
+            var x: usize = 0;
+            while (x < screen.width) : (x += 1) {
+                const v: u32 = @intCast((x ^ y) & 0xFF);
+                framebuffer.putpixel(screen, x, y, (v << 16) | (v << 8) | v);
+            }
+        }
+        serial.write("drew to the framebuffer\r\n");
+    } else {
+        serial.write("limine was a piece of shit.\r\n");
+    }
+
     while (true) asm volatile ("hlt");
 }
diff --git a/boot/framebuffer.zig b/boot/framebuffer.zig
new file mode 100644
index 0000000..6518b17
--- /dev/null
+++ b/boot/framebuffer.zig
@@ -0,0 +1,26 @@
+// linear framebuffer type shi you feel me?
+// see: https://wiki.osdev.org/Limine_Bare_Bones
+
+const limine = @import("limine.zig");
+
+pub const Framebuffer = limine.Framebuffer;
+
+// the request placed in .limine_requests so the loader finds and fills it
+// idk why this sounds vaguely erotic, like yeah fill me harder lol
+export var request: limine.FramebufferRequest linksection(".limine_requests") = .{};
+
+// the response pointer is written by Limine before we run, so read it through a
+// volatile pointer or the optimizer assumes it's still null
+pub fn get() ?*Framebuffer {
+    const req: *volatile limine.FramebufferRequest = &request;
+    const resp = req.response orelse return null;
+    if (resp.framebuffer_count == 0) return null;
+    return resp.framebuffers.?[0];
+}
+
+// assumes the usual Limine RGB 32-bpp layout im sure i wont forget about this layout
+// later and i wont fuck me over
+pub fn putpixel(fb: *Framebuffer, x: usize, y: usize, color: u32) void {
+    const pixel: *align(1) u32 = @ptrCast(fb.address + y * fb.pitch + x * 4);
+    pixel.* = color;
+}
diff --git a/boot/limine.zig b/boot/limine.zig
index e9aac9c..ef08867 100644
--- a/boot/limine.zig
+++ b/boot/limine.zig
@@ -25,3 +25,44 @@ pub const RequestsEndMarker = extern struct {
     m0: u64 = 0xadc0e0531bb10d03,
     m1: u64 = 0x9572709f31764c62,
 };
+
+// Every request id starts with this common magic, then two request-specific
+// words. Limine scans .limine_requests for these and fills in `response`.
+fn requestId(a: u64, b: u64) [4]u64 {
+    return .{ 0xc7b1dd30df4c8b88, 0x0a82e883a194f07b, a, b };
+}
+
+// --- Framebuffer feature: ask Limine for a linear framebuffer ---
+
+pub const Framebuffer = extern struct {
+    address: [*]u8,
+    width: u64,
+    height: u64,
+    pitch: u64, // bytes per row (not always width*bpp/8)
+    bpp: u16, // bits per pixel
+    memory_model: u8, // 1 = RGB
+    red_mask_size: u8,
+    red_mask_shift: u8,
+    green_mask_size: u8,
+    green_mask_shift: u8,
+    blue_mask_size: u8,
+    blue_mask_shift: u8,
+    // 7 bytes of padding land here (extern-struct alignment before edid_size)
+    edid_size: u64,
+    edid: ?*anyopaque,
+    // response revision 1 and up — unused for now:
+    mode_count: u64,
+    modes: ?*anyopaque,
+};
+
+pub const FramebufferResponse = extern struct {
+    revision: u64,
+    framebuffer_count: u64,
+    framebuffers: ?[*]*Framebuffer,
+};
+
+pub const FramebufferRequest = extern struct {
+    id: [4]u64 = requestId(0x9d5827dcd881dd75, 0xa3148604f6fab11b),
+    revision: u64 = 0,
+    response: ?*FramebufferResponse = null,
+};
diff --git a/boot/serial.zig b/boot/serial.zig
index cd6bd13..4863864 100644
--- a/boot/serial.zig
+++ b/boot/serial.zig
@@ -1,6 +1,6 @@
-// This is a minimal 16550 UART driver for COM1, this is 
-// mainly going to be used for debugging since its really 
-// simple to setup. Fun fact: i was drunk when i wrote this 
+// This is a minimal 16550 UART driver for COM1, this is mainly going 
+// to be used for debugging since its really simple to setup. 
+// Fun fact: i was drunk when i wrote this 
 //
 // see: https://wiki.osdev.org/Serial_Ports