Add initial text background drawing functions

1 files changed, 114 insertions, 0 deletions

diff --git a/src/text/text.h b/src/text/text.h
new file mode 100644
index 0000000..65003c5
--- /dev/null
+++ b/src/text/text.h
@@ -0,0 +1,114 @@
+#ifndef TEXT_H
+#define TEXT_H
+
+#include "bd-font.c"
+#include "shorthand.h"
+#include "posprintf.h"
+
+typedef struct TextEngine {
+    // Cursor for tiled text mode 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;
+
+    // Memory location of font tile data and tilemap. Likely located on the
+    // VRAM.
+    u32 *font_data;
+    u16 *font_tilemap;
+
+    // The font map for tiled text. Writing the character stored in this
+    // position on the tilemap will show a character on the screen.
+    u16 font_map[256];
+} TextEngine;
+
+static TextEngine text_engine = {0};
+
+static inline
+void
+txt_init(u32 *font_data, u16 *font_tilemap, u16 font_offset) {
+    // Load font data into VRAM.
+    unpack_tiles(&bd_font, font_data, 256);
+
+    // Initialize the font map translation table. That way we can write
+    // a character on the text background layer with:
+    //     FONT_TILEMAP[tile_x + 32 * tile_y] = font_map['A'];
+    for (size_t i = 0; i < 256; ++i) {
+        text_engine.font_map[i] = font_offset + i;
+    }
+
+    // Initialize remaining variables.
+    text_engine.font_data = font_data;
+    text_engine.font_tilemap = font_tilemap;
+}
+
+static inline
+void
+txt_putc(char c) {
+    if (c == '\0') {
+        return;
+    }
+    if (c == '\n') {
+        text_engine.cursor_x = 0;
+        text_engine.cursor_y++;
+    } else {
+        int x = text_engine.cursor_x;
+        int y = text_engine.cursor_y;
+        text_engine.font_tilemap[x + 32 * y] = text_engine.font_map[(u16)c];
+        text_engine.cursor_x += 1;
+        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++);
+    }
+}
+
+static inline
+void
+txt_clear_line(void) {
+    for (size_t i = 0; i < 30; ++i) {
+        int x = text_engine.cursor_x;
+        int y = text_engine.cursor_y;
+        text_engine.font_tilemap[x + 32 * y] = text_engine.font_map[0];
+    }
+    text_engine.cursor_x = 0;
+}
+
+static inline
+void
+txt_clear_screen(void) {
+    for (size_t j = 0; j < 20; ++j) {
+        text_engine.cursor_y = j;
+        txt_clear_line();
+    }
+    text_engine.cursor_x = 0;
+    text_engine.cursor_y = 0;
+}
+
+static inline
+void
+txt_position(size_t tile_x, size_t tile_y) {
+    text_engine.cursor_x = tile_x;
+    text_engine.cursor_y = tile_y;
+}
+
+// Print text to the screen with formatting.
+#define txt_printf(msg, ...) \
+        { \
+                char buf[256] = {0}; \
+                posprintf(buf, msg, ##__VA_ARGS__); \
+                txt_puts(buf); \
+        }
+
+#endif // TEXT_H