1 files changed, 142 insertions, 0 deletions

diff --git a/src/text.h b/src/text.h
new file mode 100644
index 0000000..e38c220
--- /dev/null
+++ b/src/text.h
@@ -0,0 +1,142 @@
+#ifndef GBAEXP_TILES_H
+#define GBAEXP_TILES_H
+
+#include <stdarg.h>
+
+#include "common.h"
+#include "bd-font.c"
+
+typedef struct TextEngine {
+    // Currently working on tiled backgrounds only. The X and Y positions
+    // correspond to the tile X and Y starting from the top left of the screen.
+    // For a 240x160 screen, we have 30x20 tiles available.
+    size_t cursor_x;
+    size_t cursor_y;
+    // Pointer to the screenblock being used for writing to the screen.
+    u16 *screenblock;
+} TextEngine;
+
+static TextEngine text_engine = {0};
+
+void
+txt_putc(char c) {
+    if (c == '\0') {
+        return;
+    }
+    if (c == '\n') {
+        text_engine.cursor_x = 0;
+        text_engine.cursor_y++;
+    } else {
+        text_engine.screenblock[text_engine.cursor_x + 32 * text_engine.cursor_y] = c;
+        text_engine.cursor_x++;
+        if (text_engine.cursor_x >= 30) {
+            text_engine.cursor_x = 0;
+            text_engine.cursor_y++;
+        }
+    }
+    if (text_engine.cursor_y >= 20) {
+        text_engine.cursor_y = 0;
+    }
+}
+
+static inline void
+txt_puts(char *msg) {
+    while (*msg) {
+        txt_putc(*msg++);
+    }
+}
+
+void
+txt_init(size_t bg, Color clr, size_t cb_idx) {
+    // The screenblock for the tile map should start after the tile memory
+    // (MEM_VRAM + 0x2000 for 256 characters). Since each screenblock is
+    // composed of 1024 screenblock entries of u16 (2 bytes), we need an
+    // screenblock index offset of 8192 / (1024 * 2) = 4 screen blocks.
+    size_t sb_idx = cb_idx * 8 + 4;
+
+    // Set the background parameters for the text layer.
+    BG_CTRL(bg) = BG_CHARBLOCK(cb_idx) | BG_SCREENBLOCK(sb_idx) | BG_PRIORITY(3);
+
+    // Load font data in video memory. Each character is unpacked into a tile of
+    // 8 32bit values (4bpp), meaning that for the full ASCII set of 256
+    // characters, we need 8192 bytes of VRAM (8 * 4 * 256).
+    unpack_tiles(&bd_font, &CHARBLOCK_MEM[cb_idx], 256);
+
+    // Load palette color.
+    PAL_BUFFER_BG[1] = clr;
+
+    // Update text_engine variables.
+    text_engine.screenblock = SCREENBLOCK_MEM[sb_idx];
+}
+
+// Print text to the screen with formatting.
+void
+txt_printf(char *msg, ...) {
+    va_list arg_list;
+    va_start(arg_list, msg);
+    char c;
+    char prev_c;
+    while ((c = *msg++) != '\0') {
+        if (c != '%') {
+            txt_putc(c);
+            prev_c = c;
+            continue;
+        }
+        c = *msg++;
+        switch (c) {
+            case 's': {
+                txt_puts(va_arg(arg_list, char *));
+            } break;
+            case 'd': {
+                char buf[32] = {0};
+                int x = va_arg(arg_list, int);
+                sprintf(buf, "%d", x);
+                txt_puts(buf);
+            } break;
+            case 'u': {
+                char buf[32] = {0};
+                unsigned int x = va_arg(arg_list, unsigned int);
+                sprintf(buf, "%u", x);
+                txt_puts(buf);
+            } break;
+            case 'x': {
+                char buf[32] = {0};
+                unsigned int x = va_arg(arg_list, unsigned int);
+                sprintf(buf, "%x", x);
+                txt_puts(buf);
+            } break;
+            default: {
+                txt_putc('%');
+                txt_putc(c);
+            } break;
+        }
+    }
+}
+
+void
+txt_clear_line(void) {
+    for (size_t i = 0; i < 30; ++i) {
+        text_engine.screenblock[i + 32 * text_engine.cursor_y] = ' ';
+    }
+    text_engine.cursor_x = 0;
+}
+
+void
+txt_clear_screen(void) {
+    for (size_t j = 0; j < 20; ++j) {
+        for (size_t i = 0; i < 30; ++i) {
+            text_engine.screenblock[i + 32 * j] = ' ';
+        }
+    }
+    text_engine.cursor_x = 0;
+    text_engine.cursor_y = 0;
+}
+
+void
+txt_position(size_t tile_x, size_t tile_y) {
+    text_engine.cursor_x = tile_x;
+    text_engine.cursor_y = tile_y;
+}
+
+#endif // GBAEXP_TILES_H
+