Add message overlay support

Makefile

@@ -46,6 +46,7 @@ SRC_SRCS_1 += cart.c mapper.c
 SRC_SRCS_1 += apu.c audio.c
 SRC_SRCS_1 += file.c save.c
 SRC_SRCS_1 += sdl_render.c sdl_input.c sdl_audio.c sdl_timer.c
+SRC_SRCS_1 += overlay.c sdl_overlay.c
 
 PLAT_SRCS_1 = filemap.c
 

src/charbits.h

@@ -0,0 +1,147 @@
+static const char chars[] = "\x7f!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`{|}~";
+
+static const int char_w = 10U;
+static const int char_h = 10U;
+static const int charbit_size = (1U + ((char_w * char_h * 2) + 7) / 8);
+static const int char_count = (sizeof(chars) - 1);
+
+static const uint8_t charbits[1794] = {
+    0x09, 0x55, 0x55, 0x90, 0xaa, 0x16, 0x59, 0x69, 0x91, 0xa5, 0x16, 0x99, 0x66,
+    0x91, 0x5a, 0x16, 0x69, 0x65, 0x91, 0xaa, 0x16, 0x55, 0x55, 0x41, 0x55, 0x15,
+    0x07, 0x50, 0x05, 0x00, 0x69, 0x01, 0x94, 0x16, 0x40, 0x6a, 0x01, 0xa4, 0x15,
+    0x40, 0x5a, 0x01, 0x55, 0x05, 0x90, 0x56, 0x00, 0x55, 0x01, 0x40, 0x15, 0x00,
+    0x08, 0x55, 0x15, 0x90, 0xa6, 0x05, 0x69, 0x5a, 0x90, 0xa6, 0x05, 0x55, 0x55,
+    0x40, 0x55, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x0a, 0x54, 0x55, 0x40, 0x9a, 0x16, 0xa5, 0x69, 0x91, 0xaa, 0x5a, 0xa5, 0x69,
+    0x95, 0xaa, 0x5a, 0xa5, 0x69, 0x45, 0x9a, 0x56, 0x54, 0x55, 0x01, 0x55, 0x15,
+    0x09, 0x50, 0x05, 0x40, 0x69, 0x05, 0xa5, 0x6a, 0x91, 0x56, 0x15, 0xa5, 0x5a,
+    0x51, 0x95, 0x16, 0xa9, 0x5a, 0x51, 0x69, 0x15, 0x54, 0x55, 0x00, 0x55, 0x01,
+    0x0a, 0x00, 0x00, 0x50, 0x45, 0x15, 0x69, 0xa5, 0x95, 0x96, 0x56, 0x55, 0x5a,
+    0x45, 0x69, 0x15, 0xa5, 0xa5, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x0a, 0x50, 0x15, 0x40, 0xa9, 0x05, 0xa4, 0x69, 0x41, 0x9a, 0x16, 0xa5, 0x5a,
+    0x91, 0x96, 0x5a, 0x69, 0x6a, 0x55, 0x6a, 0x5a, 0x54, 0x55, 0x05, 0x55, 0x55,
+    0x05, 0x55, 0x00, 0x90, 0x16, 0x00, 0x69, 0x01, 0x90, 0x16, 0x00, 0x55, 0x01,
+    0x40, 0x15, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x06, 0x54, 0x01, 0x50, 0x5a, 0x00, 0x69, 0x05, 0x90, 0x56, 0x00, 0x69, 0x01,
+    0x90, 0x16, 0x00, 0x69, 0x01, 0x50, 0x5a, 0x00, 0x54, 0x05, 0x00, 0x55, 0x00,
+    0x06, 0x55, 0x00, 0x90, 0x16, 0x00, 0xa5, 0x05, 0x40, 0x5a, 0x00, 0xa4, 0x05,
+    0x40, 0x5a, 0x00, 0xa5, 0x05, 0x90, 0x56, 0x00, 0x55, 0x01, 0x40, 0x05, 0x00,
+    0x0a, 0x00, 0x00, 0x40, 0x55, 0x05, 0xa4, 0x69, 0x51, 0xa9, 0x15, 0xa9, 0xaa,
+    0x55, 0xa9, 0x55, 0xa4, 0x69, 0x45, 0x55, 0x15, 0x50, 0x55, 0x01, 0x00, 0x00,
+    0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x54, 0x00, 0x50, 0x16, 0x00, 0xa9, 0x05,
+    0x50, 0x56, 0x00, 0x54, 0x05, 0x00, 0x15, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x54, 0x01,
+    0x40, 0x5a, 0x00, 0xa5, 0x05, 0x90, 0x56, 0x00, 0x55, 0x05, 0x40, 0x15, 0x00,
+    0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x50, 0x15, 0x00, 0xa9, 0x05,
+    0x50, 0x55, 0x00, 0x54, 0x05, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x40, 0x15, 0x00, 0xa4, 0x05, 0x40, 0x5a, 0x00, 0x54, 0x05, 0x00, 0x55, 0x00,
+    0x07, 0x50, 0x05, 0x00, 0x69, 0x01, 0x94, 0x16, 0x40, 0x5a, 0x01, 0xa4, 0x05,
+    0x50, 0x5a, 0x00, 0x69, 0x05, 0x90, 0x16, 0x00, 0x55, 0x01, 0x40, 0x15, 0x00,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x96, 0x5a, 0x69, 0xa6,
+    0x95, 0x5a, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x09, 0x50, 0x05, 0x40, 0x69, 0x01, 0xa4, 0x16, 0x40, 0x69, 0x01, 0x90, 0x16,
+    0x00, 0x69, 0x01, 0x95, 0x56, 0x90, 0xaa, 0x16, 0x55, 0x55, 0x41, 0x55, 0x15,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x96, 0x5a, 0x55, 0x6a,
+    0x45, 0xa9, 0x55, 0xa5, 0x56, 0x91, 0xaa, 0x5a, 0x55, 0x55, 0x45, 0x55, 0x55,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x55, 0x55, 0x5a, 0x54, 0x6a,
+    0x55, 0x55, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x00, 0x55, 0x00, 0x94, 0x16, 0x50, 0x6a, 0x41, 0xa9, 0x16, 0xa5, 0x69,
+    0x91, 0x96, 0x16, 0xa9, 0xaa, 0x55, 0x95, 0x56, 0x54, 0x55, 0x05, 0x40, 0x15,
+    0x0a, 0x55, 0x55, 0x95, 0xaa, 0x5a, 0x69, 0x55, 0x95, 0xaa, 0x56, 0x55, 0xa5,
+    0x55, 0x55, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x50, 0x15, 0x40, 0xa9, 0x05, 0xa5, 0x55, 0x90, 0x56, 0x05, 0xa9, 0x6a,
+    0x91, 0x56, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x55, 0x55, 0x91, 0xaa, 0x5a, 0x55, 0x69, 0x45, 0x95, 0x56, 0x40, 0x5a,
+    0x01, 0xa5, 0x15, 0x90, 0x56, 0x00, 0x69, 0x05, 0x50, 0x15, 0x00, 0x54, 0x01,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x5a, 0x5a, 0xa5, 0x6a,
+    0x95, 0x96, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0xa5, 0xaa,
+    0x45, 0x55, 0x5a, 0x50, 0x69, 0x05, 0xa9, 0x55, 0x50, 0x55, 0x01, 0x54, 0x05,
+    0x05, 0x00, 0x00, 0x50, 0x05, 0x00, 0x69, 0x01, 0x90, 0x16, 0x00, 0x55, 0x01,
+    0x90, 0x16, 0x00, 0x69, 0x01, 0x50, 0x15, 0x00, 0x54, 0x01, 0x00, 0x00, 0x00,
+    0x06, 0x00, 0x00, 0x40, 0x15, 0x00, 0xa4, 0x05, 0x40, 0x5a, 0x00, 0x54, 0x05,
+    0x40, 0x5a, 0x00, 0xa5, 0x05, 0x90, 0x56, 0x00, 0x55, 0x05, 0x40, 0x15, 0x00,
+    0x08, 0x40, 0x15, 0x00, 0xa5, 0x05, 0x94, 0x56, 0x50, 0x5a, 0x05, 0x69, 0x15,
+    0x50, 0x5a, 0x00, 0x94, 0x16, 0x00, 0xa5, 0x05, 0x40, 0x55, 0x00, 0x50, 0x05,
+    0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x55, 0x01, 0x90, 0x5a, 0x00, 0x55, 0x05,
+    0x90, 0x5a, 0x00, 0x55, 0x05, 0x40, 0x55, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x08, 0x55, 0x00, 0x90, 0x16, 0x00, 0xa5, 0x05, 0x40, 0x69, 0x01, 0x50, 0x5a,
+    0x40, 0x69, 0x05, 0xa5, 0x55, 0x90, 0x56, 0x01, 0x55, 0x05, 0x40, 0x15, 0x00,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x55, 0x55, 0x5a, 0x54, 0x6a,
+    0x05, 0x69, 0x55, 0x50, 0x55, 0x01, 0x69, 0x01, 0x50, 0x15, 0x00, 0x54, 0x01,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0xa9, 0x59, 0x99, 0x99,
+    0x95, 0xa9, 0x5a, 0x69, 0x55, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x01, 0x55, 0x15,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x69, 0xa5,
+    0x95, 0xaa, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x0a, 0x55, 0x55, 0x90, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0xa9, 0x6a,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0xaa, 0x56, 0x55, 0x55, 0x45, 0x55, 0x15,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x55, 0x69, 0x55,
+    0x95, 0x56, 0x15, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x55, 0x15, 0x90, 0xaa, 0x05, 0x69, 0x69, 0x91, 0x56, 0x5a, 0x69, 0xa5,
+    0x95, 0x56, 0x5a, 0x69, 0x69, 0x95, 0xaa, 0x55, 0x55, 0x55, 0x41, 0x55, 0x05,
+    0x0a, 0x55, 0x55, 0x91, 0xaa, 0x5a, 0x69, 0x55, 0x95, 0x56, 0x55, 0xa9, 0x6a,
+    0x91, 0x56, 0x15, 0x69, 0x55, 0x91, 0xaa, 0x5a, 0x55, 0x55, 0x45, 0x55, 0x55,
+    0x0a, 0x55, 0x55, 0x91, 0xaa, 0x5a, 0x69, 0x55, 0x95, 0x56, 0x55, 0xa9, 0x6a,
+    0x91, 0x56, 0x15, 0x69, 0x55, 0x91, 0x16, 0x00, 0x55, 0x01, 0x40, 0x15, 0x00,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x55, 0x69, 0xa9,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x59, 0x54, 0x55, 0x05, 0x55, 0x55,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0xa9, 0xaa,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x05, 0x55, 0x00, 0x90, 0x16, 0x00, 0x69, 0x01, 0x90, 0x16, 0x00, 0x69, 0x01,
+    0x90, 0x16, 0x00, 0x69, 0x01, 0x90, 0x16, 0x00, 0x55, 0x01, 0x40, 0x15, 0x00,
+    0x0a, 0x00, 0x54, 0x01, 0x40, 0x5a, 0x00, 0xa4, 0x05, 0x40, 0x5a, 0x55, 0xa5,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0x69, 0x69, 0x95, 0xa6, 0x55, 0xa9, 0x56,
+    0x91, 0xa6, 0x05, 0x69, 0x69, 0x91, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x09, 0x55, 0x00, 0x90, 0x16, 0x00, 0x69, 0x01, 0x90, 0x16, 0x00, 0x69, 0x01,
+    0x90, 0x16, 0x00, 0x69, 0x55, 0x90, 0xaa, 0x16, 0x55, 0x55, 0x41, 0x55, 0x15,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0xa9, 0xa9, 0x95, 0xaa, 0x5a, 0x69, 0xa6,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0xa9, 0xa5, 0x95, 0x6a, 0x5a, 0x69, 0xaa,
+    0x95, 0x96, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x69, 0xa5,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x55, 0x55, 0x90, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x69, 0xa5,
+    0x95, 0xaa, 0x56, 0x69, 0x55, 0x95, 0x56, 0x15, 0x55, 0x01, 0x40, 0x15, 0x00,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x69, 0xa5,
+    0x95, 0x56, 0x5a, 0x69, 0x69, 0x55, 0xaa, 0x5a, 0x54, 0x55, 0x05, 0x55, 0x55,
+    0x0a, 0x55, 0x55, 0x90, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0xa9, 0x6a,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x0a, 0x54, 0x55, 0x50, 0xaa, 0x16, 0x69, 0xa5, 0x95, 0x56, 0x55, 0xa5, 0x6a,
+    0x55, 0x55, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x09, 0x55, 0x55, 0x90, 0xaa, 0x16, 0x95, 0x56, 0x01, 0x69, 0x15, 0x90, 0x16,
+    0x00, 0x69, 0x01, 0x90, 0x16, 0x00, 0x69, 0x01, 0x50, 0x15, 0x00, 0x54, 0x01,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x69, 0xa5,
+    0x95, 0x56, 0x5a, 0x69, 0xa5, 0x55, 0xaa, 0x56, 0x54, 0x55, 0x05, 0x55, 0x15,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x69, 0xa5,
+    0x55, 0x9a, 0x56, 0x94, 0x5a, 0x05, 0x65, 0x15, 0x40, 0x55, 0x00, 0x50, 0x01,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0x69, 0xa5, 0x95, 0x56, 0x5a, 0x69, 0xa6,
+    0x95, 0xaa, 0x5a, 0xa9, 0xa9, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x0a, 0x55, 0x54, 0x91, 0x56, 0x5a, 0xa9, 0xa9, 0x55, 0xaa, 0x56, 0x94, 0x5a,
+    0x55, 0xaa, 0x16, 0xa9, 0xa9, 0x95, 0x56, 0x5a, 0x55, 0x55, 0x45, 0x15, 0x55,
+    0x09, 0x55, 0x55, 0x90, 0x96, 0x16, 0x69, 0x69, 0x91, 0x96, 0x16, 0xa5, 0x5a,
+    0x41, 0x69, 0x15, 0x90, 0x56, 0x00, 0x69, 0x01, 0x50, 0x15, 0x00, 0x54, 0x01,
+    0x0a, 0x55, 0x55, 0x91, 0xaa, 0x5a, 0x55, 0xa9, 0x05, 0xa5, 0x56, 0x94, 0x5a,
+    0x55, 0x6a, 0x15, 0xa9, 0x55, 0x91, 0xaa, 0x5a, 0x55, 0x55, 0x45, 0x55, 0x55,
+    0x06, 0x55, 0x01, 0x90, 0x5a, 0x00, 0x69, 0x05, 0x90, 0x56, 0x00, 0x69, 0x01,
+    0x90, 0x16, 0x00, 0x69, 0x01, 0x90, 0x5a, 0x00, 0x55, 0x05, 0x40, 0x55, 0x00,
+    0x07, 0x55, 0x00, 0x90, 0x16, 0x00, 0x69, 0x01, 0x50, 0x5a, 0x00, 0xa4, 0x05,
+    0x40, 0x5a, 0x00, 0x94, 0x16, 0x00, 0x69, 0x01, 0x50, 0x15, 0x00, 0x54, 0x01,
+    0x06, 0x55, 0x01, 0x90, 0x5a, 0x00, 0xa5, 0x05, 0x40, 0x5a, 0x00, 0xa4, 0x05,
+    0x40, 0x5a, 0x00, 0xa5, 0x05, 0x90, 0x5a, 0x00, 0x55, 0x05, 0x40, 0x55, 0x00,
+    0x08, 0x50, 0x01, 0x40, 0x59, 0x00, 0xa5, 0x16, 0x90, 0xa6, 0x05, 0x59, 0x59,
+    0x50, 0x55, 0x05, 0x54, 0x54, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x0a, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x55, 0x55, 0x91, 0xaa, 0x5a, 0x55, 0x55, 0x45, 0x55, 0x55,
+    0x07, 0x55, 0x00, 0x90, 0x16, 0x00, 0xa5, 0x05, 0x40, 0x69, 0x01, 0x50, 0x15,
+    0x00, 0x54, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x07, 0x50, 0x05, 0x40, 0x69, 0x01, 0xa4, 0x15, 0x50, 0x5a, 0x01, 0x69, 0x05,
+    0x50, 0x5a, 0x00, 0xa4, 0x05, 0x40, 0x69, 0x01, 0x50, 0x15, 0x00, 0x54, 0x01,
+    0x04, 0x15, 0x00, 0x90, 0x05, 0x00, 0x59, 0x00, 0x90, 0x05, 0x00, 0x59, 0x00,
+    0x90, 0x05, 0x00, 0x59, 0x00, 0x90, 0x05, 0x00, 0x55, 0x00, 0x40, 0x05, 0x00,
+    0x07, 0x55, 0x00, 0x90, 0x16, 0x00, 0xa5, 0x05, 0x40, 0x5a, 0x00, 0x94, 0x16,
+    0x40, 0x5a, 0x01, 0xa5, 0x15, 0x90, 0x56, 0x00, 0x55, 0x05, 0x40, 0x15, 0x00,
+    0x0a, 0x00, 0x00, 0x00, 0x00, 0x00, 0x54, 0x55, 0x51, 0x6a, 0x5a, 0x69, 0x6a,
+    0x55, 0x55, 0x55, 0x54, 0x55, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+};

src/overlay.c

@@ -0,0 +1,62 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "overlay.h"
+
+
+int overlay_init(Overlay* overlay) {
+    overlay->messages = NULL;
+    overlay->next_id = 0;
+    return 0;
+}
+
+int overlay_clear(Overlay* overlay) {
+    int n_cleared = 0;
+    for (   overlay_message* message = overlay->messages;
+            NULL != message;
+            message = message->next) {
+        free(message->string);
+        free(message);
+        ++n_cleared;
+    }
+    overlay_init(overlay);
+    return n_cleared;
+}
+
+int overlay_clear_message(Overlay* overlay, int id) {
+    int result = -1;
+    overlay_message* last = NULL;
+    overlay_message* message = overlay->messages;
+    for (   ;
+            NULL != message && message->id != id;
+            last = message, message = message->next
+        );
+    if (NULL != message) {
+        result = 0;
+        if (NULL == last) {
+            overlay->messages = message->next;
+        } else {
+            last->next = message->next;
+        }
+        free(message->string);
+        free(message);
+    }
+    return result;
+}
+
+int overlay_add_message(Overlay* overlay,
+                        const char* string, int expiry) {
+    overlay_message* message = calloc(1, sizeof(*message));
+    message->string = strdup(string);
+    message->id     = ++(overlay->next_id);
+    message->expiry = expiry;
+    message->next   = NULL;
+    if (NULL == overlay->messages) {
+        overlay->messages = message;
+    } else {
+        overlay_message* last = overlay->messages;
+        for ( ; NULL != last->next; last = last->next);
+        last->next = message;
+    }
+    return message->id;
+}

src/overlay.h

@@ -0,0 +1,25 @@
+#ifndef NESE_OVERLAY_H_
+#define NESE_OVERLAY_H_
+
+
+typedef struct overlay_message_t {
+    char* string;
+    int id;
+    int expiry;
+    struct overlay_message_t* next;
+} overlay_message;
+
+
+typedef struct {
+    overlay_message* messages;
+    int next_id;
+} Overlay;
+
+
+int overlay_init(Overlay*);
+int overlay_add_message(Overlay*, const char*, int expiry);
+int overlay_clear_message(Overlay*, int id);
+int overlay_clear(Overlay*);
+
+
+#endif // NESE_OVERLAY_H_

src/render.h

@@ -2,12 +2,14 @@
 #define NES_RENDER_H_
 
 #include "ppu.h"
+#include "overlay.h"
 
 
 typedef struct nes_Renderer_t {
     int (*init)(struct nes_Renderer_t*);
     void (*done)(struct nes_Renderer_t*);
     int (*render)(struct nes_Renderer_t*, nes_ppu*);
+    Overlay overlay;
     void* data;
 } nes_Renderer;
 

src/sdl_overlay.c

@@ -0,0 +1,135 @@
+#include "sdl_overlay.h"
+
+#include "charbits.h"
+
+
+typedef struct {
+    const uint8_t* bits;
+    uint8_t shift;
+} bit_buffer;
+
+void make_bit_buffer(bit_buffer* buf, const uint8_t* bits) {
+    buf->bits = bits;
+    buf->shift = 0;
+}
+
+uint8_t get_bits(bit_buffer* buf) {
+    uint8_t val = ((buf->bits[0] >> buf->shift) & 3);
+    if (buf->shift == 6) {
+        buf->shift = 0;
+        buf->bits++;
+    } else {
+        buf->shift += 2;
+    }
+    return val;
+}
+
+static const SDL_Color pal[2] = {
+    {0, 0, 0}, {255, 255, 255}
+};
+
+static SDL_Surface* create_char_surface(const uint8_t* bits) {
+    int w = *bits++;
+    bit_buffer buf = {0};
+    make_bit_buffer(&buf, bits);
+
+    SDL_Surface* surface = SDL_CreateRGBSurfaceWithFormat(
+            0, w, char_h, 8, SDL_PIXELFORMAT_INDEX8
+        );
+    SDL_SetPaletteColors(surface->format->palette, pal, 1U, 2U);
+    SDL_SetColorKey(surface, SDL_TRUE, 0);
+
+    uint8_t* line = surface->pixels;
+    for (int y = char_h; y > 0; --y) {
+        uint8_t* dst = line;
+        for (int x = w; x > 0; --x) {
+            *dst++ = get_bits(&buf);
+        }
+        for (int x = (char_w - w); x > 0; --x) get_bits(&buf);
+        line += surface->pitch;
+    }
+
+    return surface;
+}
+
+int sdl_overlay_font_init(sdl_overlay_font* font) {
+    font->chars = chars;
+    font->charbits = charbits;
+    font->char_count = char_count;
+    font->surfaces = calloc(char_count, sizeof(SDL_Surface*));
+    for (int i = 0; i < font->char_count; ++i) {
+        font->surfaces[i] = create_char_surface(
+                &font->charbits[i * charbit_size]
+            );
+    }
+    return 0;
+}
+
+void sdl_overlay_font_done(sdl_overlay_font* font) {
+    for (int i = 0; i < font->char_count; ++i) {
+        SDL_FreeSurface(font->surfaces[i]);
+    }
+}
+
+#define overlay_start_x (char_w / 2)
+#define overlay_start_y (char_h / 2)
+
+static inline int char_index(char c) {
+    if (c >= 'a' && c <= 'z') c += ('A' - 'a');
+    if (c > ' ' && c < 'a') return (c - ' ');
+    if (c >= '{' && c <= '~') return (65 + c - '{');
+    return 0;
+}
+
+static void render_string(SDL_Surface* target,
+                          int x, int y,
+                          sdl_overlay_font* font,
+                          const char* string) {
+    SDL_Rect rect = {
+        .x = x,
+        .y = y,
+        .w = char_w,
+        .h = char_h,
+    };
+
+    for (const char* c = string; *c; ++c) {
+        if (*c == ' ') {
+            rect.x += (char_w / 2) - 1;
+        } else {
+            SDL_Surface* surface = font->surfaces[
+                    char_index(*c)
+                ];
+
+            SDL_BlitSurface(surface, NULL, target, &rect);
+
+            rect.x += (surface->w - 1);
+        }
+    }
+}
+
+int sdl_overlay_frame(Overlay* overlay, sdl_overlay_font* font,
+                      SDL_Surface* target) {
+    int y = overlay_start_y;
+    overlay_message* last = NULL, *next = NULL;
+    for (   overlay_message* message = overlay->messages;
+            NULL != message;
+            last = message, message = next) {
+        next = message->next;
+
+        render_string(target, overlay_start_x, y,
+                      font, message->string);
+        y += (char_h + 1);
+
+        if (message->expiry > 0 && --(message->expiry) == 0) {
+            if (NULL == last) {
+                overlay->messages = message->next;
+            } else {
+                last->next = message->next;
+            }
+            free(message->string);
+            free(message);
+        }
+    }
+
+    return 0;
+}

src/sdl_overlay.h

@@ -0,0 +1,26 @@
+#ifndef NESE_SDL_OVERLAY_
+#define NESE_SDL_OVERLAY_
+
+#include <stdint.h>
+
+#include <SDL2/SDL.h>
+
+#include "overlay.h"
+
+
+typedef struct {
+    const char* chars;
+    const uint8_t* charbits;
+    int char_count;
+    SDL_Surface** surfaces;
+} sdl_overlay_font;
+
+
+int sdl_overlay_font_init(sdl_overlay_font*);
+
+void sdl_overlay_font_done(sdl_overlay_font*);
+
+int sdl_overlay_frame(Overlay*, sdl_overlay_font*, SDL_Surface*);
+
+
+#endif // NESE_SDL_OVERLAY_

src/sdl_render.c

@@ -5,6 +5,7 @@
 #include "render.h"
 #include "ppu.h"
 #include "mapper.h"
+#include "sdl_overlay.h"
 
 
 static SDL_Color nes_palette[64] = {
@@ -44,6 +45,7 @@ typedef struct {
     SDL_Surface* foreground;
     SDL_Surface* sprite;
     SDL_Surface* target;
+    sdl_overlay_font font;
 } sdl_render_data;
 
 static sdl_render_data the_render_data = {0};
@@ -51,6 +53,11 @@ static sdl_render_data the_render_data = {0};
 
 static int sdl_render_init(nes_Renderer* rend) {
     sdl_render_data* data = &the_render_data;
+
+    overlay_init(&rend->overlay);
+    // TODO: Cleanup
+    sdl_overlay_font_init(&data->font);
+
     int status = SDL_Init(SDL_INIT_VIDEO);
 
     if (0 != status) {
@@ -566,6 +573,9 @@ static int sdl_render(nes_Renderer* rend, nes_ppu* ppu) {
     } else {
         REND_LOG("Scanline %3d -> Postrender\n", ppu->scanline);
 
+        sdl_overlay_frame(&rend->overlay, &data->font,
+                          data->target);
+
         SDL_Texture* texture = SDL_CreateTextureFromSurface(
                 data->renderer, data->target
             );