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#include "cga.h"
#include <string.h>
static_assert(sizeof(CGA::Entry) == 2);
/* cga registers, see https://www.lowlevel.eu/wiki/Color_Graphics_Adapter */
constexpr uint8_t cursor_start = 10; // 0xa
constexpr uint8_t cursor_end = 11; // 0xb
constexpr uint8_t cursor_addr_h = 14; // 0xe
constexpr uint8_t cursor_addr_l = 15; // 0xf
/* cursor format
* register | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
* start | | e | t | scanline |
* end | | scanline |
* e = enable; t = timing
* e t | effect
* 0 0 | no blinking
* 0 1 | hide cursor
* 1 0 | blink normally
* 1 1 | blink fast
*/
constexpr uint8_t cursor_hide = 0b00100000;
CGA::CGA(Colour fg, Colour bg, uint32_t address) : colour_fg(fg), colour_bg(bg) {
buffer = reinterpret_cast<Entry*>(address);
// clear buffer
for (size_t y = 0; y < max_rows; y++) {
for (size_t x = 0; x < max_columns; x++) {
const size_t index = y * max_columns + x;
buffer[index].c = ' ';
buffer[index].fg = colour_fg;
buffer[index].bg = colour_bg;
}
}
enable_cursor(14, 15);
update_cursor();
}
void CGA::set_colour(Colour fg, Colour bg) {
colour_fg = fg;
colour_bg = bg;
for (size_t y = 0; y < max_rows; y++) {
for (size_t x = 0; x < max_columns; x++) {
const size_t index = y * max_columns + x;
buffer[index].fg = colour_fg;
buffer[index].bg = colour_bg;
}
}
}
void CGA::enable_cursor(uint8_t start, uint8_t end) {
p_idx.write(cursor_start);
p_dat.write((p_dat.read() & 0xc0) | start);
p_idx.write(cursor_end);
p_dat.write((p_dat.read() & 0xe0) | end);
}
void CGA::disable_cursor() {
p_idx.write(cursor_start);
p_dat.write(cursor_hide);
}
void CGA::update_cursor() {
const uint16_t pos = row * max_columns + column;
p_idx.write(cursor_addr_l);
p_dat.write(static_cast<uint8_t>(pos & 0xff));
p_idx.write(cursor_addr_h);
p_dat.write(static_cast<uint8_t>((pos >> 8) & 0xff));
}
void CGA::write(char c) {
switch (c) {
case '\n':
column = 0;
++row;
break;
default: {
const size_t index = row * max_columns + column;
buffer[index].c = c;
++column;
}
}
if (column == max_columns) {
column = 0;
++row;
}
if (row == max_rows) {
// scroll up - move rows 1~25 up by one
for (size_t y = 1; y < max_rows; y++) {
const auto prev_y = y - 1;
for (size_t x = 0; x < max_columns; ++x) {
const auto prev = prev_y * max_columns + x;
const auto idx = y * max_columns + x;
buffer[prev] = buffer[idx];
}
}
// blank out last row
for (size_t idx = (max_rows - 1) * max_columns; idx < max_rows * max_columns; ++idx) {
buffer[idx].c = ' ';
}
--row;
}
}
void CGA::write(ViewIterator& iter) {
while (iter) {
write(iter.next());
}
}
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