From 1af3d32d9c0e44c770de442be8dad7be05ae02d4 Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pj@pehjota.net>
Date: Sun, 08 Aug 2021 16:59:35 -0400
Subject: maze: Optionally hide unseen walls

---
(limited to 'src/maze.c')

diff --git a/src/maze.c b/src/maze.c
index 028e940..d991328 100644
--- a/src/maze.c
+++ b/src/maze.c
@@ -24,7 +24,9 @@
 struct mf_maze {
 	int           w;
 	int           h;
+	int           show_all;
 	unsigned int *walls;
+	unsigned int *show;
 	unsigned int *visited;
 };
 
@@ -69,6 +71,47 @@ mf_maze_is_wall(struct mf_maze *m, int x, int y, int dx, int dy)
 		& 1 << (i % (sizeof(*m->walls)*8)));
 }
 
+void
+mf_maze_reveal_wall(struct mf_maze *m, int x, int y, int dx, int dy)
+{
+	int i;
+
+	if (x + dx < 0 || x + dx >= m->w || y + dy < 0 || y + dy >= m->h) {
+		return;
+	}
+
+	if (dx < 0) --x;
+	if (dy < 0) --y;
+	i = y * m->w + x;
+	i *= 2;
+	if (dx == 0) ++i;  /* Moving vertically */
+
+	m->show[i / (sizeof(*m->show)*8)] |= 1 << (i % (sizeof(*m->show)*8));
+}
+
+static int
+_mf_maze_revealed_wall(struct mf_maze *m, int x, int y, int dx, int dy)
+{
+	int i;
+
+	if (m->show_all) {
+		return 1;
+	}
+
+	if (x + dx < 0 || x + dx >= m->w || y + dy < 0 || y + dy >= m->h) {
+		return 1;
+	}
+
+	if (dx < 0) --x;
+	if (dy < 0) --y;
+	i = y * m->w + x;
+	i *= 2;
+	if (dx == 0) ++i;  /* Moving vertically */
+
+	return m->show[i / (sizeof(*m->show)*8)]
+		& 1 << (i % (sizeof(*m->show)*8));
+}
+
 static void
 _mf_maze_visit(struct mf_maze *m, int x, int y)
 {
@@ -128,7 +171,7 @@ _mf_maze_carve(struct mf_maze *m, int x, int y)
 }
 
 struct mf_maze *
-mf_maze_new(int s, int w, int h)
+mf_maze_new(int s, int w, int h, int show_all)
 {
 	struct mf_maze *m;
 	int             x;
@@ -147,19 +190,30 @@ mf_maze_new(int s, int w, int h)
 		free(m);
 		return NULL;
 	}
+	m->show = calloc(
+			(w * h * 2 + sizeof(*m->show)*8 - 1) /
+				(sizeof(*m->show)*8),
+			sizeof(*m->show));
+	if (m->show == NULL) {
+		free(m->walls);
+		free(m);
+		return NULL;
+	}
 	m->visited = calloc(
 			((w+2) * (h+2) + sizeof(*m->visited)*8 - 1) /
 				(sizeof(*m->visited)*8),
 			sizeof(*m->visited));
 	if (m->visited == NULL) {
+		free(m->show);
 		free(m->walls);
 		free(m);
 		return NULL;
 	}
 
 	/* Initialize parameters */
-	m->w = w;
-	m->h = h;
+	m->w        = w;
+	m->h        = h;
+	m->show_all = show_all;
 
 	/* Mark edges as visited */
 	for (x = -1; x <= w; ++x) {
@@ -198,7 +252,8 @@ mf_maze_render(struct mf_maze *m, SDL_Renderer *renderer, SDL_Color *color,
 	}
 	for (y = 0; y < m->h; ++y) {
 		for (x = 0; x < m->w; ++x) {
-			if (y < m->h - 1 && mf_maze_is_wall(m, x, y, 0, 1)) {
+			if (y < m->h - 1 && mf_maze_is_wall(m, x, y, 0, 1) &&
+					_mf_maze_revealed_wall(m, x, y, 0, 1)) {
 				/* Draw h line */
 				if (SDL_RenderDrawLine(renderer,
 							(x  ) * cw, (y+1) * cw,
@@ -211,7 +266,8 @@ mf_maze_render(struct mf_maze *m, SDL_Renderer *renderer, SDL_Color *color,
 					e = -1;
 				}
 			}
-			if (x < m->w - 1 && mf_maze_is_wall(m, x, y, 1, 0)) {
+			if (x < m->w - 1 && mf_maze_is_wall(m, x, y, 1, 0) &&
+					_mf_maze_revealed_wall(m, x, y, 1, 0)) {
 				/* Draw v line */
 				if (SDL_RenderDrawLine(renderer,
 							(x+1) * cw, (y  ) * cw,
@@ -243,6 +299,9 @@ mf_maze_destroy(struct mf_maze **m_p)
 	if (m->walls != NULL) {
 		free(m->walls);
 	}
+	if (m->show != NULL) {
+		free(m->show);
+	}
 	free(m);
 	m = NULL;
 }
--
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