stage: introduce stage_node_[sg]et_position()

Leaving the existing node aabb semantics as both sizing and placing the
node relative to the stage size and its center, add a simple means of
statefully shifting the aabb.

When the position is left unset, it's 0,0, and effectively a noop leaving
the aabb to exclusively size and place the node.  If you treat the aabb
as purely sizing the node, treating it as centered at 0,0 then you can
exclusively use this position api for placement of the node.

1 files changed, 22 insertions, 5 deletions

diff --git a/src/stage.c b/src/stage.c
index 20a1fc0..b50bc22 100644
--- a/src/stage.c
+++ b/src/stage.c
@@ -37,6 +37,7 @@ struct stage_node_t {
 	char			name[STAGE_NODE_NAME_MAX];
 	stage_cached_t		cached;
 	aabb_t			aabb;		/* node coordinates expressed in the space of -1.0...1.0 */
+	v2f_t			position;	/* position of node, optionally used to move aabb as a whole */
 	float			alpha;		/* alpha for the texture when composited */
 	double			angle;		/* angle for the texture when composited */
 	unsigned		active:1;	/* node is active */
@@ -182,6 +183,22 @@ void stage_node_get_aabb(const stage_t *stage, stage_node_t *node, aabb_t *res_a
 }
 
 
+/* set the position for a node */
+void stage_node_set_position(const stage_t *stage, stage_node_t *node, float x, float y)
+{
+	node->position.x = x;
+	node->position.y = y;
+}
+
+
+/* get the position for a node */
+void stage_node_get_position(const stage_t *stage, stage_node_t *node, float *res_x, float *res_y)
+{
+	*res_x = node->position.x;
+	*res_y = node->position.y;
+}
+
+
 /* set a node to active (participates in rendering) */
 void stage_node_set_active(const stage_t *stage, stage_node_t *node)
 {
@@ -309,14 +326,14 @@ void stage_fit(const stage_t *stage, int width, int height, int *res_width, int
 }
 
 
-static void aabb_to_rect(const aabb_t *aabb, const SDL_Rect *stage_rect, SDL_Rect *res_rect)
+static void aabb_to_rect(const aabb_t *aabb, const v2f_t *pos, const SDL_Rect *stage_rect, SDL_Rect *res_rect)
 {
 	float	half_w = ((float)stage_rect->w) * .5f, half_h = ((float)stage_rect->h) * .5f;	/* FIXME silly to recompute this repeatedly... */
 
 	res_rect->x = stage_rect->x;
 	res_rect->y = stage_rect->y;
-	res_rect->x += ((float)aabb->min.x) * half_w + half_w;
-	res_rect->y += stage_rect->h - (((float)aabb->max.y) * half_h + half_h);
+	res_rect->x += ((float)aabb->min.x + pos->x) * half_w + half_w;
+	res_rect->y += stage_rect->h - (((float)aabb->max.y + pos->y) * half_h + half_h);
 
 	res_rect->w = (aabb->max.x - aabb->min.x) * half_w;
 	res_rect->h = (aabb->max.y - aabb->min.y) * half_h;
@@ -334,7 +351,7 @@ static void render_nodes(list_head_t *head, SDL_Renderer *renderer, SDL_Rect *de
 			continue;
 
 		/* scale the node's aabb stage coordinates to destination renderer coordinates */
-		aabb_to_rect(&node->aabb, dest_rect, &node_rect);
+		aabb_to_rect(&node->aabb, &node->position, dest_rect, &node_rect);
 
 		/* if we have a cached texture, see if the dimensions changed */
 		if (node->cached.texture &&
@@ -442,7 +459,7 @@ stage_node_t * stage_node_lookup_cartesian(const stage_t *stage, int x, int y)
 			if (!node->active)
 				continue;
 
-			aabb_to_rect(&node->aabb, &rect, &node_rect);
+			aabb_to_rect(&node->aabb, &node->position, &rect, &node_rect);
 			if (x >= node_rect.x && x < node_rect.x + node_rect.w &&
 			    y >= node_rect.y && y < node_rect.y + node_rect.h)
 				return node;