1 files changed, 61 insertions, 0 deletions
diff --git a/src/vga.cc b/src/vga.cc
new file mode 100644
index 0000000..83d0060
--- /dev/null
+++ b/src/vga.cc
@@ -0,0 +1,61 @@
+#include "vga.h"
+#include <string.h>
+
+constexpr uint8_t vga_entry_color(VGA::vga_color fg, VGA::vga_color bg) {
+  return fg | bg << 4;
+}
+
+constexpr uint16_t vga_entry(unsigned char uc, uint8_t color) {
+  return (uint16_t)uc | (uint16_t)color << 8;
+}
+
+VGA::VGA(vga_color fg, vga_color bg, uint32_t address) {
+  color = vga_entry_color(fg, bg);
+  buffer = (uint16_t*)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] = vga_entry(' ', color);
+    }
+  }
+}
+
+void VGA::write(char c) {
+  switch (c) {
+    case '\n':
+      column = 0;
+      ++row;
+      break;
+    default: {
+      const size_t index = row * max_columns + column;
+      buffer[index] = vga_entry(c, (color == 0) ? this->color : color);
+      ++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];
+      }
+    }
+    --row;
+  }
+}
+
+void VGA::write(ViewIterator& iter) {
+  while (iter) {
+    write(iter.next());
+  }
+}