diff --git a/src/_ct_shared.h b/src/_ct_shared.h
new file mode 100644
index 0000000..6e9cac6
--- /dev/null
+++ b/src/_ct_shared.h
@@ -0,0 +1,7 @@
+#ifndef _CURSETREE__SHARED_H
+#define _CURSETREE__SHARED_H
+
+#define OK (0)
+#define ERR (1)
+
+#endif /* _CURSETREE__SHARED_H */
diff --git a/src/surface.c b/src/surface.c
new file mode 100644
index 0000000..6c1fdbc
--- /dev/null
+++ b/src/surface.c
@@ -0,0 +1,163 @@
+#include <errno.h>
+#include <stdlib.h>
+
+#include "_ct_shared.h"
+#include "surface.h"
+
+#define ALLOC_ROW(w) ((char *)calloc(w, sizeof(char)))
+
+/* Allocates a new 2D surface buffer with ROWS=h, COLS=w.
+ * Returns NULL on failure and sets errno, otherwise
+ * a pointer to the new buffer is returned.
+ */
+static inline __attribute__((malloc, warn_unused_result)) char **
+sfbuf(const pos w, const pos h) {
+  char **buf;
+  pos i;
+
+  buf = (char **)malloc(sizeof(char *) * h);
+  if (buf == NULL)
+    return buf;
+
+  for (i = 0; i < w; i++) {
+    buf[i] = ALLOC_ROW(w);
+    if (buf[i] == NULL)
+      goto fail;
+  }
+  return buf;
+
+fail:
+  // Immediately decrement since we know the
+  // current index is where ALLOW_ROW() failed.
+  while (--i >= 0)
+    free(buf[i]);
+  free(buf);
+  return NULL;
+}
+
+/* Resize the width (columns) of a surface.
+ * Returns 0 on success, or a non-zero errno on failure.
+ * WARNING: Don't use sfseth directly, see sfresize()
+ * WARNING: and how it optimises based on how height changes.
+ */
+static inline int sfsetw(const pos w1, surface *const s) {
+  void *ptr;
+  pos i, w0 = s->w;
+  char **row;
+
+  errno = 0; // sanity check
+
+  if (w1 == w0)
+    return OK;
+  else if (w1 == 0) {
+    return EINVAL;
+  }
+
+  for (i = 0, row = s->buf; i < s->h; i++, row++) {
+    ptr = (void *)reallocarray(*row, w1, sizeof(char));
+    if (ptr == NULL) {
+      return errno;
+    }
+    *row = (char *)ptr;
+  }
+
+  s->w = w1;
+  return OK;
+}
+
+/* Resize the height (rows) of a surface.
+ * Returns 0 on success, or a non-zero errno on failure.
+ * WARNING: Don't use sfseth directly, see sfresize()
+ * WARNING: and how it optimises based on how height changes.
+ */
+static inline int sfseth(const pos h1, surface *const s) {
+  void *ptr;
+  pos i, h0 = s->h;
+  char **row;
+
+  errno = 0; // sanity check
+
+  if (h1 == h0)
+    return OK;
+  else if (h1 == 0) {
+    return EINVAL;
+  }
+
+  // height decreased (free bottom rows)
+  if (h1 < h0) {
+    for (i = h1, row = s->buf; i < h0; i++, row++) {
+      free(*row);
+    }
+  }
+
+  // use ptr to avoid losing unfreed s->buf
+  ptr = (void *)reallocarray(s->buf, h1, sizeof(char));
+  if (ptr == NULL)
+    return errno;
+  // ENOMEM X_X
+
+  s->buf = (char **)ptr;
+  s->h = h1;
+
+  // height increased (alloc bottom rows)
+  if (h1 > h0) {
+    for (i = h0, row = s->buf; i < h1; i++, row++) {
+      *row = ALLOC_ROW(s->w);
+      if (*row == NULL)
+        return errno;
+    }
+  }
+
+  s->h = h1;
+  return OK;
+}
+
+/*
+ */
+int sfresize(const pos w1, const pos h1, surface *const s) {
+  int retv;
+
+  /* Height is the 2D array's primary index dimension,
+   * whether it grows/shrinks determines whether it is
+   * optimal to resize width then height, or height then width.
+   * ie Height increasing but doing sfseth() before sfsetw()
+   * would result in new rows being allocated with the old width,
+   * then resized again to the new width (not optimal).
+   */
+  if (h1 > s->h) {
+    if ((retv = sfsetw(w1, s)) || (retv = sfseth(h1, s)))
+      return retv;
+  } else if ((retv = sfseth(h1, s)) || (retv = sfsetw(w1, s)))
+    return retv;
+  return OK;
+}
+
+__attribute__((malloc, warn_unused_result)) surface *sfalloc(const pos x, const pos y, const pos w, const pos h) {
+  surface *s;
+
+  char **buf = sfbuf(w, h);
+  if (buf == NULL)
+    return NULL;
+
+  s = (surface *)malloc(sizeof(struct ct_surface));
+  *s = (surface){
+      .x = x,
+      .y = y,
+      .w = w,
+      .h = y,
+      .vcx = 1,
+      .vcy = 1,
+      .buf = buf,
+  };
+
+  return s;
+}
+
+void sffree(surface *const s) {
+  pos i;
+  char **row;
+  for (i=0, row=s->buf; i < s->h; i++, row++) {
+    free(*row);
+  }
+  free(s->buf);
+}
diff --git a/src/surface.h b/src/surface.h
new file mode 100644
index 0000000..4744f30
--- /dev/null
+++ b/src/surface.h
@@ -0,0 +1,16 @@
+#ifndef _CURSETREE_SURFACE_H
+#define _CURSETREE_SURFACE_H
+
+/* Initial row and column coordinates */
+#define ROW0 1
+#define COL0 1
+
+typedef unsigned short pos;
+
+typedef struct ct_surface {
+  pos x, y, w, h;
+  char **buf;
+  pos vcx, vcy; /* virtual cursor position */
+} surface;
+
+#endif /* _CURSETREE_SURFACE_H */