From 5cc0a5fd73d854c7fa528fd88a2f8303b1ad5e08 Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Sun, 28 Jan 2018 11:01:44 -0500
Subject: Add fb.c

---
 bin/fb.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 bin/fb.c

diff --git a/bin/fb.c b/bin/fb.c
new file mode 100644
index 00000000..985ba3b4
--- /dev/null
+++ b/bin/fb.c
@@ -0,0 +1,88 @@
+#include <assert.h>
+#include <err.h>
+#include <fcntl.h>
+#include <linux/fb.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sysexits.h>
+#include <termios.h>
+#include <unistd.h>
+
+extern void draw(uint32_t *buf, uint32_t xres, uint32_t yres);
+extern void input(char c);
+
+static uint32_t size;
+static uint32_t *buf;
+static uint32_t *saveBuf;
+
+static void restoreBuf(void) {
+    memcpy(buf, saveBuf, size);
+}
+
+static struct termios saveTerm;
+
+static void restoreTerm(void) {
+    tcsetattr(STDERR_FILENO, TCSADRAIN, &saveTerm);
+}
+
+int main() {
+    int error;
+
+    char *path = getenv("FRAMEBUFFER");
+    if (!path) path = "/dev/fb0";
+
+    int fd = open(path, O_RDWR);
+    if (fd < 0) err(EX_OSFILE, "%s", path);
+
+    struct fb_fix_screeninfo fix;
+    error = ioctl(fd, FBIOGET_FSCREENINFO, &fix);
+    if (error) err(EX_IOERR, "%s", path);
+
+    struct fb_var_screeninfo var;
+    error = ioctl(fd, FBIOGET_VSCREENINFO, &var);
+    if (error) err(EX_IOERR, "%s", path);
+
+    assert(!var.xoffset);
+    assert(!var.yoffset);
+    assert(var.bits_per_pixel == 32);
+    assert(!var.grayscale);
+    assert(var.red.offset == 16);
+    assert(var.red.length == 8);
+    assert(var.green.offset == 8);
+    assert(var.green.length == 8);
+    assert(var.blue.offset == 0);
+    assert(var.blue.length == 8);
+    assert(fix.line_length == var.xres * 4);
+
+    size = var.xres * var.yres * 4;
+    buf = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (buf == MAP_FAILED) err(EX_OSERR, "%s", path);
+
+    saveBuf = malloc(size);
+    if (!saveBuf) err(EX_OSERR, "malloc");
+    memcpy(saveBuf, buf, size);
+    atexit(restoreBuf);
+
+    error = tcgetattr(STDERR_FILENO, &saveTerm);
+    if (error) err(EX_IOERR, "tcgetattr");
+    atexit(restoreTerm);
+
+    struct termios raw;
+    cfmakeraw(&raw);
+    error = tcsetattr(STDERR_FILENO, TCSADRAIN, &raw);
+    if (error) err(EX_IOERR, "tcsetattr");
+
+    for (;;) {
+        draw(buf, var.xres, var.yres);
+
+        char c;
+        ssize_t len = read(STDIN_FILENO, &c, 1);
+        if (len < 0) err(EX_IOERR, "read");
+        if (!len || c == CTRL('C')) return EX_OK;
+
+        input(c);
+    }
+}
-- 
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