From be4240d597716b2f4d3e3d0fbadfc8f219787ed1 Mon Sep 17 00:00:00 2001
From: "hunter@kvog.sh" <hunter@kvog.sh>
Date: Sun, 8 Feb 2026 09:21:46 -0600
Subject: rl: Basic framebuffer

---
 rushmore-linux/rlwsd/rlwsd.c | 77 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 73 insertions(+), 4 deletions(-)

(limited to 'rushmore-linux/rlwsd')

diff --git a/rushmore-linux/rlwsd/rlwsd.c b/rushmore-linux/rlwsd/rlwsd.c
index 0c96881..548dc9a 100644
--- a/rushmore-linux/rlwsd/rlwsd.c
+++ b/rushmore-linux/rlwsd/rlwsd.c
@@ -1,10 +1,15 @@
 #include <errno.h>
 #include <fcntl.h>
-// #include <linux/fb.h>
+#include <linux/fb.h>
+#include <linux/kd.h>
 #include <stdarg.h>
 #include <string.h>
+#include <stdint.h>
 #include <stdio.h>
+#include <sys/mman.h>
+#include <sys/ioctl.h>
 #include <sys/uio.h>
+#include <time.h>
 #include <unistd.h>
 
 static const char* tmp_fmt(const char* fmt, ...)
@@ -46,10 +51,74 @@ int main(void)
         panic(tmp_fmt("Failed to open /dev/fb0: %s", strerror(errno)));
     }
 
-    const char* msg = "[rlwsd] HELLO!\n";
-    write(1, msg, __builtin_strlen(msg));
+    struct fb_fix_screeninfo finfo;
+    struct fb_var_screeninfo vinfo;
+    if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) != 0) {
+        panic(tmp_fmt("FBIOGET_FSCREENINFO: %s", strerror(errno)));
+    }
+    if (ioctl(fd, FBIOGET_VSCREENINFO, &vinfo) != 0) {
+        panic(tmp_fmt("FBIOGET_VSCREENINFO: %s", strerror(errno)));
+    }
+
+    spew(tmp_fmt("fb0: %ux%u bpp=%u line_length=%u visual=%u",
+        vinfo.xres, vinfo.yres, vinfo.bits_per_pixel,
+        finfo.line_length, finfo.visual));
+    spew(tmp_fmt("fb0: R %u/%u G %u/%u B %u/%u",
+        vinfo.red.offset, vinfo.red.length,
+        vinfo.green.offset, vinfo.green.length,
+        vinfo.blue.offset, vinfo.blue.length));
+
+    if (vinfo.bits_per_pixel != 24) {
+        panic("BPP must be 24");
+    }
+
+    // Disable TTY
+    int tty = open("/dev/tty0", O_RDWR);
+    if (tty < 0) {
+        tty = open("/dev/console", O_RDWR);
+        if (tty < 0) {
+            panic(tmp_fmt("Couldn't open tty: %s", strerror(errno)));
+        }
+    }
+    if (ioctl(tty, KDSETMODE, KD_GRAPHICS) != 0) {
+        panic(tmp_fmt("Failed to set tty mode to KD_GRAPHICS: %s", strerror(errno)));
+    }
+    close(tty);
+
+    size_t fb_size = (size_t)finfo.line_length * vinfo.yres;
+    uint8_t* fb = (uint8_t*)mmap(NULL, fb_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (fb == MAP_FAILED) {
+        panic(tmp_fmt("mmap failed: %s", strerror(errno)));
+    }
+
+#if 1
+    for (uint32_t y = 0; y < vinfo.yres; ++y) {
+        uint8_t* row = fb + (size_t)y * finfo.line_length;
+        memset(row, 0x00, finfo.line_length);
+    }
+#endif
+
+    uint8_t lum = 0;
+    uint32_t y = 0;
+    float then = 0.0f;
+
     for (;;)
     {
-        pause();
+        struct timespec ts;
+        clock_gettime(CLOCK_MONOTONIC, &ts);
+        float now = ts.tv_sec + (ts.tv_nsec / 1e9f);
+        if ((now - then) >= (1.0f / 60.0f)) {
+            then = now;
+
+            uint32_t color = (uint32_t)lum << 24 | (uint32_t)lum << 16 | (uint32_t)lum << 8 | lum;
+            uint8_t* row = fb + (size_t)y * finfo.line_length;
+            for (size_t x = 0; x < vinfo.xres; ++x) {
+                size_t bpp = vinfo.bits_per_pixel / 8;
+                memcpy(&row[(x * bpp) + x], &color, 4);
+            }
+
+            lum = (lum + 7) % 255;
+            y = (y + 1) % (vinfo.yres - 1);
+        }
     }
 }
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