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@@ -1,12 +1,12 @@
 # mz_square_cells
 
-This function returns cell data of a square maze. The data is a list of cells. A cell has the data structure `[x, y, wallType]`. `x` and `y` are 0-based. `x` means x-th column and `y` means y-th row for a cell. The value of `type` can be `0`, `1`, ``2`, `3` or `4`. Setting them to constants is convenient.
+This function returns cell data of a square maze. The data is a list of cells. A cell has the data structure `[x, y, type]`. `x` and `y` are 0-based. `x` means the x-th column and `y` means y-th row for a cell. The value of `type` can be `0`, `1`, ``2`, `3` or `4`. Setting them to constants is convenient.
 
-	NO_WALL = 0;       
-	TOP_WALL = 1;    
-	RIGHT_WALL = 2;    
-	TOP_RIGHT_WALL = 3; 
-	MASK = 4;
+	NO_WALL = 0;          // the cell has no wall
+	TOP_WALL = 1;         // the cell has a top wall
+	RIGHT_WALL = 2;       // the cell has a right wall
+	TOP_RIGHT_WALL = 3;   // the cell has a top wall and a right wall
+	MASK = 4;             // the cell is masked.
 
 The cell data is seperated from views. You can use cell data to construct [different types of mazes](https://www.thingiverse.com/justinsdk/collections/maze-generator).
 
diff --git a/docs/lib3x-mz_theta_cells.md b/docs/lib3x-mz_theta_cells.md
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+# mz_theta_cells
+
+This function returns cell data of a theta maze. The data is a two-dimensional list with different row lengths. A cell has the data structure `[ri, ci, type]`. `ri` and `ci` are 0-based. `ri` means the ri-th ring and `ci` means the ci-th (counter-clockwise) cell of the ring. 
+
+![mz_theta_cells](images/lib3x-mz_theta_cells-1.JPG)
+
+The value of `type` is the wall type of the cell. It can be `0`, `1`, ``2` or `3`. Setting them to constants is convenient.
+
+	NO_WALL = 0;           // the cell has no wall
+	INWARD_WALL = 1;       // the cell has an inward wall
+	CCW_WALL = 2;          // the cell has a counter-clockwise wall
+	INWARD_CCW_WALL = 3;   // the cell has an inward wall and a clockwise wall
+
+![mz_theta_cells](images/lib3x-mz_theta_cells-2.JPG)
+
+**Since:** 3.0
+
+## Parameters
+rows, begining_columns
+- `rows` : The number of rings.
+- `beginning_number` : The number of cells in the first row.
+- `start` : The start point to travel the maze. Default to `[0, 0]`.
+- `seed` : The maze is traveling randomly. Use `seed` to initialize the pseudorandom number generator.
+
+## Examples
+    
+	use <maze/mz_theta_cells.scad>;
+	use <hull_polyline2d.scad>;
+
+	rows = 8;
+	beginning_number = 8;
+	cell_width = 10;
+	wall_thickness = 2;
+
+	NO_WALL = 0;           
+	INWARD_WALL = 1;      
+	CCW_WALL = 2;         
+	INWARD_CCW_WALL = 3;   
+
+	function vt_from_angle(theta, r) = [r * cos(theta), r * sin(theta)];
+
+	maze = mz_theta_cells(rows, beginning_number);
+
+	// draw cell walls
+	for(rows = maze) {
+		for(cell = rows) {
+			ri = cell[0];
+			ci = cell[1];
+			type = cell[2];
+			thetaStep = 360 / len(maze[ri]);
+			innerR = (ri + 1) * cell_width;
+			outerR = (ri + 2) * cell_width;
+			theta1 = thetaStep * ci;
+			theta2 = thetaStep * (ci + 1);
+			
+			innerVt1 = vt_from_angle(theta1, innerR);
+			innerVt2 = vt_from_angle(theta2, innerR);
+			outerVt2 = vt_from_angle(theta2, outerR);
+			
+			if(type == INWARD_WALL || type == INWARD_CCW_WALL) {
+				hull_polyline2d([innerVt1, innerVt2], width = wall_thickness);
+			}
+
+			if(type == CCW_WALL || type == INWARD_CCW_WALL) {
+				hull_polyline2d([innerVt2, outerVt2], width = wall_thickness);
+			}
+		} 
+	}
+
+    // outmost walls
+	thetaStep = 360 / len(maze[rows - 1]);
+	r = cell_width * (rows + 1);
+	for(theta = [0:thetaStep:360 - thetaStep]) {
+		vt1 = vt_from_angle(theta, r);
+		vt2 = vt_from_angle(theta + thetaStep, r);
+		hull_polyline2d([vt1, vt2], width = wall_thickness);
+	} 
+
+![mz_theta_cells](images/lib3x-mz_theta_cells-3.JPG)
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