feat: io: serial & console

kernel/CMakeLists.txt

@@ -19,6 +19,9 @@ target_include_directories(shitgui PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/include")
 add_executable(kernel 
     src/kmain.c
     src/modules/memory.c
+    src/modules/serial.c
+    src/modules/console.c
+    data/font8x8_basic.c
 )
 
 target_include_directories(kernel PRIVATE
@@ -43,4 +46,9 @@ set_target_properties(kernel PROPERTIES
 add_custom_command(TARGET kernel POST_BUILD
     COMMAND objcopy -O binary $<TARGET_FILE:kernel> $<TARGET_FILE_DIR:kernel>/kernel.bin
     COMMENT "Stripping ELF headers -> kernel.bin"
+)
+
+file(GLOB_RECURSE SOURCES 
+    "src/*.c"
+    "data/*.c"
 )

kernel/data/font8x8_basic.c

@@ -0,0 +1,152 @@
+/**
+ * 8x8 monochrome bitmap fonts for rendering
+ * Author: Daniel Hepper <daniel@hepper.net>
+ *
+ * License: Public Domain
+ *
+ * Based on:
+ * // Summary: font8x8.h
+ * // 8x8 monochrome bitmap fonts for rendering
+ * //
+ * // Author:
+ * //     Marcel Sondaar
+ * //     International Business Machines (public domain VGA fonts)
+ * //
+ * // License:
+ * //     Public Domain
+ *
+ * Fetched from: http://dimensionalrift.homelinux.net/combuster/mos3/?p=viewsource&file=/modules/gfx/font8_8.asm
+ **/
+
+// Constant: font8x8_basic
+// Contains an 8x8 font map for unicode points U+0000 - U+007F (basic latin)
+char font8x8_basic[128][8] = {
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0000 (nul)
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0001
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0002
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0003
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0004
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0005
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0006
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0007
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0008
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0009
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+000A
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+000B
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+000C
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+000D
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+000E
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+000F
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0010
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0011
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0012
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0013
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0014
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0015
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0016
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0017
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0018
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0019
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+001A
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+001B
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+001C
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+001D
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+001E
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+001F
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0020 (space)
+    { 0x18, 0x3C, 0x3C, 0x18, 0x18, 0x00, 0x18, 0x00},   // U+0021 (!)
+    { 0x36, 0x36, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0022 (")
+    { 0x36, 0x36, 0x7F, 0x36, 0x7F, 0x36, 0x36, 0x00},   // U+0023 (#)
+    { 0x0C, 0x3E, 0x03, 0x1E, 0x30, 0x1F, 0x0C, 0x00},   // U+0024 ($)
+    { 0x00, 0x63, 0x33, 0x18, 0x0C, 0x66, 0x63, 0x00},   // U+0025 (%)
+    { 0x1C, 0x36, 0x1C, 0x6E, 0x3B, 0x33, 0x6E, 0x00},   // U+0026 (&)
+    { 0x06, 0x06, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0027 (')
+    { 0x18, 0x0C, 0x06, 0x06, 0x06, 0x0C, 0x18, 0x00},   // U+0028 (()
+    { 0x06, 0x0C, 0x18, 0x18, 0x18, 0x0C, 0x06, 0x00},   // U+0029 ())
+    { 0x00, 0x66, 0x3C, 0xFF, 0x3C, 0x66, 0x00, 0x00},   // U+002A (*)
+    { 0x00, 0x0C, 0x0C, 0x3F, 0x0C, 0x0C, 0x00, 0x00},   // U+002B (+)
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x0C, 0x0C, 0x06},   // U+002C (,)
+    { 0x00, 0x00, 0x00, 0x3F, 0x00, 0x00, 0x00, 0x00},   // U+002D (-)
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x0C, 0x0C, 0x00},   // U+002E (.)
+    { 0x60, 0x30, 0x18, 0x0C, 0x06, 0x03, 0x01, 0x00},   // U+002F (/)
+    { 0x3E, 0x63, 0x73, 0x7B, 0x6F, 0x67, 0x3E, 0x00},   // U+0030 (0)
+    { 0x0C, 0x0E, 0x0C, 0x0C, 0x0C, 0x0C, 0x3F, 0x00},   // U+0031 (1)
+    { 0x1E, 0x33, 0x30, 0x1C, 0x06, 0x33, 0x3F, 0x00},   // U+0032 (2)
+    { 0x1E, 0x33, 0x30, 0x1C, 0x30, 0x33, 0x1E, 0x00},   // U+0033 (3)
+    { 0x38, 0x3C, 0x36, 0x33, 0x7F, 0x30, 0x78, 0x00},   // U+0034 (4)
+    { 0x3F, 0x03, 0x1F, 0x30, 0x30, 0x33, 0x1E, 0x00},   // U+0035 (5)
+    { 0x1C, 0x06, 0x03, 0x1F, 0x33, 0x33, 0x1E, 0x00},   // U+0036 (6)
+    { 0x3F, 0x33, 0x30, 0x18, 0x0C, 0x0C, 0x0C, 0x00},   // U+0037 (7)
+    { 0x1E, 0x33, 0x33, 0x1E, 0x33, 0x33, 0x1E, 0x00},   // U+0038 (8)
+    { 0x1E, 0x33, 0x33, 0x3E, 0x30, 0x18, 0x0E, 0x00},   // U+0039 (9)
+    { 0x00, 0x0C, 0x0C, 0x00, 0x00, 0x0C, 0x0C, 0x00},   // U+003A (:)
+    { 0x00, 0x0C, 0x0C, 0x00, 0x00, 0x0C, 0x0C, 0x06},   // U+003B (;)
+    { 0x18, 0x0C, 0x06, 0x03, 0x06, 0x0C, 0x18, 0x00},   // U+003C (<)
+    { 0x00, 0x00, 0x3F, 0x00, 0x00, 0x3F, 0x00, 0x00},   // U+003D (=)
+    { 0x06, 0x0C, 0x18, 0x30, 0x18, 0x0C, 0x06, 0x00},   // U+003E (>)
+    { 0x1E, 0x33, 0x30, 0x18, 0x0C, 0x00, 0x0C, 0x00},   // U+003F (?)
+    { 0x3E, 0x63, 0x7B, 0x7B, 0x7B, 0x03, 0x1E, 0x00},   // U+0040 (@)
+    { 0x0C, 0x1E, 0x33, 0x33, 0x3F, 0x33, 0x33, 0x00},   // U+0041 (A)
+    { 0x3F, 0x66, 0x66, 0x3E, 0x66, 0x66, 0x3F, 0x00},   // U+0042 (B)
+    { 0x3C, 0x66, 0x03, 0x03, 0x03, 0x66, 0x3C, 0x00},   // U+0043 (C)
+    { 0x1F, 0x36, 0x66, 0x66, 0x66, 0x36, 0x1F, 0x00},   // U+0044 (D)
+    { 0x7F, 0x46, 0x16, 0x1E, 0x16, 0x46, 0x7F, 0x00},   // U+0045 (E)
+    { 0x7F, 0x46, 0x16, 0x1E, 0x16, 0x06, 0x0F, 0x00},   // U+0046 (F)
+    { 0x3C, 0x66, 0x03, 0x03, 0x73, 0x66, 0x7C, 0x00},   // U+0047 (G)
+    { 0x33, 0x33, 0x33, 0x3F, 0x33, 0x33, 0x33, 0x00},   // U+0048 (H)
+    { 0x1E, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x1E, 0x00},   // U+0049 (I)
+    { 0x78, 0x30, 0x30, 0x30, 0x33, 0x33, 0x1E, 0x00},   // U+004A (J)
+    { 0x67, 0x66, 0x36, 0x1E, 0x36, 0x66, 0x67, 0x00},   // U+004B (K)
+    { 0x0F, 0x06, 0x06, 0x06, 0x46, 0x66, 0x7F, 0x00},   // U+004C (L)
+    { 0x63, 0x77, 0x7F, 0x7F, 0x6B, 0x63, 0x63, 0x00},   // U+004D (M)
+    { 0x63, 0x67, 0x6F, 0x7B, 0x73, 0x63, 0x63, 0x00},   // U+004E (N)
+    { 0x1C, 0x36, 0x63, 0x63, 0x63, 0x36, 0x1C, 0x00},   // U+004F (O)
+    { 0x3F, 0x66, 0x66, 0x3E, 0x06, 0x06, 0x0F, 0x00},   // U+0050 (P)
+    { 0x1E, 0x33, 0x33, 0x33, 0x3B, 0x1E, 0x38, 0x00},   // U+0051 (Q)
+    { 0x3F, 0x66, 0x66, 0x3E, 0x36, 0x66, 0x67, 0x00},   // U+0052 (R)
+    { 0x1E, 0x33, 0x07, 0x0E, 0x38, 0x33, 0x1E, 0x00},   // U+0053 (S)
+    { 0x3F, 0x2D, 0x0C, 0x0C, 0x0C, 0x0C, 0x1E, 0x00},   // U+0054 (T)
+    { 0x33, 0x33, 0x33, 0x33, 0x33, 0x33, 0x3F, 0x00},   // U+0055 (U)
+    { 0x33, 0x33, 0x33, 0x33, 0x33, 0x1E, 0x0C, 0x00},   // U+0056 (V)
+    { 0x63, 0x63, 0x63, 0x6B, 0x7F, 0x77, 0x63, 0x00},   // U+0057 (W)
+    { 0x63, 0x63, 0x36, 0x1C, 0x1C, 0x36, 0x63, 0x00},   // U+0058 (X)
+    { 0x33, 0x33, 0x33, 0x1E, 0x0C, 0x0C, 0x1E, 0x00},   // U+0059 (Y)
+    { 0x7F, 0x63, 0x31, 0x18, 0x4C, 0x66, 0x7F, 0x00},   // U+005A (Z)
+    { 0x1E, 0x06, 0x06, 0x06, 0x06, 0x06, 0x1E, 0x00},   // U+005B ([)
+    { 0x03, 0x06, 0x0C, 0x18, 0x30, 0x60, 0x40, 0x00},   // U+005C (\)
+    { 0x1E, 0x18, 0x18, 0x18, 0x18, 0x18, 0x1E, 0x00},   // U+005D (])
+    { 0x08, 0x1C, 0x36, 0x63, 0x00, 0x00, 0x00, 0x00},   // U+005E (^)
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF},   // U+005F (_)
+    { 0x0C, 0x0C, 0x18, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+0060 (`)
+    { 0x00, 0x00, 0x1E, 0x30, 0x3E, 0x33, 0x6E, 0x00},   // U+0061 (a)
+    { 0x07, 0x06, 0x06, 0x3E, 0x66, 0x66, 0x3B, 0x00},   // U+0062 (b)
+    { 0x00, 0x00, 0x1E, 0x33, 0x03, 0x33, 0x1E, 0x00},   // U+0063 (c)
+    { 0x38, 0x30, 0x30, 0x3e, 0x33, 0x33, 0x6E, 0x00},   // U+0064 (d)
+    { 0x00, 0x00, 0x1E, 0x33, 0x3f, 0x03, 0x1E, 0x00},   // U+0065 (e)
+    { 0x1C, 0x36, 0x06, 0x0f, 0x06, 0x06, 0x0F, 0x00},   // U+0066 (f)
+    { 0x00, 0x00, 0x6E, 0x33, 0x33, 0x3E, 0x30, 0x1F},   // U+0067 (g)
+    { 0x07, 0x06, 0x36, 0x6E, 0x66, 0x66, 0x67, 0x00},   // U+0068 (h)
+    { 0x0C, 0x00, 0x0E, 0x0C, 0x0C, 0x0C, 0x1E, 0x00},   // U+0069 (i)
+    { 0x30, 0x00, 0x30, 0x30, 0x30, 0x33, 0x33, 0x1E},   // U+006A (j)
+    { 0x07, 0x06, 0x66, 0x36, 0x1E, 0x36, 0x67, 0x00},   // U+006B (k)
+    { 0x0E, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x1E, 0x00},   // U+006C (l)
+    { 0x00, 0x00, 0x33, 0x7F, 0x7F, 0x6B, 0x63, 0x00},   // U+006D (m)
+    { 0x00, 0x00, 0x1F, 0x33, 0x33, 0x33, 0x33, 0x00},   // U+006E (n)
+    { 0x00, 0x00, 0x1E, 0x33, 0x33, 0x33, 0x1E, 0x00},   // U+006F (o)
+    { 0x00, 0x00, 0x3B, 0x66, 0x66, 0x3E, 0x06, 0x0F},   // U+0070 (p)
+    { 0x00, 0x00, 0x6E, 0x33, 0x33, 0x3E, 0x30, 0x78},   // U+0071 (q)
+    { 0x00, 0x00, 0x3B, 0x6E, 0x66, 0x06, 0x0F, 0x00},   // U+0072 (r)
+    { 0x00, 0x00, 0x3E, 0x03, 0x1E, 0x30, 0x1F, 0x00},   // U+0073 (s)
+    { 0x08, 0x0C, 0x3E, 0x0C, 0x0C, 0x2C, 0x18, 0x00},   // U+0074 (t)
+    { 0x00, 0x00, 0x33, 0x33, 0x33, 0x33, 0x6E, 0x00},   // U+0075 (u)
+    { 0x00, 0x00, 0x33, 0x33, 0x33, 0x1E, 0x0C, 0x00},   // U+0076 (v)
+    { 0x00, 0x00, 0x63, 0x6B, 0x7F, 0x7F, 0x36, 0x00},   // U+0077 (w)
+    { 0x00, 0x00, 0x63, 0x36, 0x1C, 0x36, 0x63, 0x00},   // U+0078 (x)
+    { 0x00, 0x00, 0x33, 0x33, 0x33, 0x3E, 0x30, 0x1F},   // U+0079 (y)
+    { 0x00, 0x00, 0x3F, 0x19, 0x0C, 0x26, 0x3F, 0x00},   // U+007A (z)
+    { 0x38, 0x0C, 0x0C, 0x07, 0x0C, 0x0C, 0x38, 0x00},   // U+007B ({)
+    { 0x18, 0x18, 0x18, 0x00, 0x18, 0x18, 0x18, 0x00},   // U+007C (|)
+    { 0x07, 0x0C, 0x0C, 0x38, 0x0C, 0x0C, 0x07, 0x00},   // U+007D (})
+    { 0x6E, 0x3B, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},   // U+007E (~)
+    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}    // U+007F
+};

kernel/include/console.h

@@ -0,0 +1,10 @@
+#ifndef CONSOLE_H
+#define CONSOLE_H
+
+#include "shitgui.h"
+
+void console_init(SG_Context *ctx);
+void console_set_color(u32 color);
+void kprint(const char *str);
+
+#endif

kernel/include/font.h

@@ -0,0 +1,8 @@
+#ifndef FONT_H
+#define FONT_H
+
+#include "types.h"
+
+extern u8 font8x8_basic[128][8];
+
+#endif

kernel/include/io.h

@@ -0,0 +1,18 @@
+static inline void outb(unsigned short port, unsigned char val) {
+    __asm__ volatile( 
+        "outb %0, %1" 
+        : 
+        : "a"(val), 
+        "Nd"(port) );
+}
+
+static inline unsigned char inb(unsigned short port) {
+    unsigned char ret;
+    __asm__ volatile(
+        "inb %1, %0"
+        : "=a"(ret)
+        : "Nd"(port)
+    );
+
+    return ret;
+}

kernel/include/serial.h

@@ -0,0 +1,8 @@
+#ifndef SERIAL_H
+#define SERIAL_H
+
+int serial_init();
+void serial_writec(char chr);
+void serial_write(const char *str);
+
+#endif

kernel/include/shitgui.h

@@ -20,11 +20,13 @@ typedef struct {
 } SG_Image;
 
 typedef struct {
-    u32 font_w;
+    u32 w;
-    u32 font_h;
+    u32 h;
-} SG_FontMetrics;
+    const unsigned char* base;
+} SG_Font;
 
 void sg_put_img(SG_Context *ctx, SG_Point *p, SG_Image *img);
 void sg_draw_rect(SG_Context *ctx, SG_Point *p, u32 w, u32 h, u32 color);
+void sg_draw_char_bitmap(SG_Context *ctx, SG_Point *p, char c, u32 color, SG_Font *font);
 
 #endif

kernel/src/kmain.c

@@ -1,7 +1,9 @@
 #include "../../common/bootinfo.h"
+#include "console.h"
 #include "types.h"
 
 #include "shitgui.h"
+#include "serial.h"
 
 void kmain(Bootinfo* info) {
     u32 *fb = (u32*)info->base;
@@ -29,5 +31,11 @@ void kmain(Bootinfo* info) {
     p.y += stripe_h;
     sg_draw_rect(&sg_ctx, &p, info->width, stripe_h, 0x5BCEFA);
 
+    serial_init();
+    console_init(&sg_ctx);
+    console_set_color(0x000000);
+    kprint("Hello!!!");
+    for (int i = 0; i < 1000; i++) kprint("!");
+
     while (1) { __asm__("hlt"); }
 }

kernel/src/modules/console.c

@@ -0,0 +1,44 @@
+#include "console.h"
+#include "serial.h"
+#include "font.h"
+#include "shitgui.h"
+
+static SG_Context *ctx_ptr = nullptr;
+static SG_Point s_cursor_pos = {0};
+static SG_Font s_font = {0};
+static u32 s_color = 0xFFFFFF;
+
+void console_init(SG_Context *ctx) {
+    ctx_ptr = ctx;
+    s_cursor_pos.x = 0;
+    s_cursor_pos.y = 0;
+
+    s_font.h = 8;
+    s_font.w = 8;
+    s_font.base = (const unsigned char*)font8x8_basic;
+}
+
+static void console_putc(char c) {
+    serial_writec(c);
+    if (!ctx_ptr) return;
+    if (c == '\n') {
+        s_cursor_pos.x = 0;
+        s_cursor_pos.y += s_font.h;
+    } else {
+        sg_draw_char_bitmap(ctx_ptr, &s_cursor_pos, c, s_color, &s_font);
+        s_cursor_pos.x += s_font.w;
+    }
+
+    if (s_cursor_pos.x >= ctx_ptr->width) {
+        s_cursor_pos.x = 0;
+        s_cursor_pos.y += s_font.h;
+    }
+}
+
+void console_set_color(u32 color) {
+    s_color = color;
+}
+
+void kprint(const char *str) {
+    for (int i = 0; str[i] != '\0'; i++) console_putc(str[i]);
+}

kernel/src/modules/memory.c

@@ -1,3 +1,4 @@
+#include "memory.h"
 #include "types.h"
 
 void *memset(void *ptr, int value, usize num) {

kernel/src/modules/serial.c

@@ -0,0 +1,28 @@
+#include "serial.h"
+#include "io.h"
+
+#define PORT 0x3F8 // com1
+
+int serial_init() {
+    outb(PORT + 1, 0x00); // interrupt enable register (+1) / disable interruptions
+    outb(PORT + 3, 0x80); // line control register (+3) 
+    outb(PORT + 0, 0x03); // speed : low byte
+    outb(PORT + 1, 0x00); // speed : high byte
+    outb(PORT + 3, 0x03); // line control register (+3) / reset DLAB / no parity / 1 stop bit / (8N1)
+    outb(PORT + 2, 0xC7); // FIFO Control register (+2) / 1100 0111 / last ones are enable FIFO buff / first ones to clean noise
+    outb(PORT + 4, 0x0B); // ready :3
+    return 0;
+}
+
+static int is_transmit_empty() { 
+    return inb(PORT + 5) & 0x20; // checking 5th bit LSR 
+}
+
+void serial_writec(char chr) {
+    while (is_transmit_empty() == 0); // waiting for buffer to flush (spinlock)
+    outb(PORT, chr);
+}
+
+void serial_write(const char *str) {
+    for (int i = 0; str[i] != '\0'; i++) serial_writec(str[i]);
+}

kernel/src/modules/shitgui.c

@@ -42,4 +42,27 @@ void sg_draw_rect(SG_Context *ctx, SG_Point *p, u32 w, u32 h, u32 color) {
         volatile u32 *row_ptr = &ctx->fb[(start_y + y) * ctx->pitch + start_x];
         for (u32 x = 0; x < draw_w; x++) row_ptr[x] = color;
     }
+}
+
+void sg_draw_char_bitmap(SG_Context *ctx, SG_Point *p, char c, u32 color, SG_Font *font) {
+    if (!ctx->fb) return;
+
+    u32 start_x = p->x;
+    u32 start_y = p->y;
+    u32 draw_w = font->w;
+    u32 draw_h = font->h;
+
+    if (start_x >= ctx->width || start_y >= ctx->height) return;
+    if (start_x + draw_w > ctx->width) draw_w = ctx->width - start_x;
+    if (start_y + draw_h > ctx->height) draw_h = ctx->height - start_y;
+
+    for (u32 y = 0; y < draw_h; y++) {
+        u8 bitmap_row = font->base[(unsigned char)c * font->h + y];
+        volatile u32 *row_ptr = &ctx->fb[(start_y + y) * ctx->pitch + start_x];
+        for (u32 x = 0; x < draw_w; x++) {
+            if (bitmap_row & (1 << (font->w - 1 - x))) {
+                row_ptr[x] = color;
+            }
+        }
+    }
 }