[Teton] Load a font file and write a character to the screen.

sys/teton/framebuffer/psf.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <mammoth/memory_region.h>
+
+struct PsfHeader {
+  uint32_t magic;         /* magic bytes to identify PSF */
+  uint32_t version;       /* zero */
+  uint32_t headersize;    /* offset of bitmaps in file, 32 */
+  uint32_t flags;         /* 0 if there's no unicode table */
+  uint32_t numglyph;      /* number of glyphs */
+  uint32_t bytesperglyph; /* size of each glyph */
+  uint32_t height;        /* height in pixels */
+  uint32_t width;         /* width in pixels */
+};
+
+class Psf {
+ public:
+  Psf(OwnedMemoryRegion&& psf_file);
+
+  void DumpHeader();
+
+  uint32_t size() { return header_->numglyph; }
+
+  uint8_t* glyph(uint32_t index) {
+    return reinterpret_cast<uint8_t*>(psf_file_.vaddr() + header_->headersize +
+                                      (index * header_->bytesperglyph));
+  }
+
+ private:
+  OwnedMemoryRegion psf_file_;
+  PsfHeader* header_;
+
+  void EnsureValid();
+};