void vga_move_cursor(uint8_t column, uint8_t row) {
cursor_row = row;
cursor_column = column;
/* wrap if the right-most edge of the screen is reached */
if (cursor_column > VGA_WIDTH - 1) {
cursor_row++;
cursor_column = 0;
}
/* scroll the screen if the cursor has fallen off the bottom XXX make this use memcpy once memcpy works */
if (cursor_row > VGA_HEIGHT - 1) {
cursor_row = VGA_HEIGHT - 1;
/* scroll up VGA memory by one line */
memcpy(VGA_MEMORY, VGA_MEMORY + VGA_WIDTH, (VGA_HEIGHT * VGA_WIDTH - VGA_WIDTH) * 2);
/* blank the freshly exposed bottom line */
for (size_t index = 0; index < VGA_WIDTH; index++) {
VGA_MEMORY[(VGA_HEIGHT - 1) * VGA_WIDTH + index] = vga_character(' ');
}
}
/* poke the VGA ports to move the cursor XXX strictly the base port should be queried from the BIOS not hardcoded */
outb(0x3D4, 0x0F);
outb(0x3D5, (unsigned char)(vga_cursor_memory_index() & 0xFF));
outb(0x3D4, 0x0E);
outb(0x3D5, (unsigned char )((vga_cursor_memory_index() >> 8) & 0xFF));
}
/* clear the terminal and move the cursor back to the top left */
void terminal_clear() {
for (uint8_t row = 0; row < VGA_HEIGHT; row++) {
for (uint8_t column = 0; column < VGA_WIDTH; column++) {
VGA_MEMORY[row * VGA_WIDTH + column] = vga_character(' ');
}
}
vga_move_cursor(0, 0);
}
void vga_initialize() {
vga_row = 0;
vga_column = 0;
vga_color_palette = vga_color_palette_byte(kColorLightGray, kColorBlack);
vga_buffer = (VgaCharacter *) kVgaBuffer;
for (size_t entry = 0; entry < kVgaWidth * kVgaHeight; entry++) {
vga_buffer[entry] = vga_character(' ', vga_color_palette);
}
}
/* write a null terminated string at the current cursor position. handles \n for newlines. */
void terminal_write(char *string) {
for (size_t index = 0; string[index] != 0; index++) {
if (string[index] == '\n') {
vga_move_cursor(0, ++cursor_row);
} else {
VGA_MEMORY[vga_cursor_memory_index()] = vga_character(string[index]);
vga_move_cursor(++cursor_column, cursor_row);
}
}
}
void vga_place_character(char character, uint8_t color_palette, int row, int column) {
const int index = row * kVgaWidth + column;
vga_buffer[index] = vga_character(character, color_palette);
}
