camera: implement fixed cursor movement

On platforms with PERIPHERAL_TYPE_PAD, navigating through menus and
options can be cumbersome if moving the cursor freely around the
screen.

Therefore, this commit instead defines a list of (X, Y) coordinates that
the cursor can jump to. The implementation also attempts to guess which
direction the cursor should jump to for the previous/next point, and
hence determine which button should be pressed by the user.

src/camera/inc/camera.h

@@ -35,6 +35,16 @@ struct camera
         {
             int last_w, last_h;
         } screen;
+
+        struct cursor_pos_rt
+        {
+            const struct cursor_pos
+            {
+                unsigned x, y;
+            } *list;
+
+            size_t i, n;
+        } rt;
     } cursor;
 };
 
@@ -45,6 +55,7 @@ bool camera_translate(const struct camera *cam, const struct util_rect *dim, sho
 void cursor_init(struct cursor *c);
 bool cursor_collision(const struct camera *cam, const struct util_rect *d);
 void cursor_pos(const struct camera *cam, unsigned long *x, unsigned long *y);
+void cursor_set_pos_list(struct cursor *c, const struct cursor_pos *pos, size_t n);
 int cursor_render(const struct cursor *c);
 
 #ifdef __cplusplus

src/camera/src/camera.c

@@ -114,6 +114,16 @@ bool camera_translate(const struct camera *const cam, const struct util_rect *co
     return true;
 }
 
+void cursor_set_pos_list(struct cursor *const c,
+    const struct cursor_pos *const pos, const size_t n)
+{
+    c->rt = (const struct cursor_pos_rt)
+    {
+        .list = pos,
+        .n = n
+    };
+}
+
 void camera_update(struct camera *const cam, const union peripheral *const p)
 {
     switch (p->common.type)

src/camera/src/pad.c

@@ -5,6 +5,7 @@
 #include <gfx.h>
 #include <util.h>
 #include <stdbool.h>
+#include <stdlib.h>
 
 static void cursor_update(struct camera *const cam, const struct pad *const p)
 {
@@ -99,9 +100,61 @@ static void update_speed(struct camera *const cam, const struct pad *const p)
         cam->y_speed = 0;
 }
 
+static enum pad_key get_ref_key(struct cursor_pos_rt *const rt,
+    const size_t ref)
+{
+    enum pad_key key;
+
+    const struct cursor_pos *const cur = &rt->list[rt->i],
+        *const next = &rt->list[ref];
+    const short nx = next->x - cur->x,
+        ny = next->y - cur->y;
+
+    if (abs(nx) > abs(ny))
+        key = nx > 0 ? PAD_KEY_RIGHT : PAD_KEY_LEFT;
+    else
+        key = ny > 0 ? PAD_KEY_DOWN : PAD_KEY_UP;
+
+    return key;
+}
+
+static void cursor_update_fixed(struct camera *const cam,
+    const struct pad *const p)
+{
+    struct cursor *const c = &cam->cursor;
+    struct cursor_pos_rt *const rt = &c->rt;
+    const size_t next = rt->i + 1;
+
+    if (next < rt->n)
+    {
+        const enum pad_key key = get_ref_key(rt, next);
+
+        if (pad_justpressed(p, key))
+            rt->i = next;
+    }
+    else if (rt->i)
+    {
+        const size_t prev = rt->i - 1;
+        const enum pad_key key = get_ref_key(rt, prev);
+
+        if (pad_justpressed(p, key))
+            rt->i = prev;
+    }
+
+    const struct cursor_pos *const cur = &rt->list[rt->i];
+
+    c->x = cur->x;
+    c->y = cur->y;
+}
+
 void camera_update_pad(struct camera *const cam, const struct pad *const p)
 {
-    cursor_update(cam, p);
-    update_speed(cam, p);
-    camera_update_pos(cam);
+    if (cam->cursor.rt.list)
+        cursor_update_fixed(cam, p);
+    else
+    {
+        cursor_update(cam, p);
+        update_speed(cam, p);
+        camera_update_pos(cam);
+    }
 }