Merge pull request #75 from goostengine/bresenham-line

Implement Bresenham line algorithm in `GoostGeometry2D`

core/math/2d/geometry/goost_geometry_2d.cpp

@@ -235,3 +235,43 @@ Vector<Point2> GoostGeometry2D::circle(real_t p_radius, real_t p_max_error) {
 
 	return regular_polygon(vertex_count, p_radius); // vertex count == edge count
 }
+
+// Implementation borrowed from `TileMap` editor plugin:
+// https://github.com/godotengine/godot/blob/0d819ae5f5/editor/plugins/tile_map_editor_plugin.cpp#L982-L1023
+//
+Vector<Point2i> GoostGeometry2D::bresenham_line(const Point2i &p_start, const Point2i &p_end) {
+	Vector<Point2i> points;
+
+	real_t dx = ABS(p_end.x - p_start.x);
+	real_t dy = ABS(p_end.y - p_start.y);
+
+	int x = p_start.x;
+	int y = p_start.y;
+
+	int sx = p_start.x > p_end.x ? -1 : 1;
+	int sy = p_start.y > p_end.y ? -1 : 1;
+
+	if (dx > dy) {
+		real_t err = dx / 2;
+		for (; x != p_end.x; x += sx) {
+			points.push_back(Point2i(x, y));
+			err -= dy;
+			if (err < 0) {
+				y += sy;
+				err += dx;
+			}
+		}
+	} else {
+		real_t err = dy / 2;
+		for (; y != p_end.y; y += sy) {
+			points.push_back(Point2i(x, y));
+			err -= dx;
+			if (err < 0) {
+				x += sx;
+				err += dy;
+			}
+		}
+	}
+	points.push_back(Point2i(x, y));
+	return points;
+}

core/math/2d/geometry/goost_geometry_2d.h

@@ -32,9 +32,10 @@ class GoostGeometry2D {
 	// Returns 0 if false, +1 if true, -1 if point is exactly on the polygon's boundary.
 	static int point_in_polygon(const Point2 &p_point, const Vector<Point2> &p_polygon);
 
-	/* Polygon/shapes generation methods */
+	/* Polygon/primitives generation methods */
 	static Vector<Point2> regular_polygon(int p_edge_count, real_t p_size);
 	static Vector<Point2> circle(real_t p_radius, real_t p_max_error = 0.25);
+	static Vector<Point2i> bresenham_line(const Point2i &p_start, const Point2i &p_end);
 };
 
 #endif // GOOST_GEOMETRY_2D_H

core/math/2d/geometry/goost_geometry_2d_bind.cpp

@@ -134,6 +134,16 @@ Vector<Point2> _GoostGeometry2D::circle(real_t p_radius, real_t p_max_error) con
 	return GoostGeometry2D::circle(p_radius, p_max_error);
 }
 
+// Note: this can be converted to use `Vector2i` in Godot 4.x.
+Vector<Point2> _GoostGeometry2D::bresenham_line(const Point2 &p_start, const Point2 &p_end) const {
+	const Vector<Point2i> &line = GoostGeometry2D::bresenham_line(p_start, p_end);
+	Vector<Point2> ret;
+	for (int i = 0; i < line.size(); ++i) {
+		ret.push_back(line[i]);
+	}
+	return ret;
+}
+
 void _GoostGeometry2D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("merge_polygons", "polygon_a", "polygon_b"), &_GoostGeometry2D::merge_polygons);
 	ClassDB::bind_method(D_METHOD("clip_polygons", "polygon_a", "polygon_b"), &_GoostGeometry2D::clip_polygons);
@@ -159,6 +169,7 @@ void _GoostGeometry2D::_bind_methods() {
 
 	ClassDB::bind_method(D_METHOD("regular_polygon", "sides", "size"), &_GoostGeometry2D::regular_polygon);
 	ClassDB::bind_method(D_METHOD("circle", "radius", "max_error"), &_GoostGeometry2D::circle, DEFVAL(0.25));
+	ClassDB::bind_method(D_METHOD("bresenham_line", "start", "end"), &_GoostGeometry2D::bresenham_line);
 }
 
 _GoostGeometry2D::_GoostGeometry2D() {

core/math/2d/geometry/goost_geometry_2d_bind.h

@@ -40,6 +40,7 @@ class _GoostGeometry2D : public Object {
 
 	Vector<Point2> regular_polygon(int p_edge_count, real_t p_size) const;
 	Vector<Point2> circle(real_t p_radius, real_t p_max_error) const;
+	Vector<Point2> bresenham_line(const Point2 &p_start, const Point2 &p_end) const;
 
 	_GoostGeometry2D();
 };

doc/GoostGeometry2D.xml

@@ -20,6 +20,17 @@
 				Computes the axis-aligned bounding rectangle of given points.
 			</description>
 		</method>
+		<method name="bresenham_line" qualifiers="const">
+			<return type="PoolVector2Array">
+			</return>
+			<argument index="0" name="start" type="Vector2">
+			</argument>
+			<argument index="1" name="end" type="Vector2">
+			</argument>
+			<description>
+				Returns an array of 2D-dimensional raster coordinates going through a segment determined by [code]start[/code] and [code]end[/code] points. The line is a close approximation to a straight line between those points.
+			</description>
+		</method>
 		<method name="circle" qualifiers="const">
 			<return type="PoolVector2Array">
 			</return>

tests/project/goost/core/math/2d/geometry/test_geometry_2d.gd

@@ -127,3 +127,61 @@ func test_regular_polygon():
 func test_circle():
 	solution = GoostGeometry2D.circle(SIZE, 0.25)
 	assert_eq(solution.size(), 32)
+
+
+func test_bresenham_line():
+	var line = GoostGeometry2D.bresenham_line(Vector2(0, 0), Vector2(5, 0))
+	assert_eq(line.size(), 6)
+	for x in 6:
+		assert_eq(line[x], Vector2(x, 0))
+
+	line = GoostGeometry2D.bresenham_line(Vector2(0, 0), Vector2(-10, 0))
+	assert_eq(line.size(), 11)
+	for x in 11:
+		assert_eq(line[x], Vector2(-x, 0))
+
+	line = GoostGeometry2D.bresenham_line(Vector2(0, 0), Vector2(0, 5))
+	assert_eq(line.size(), 6)
+	for x in 6:
+		assert_eq(line[x], Vector2(0, x))
+
+	line = GoostGeometry2D.bresenham_line(Vector2(0, 0), Vector2(0, -10))
+	assert_eq(line.size(), 11)
+	for x in 11:
+		assert_eq(line[x], Vector2(0, -x))
+
+	line = GoostGeometry2D.bresenham_line(Vector2(-5, -5), Vector2(5, 5))
+	assert_eq(line.size(), 11)
+	assert_eq(line[0], Vector2(-5, -5))
+	assert_eq(line[5], Vector2(0, 0))
+	assert_eq(line[10], Vector2(5, 5))
+
+	line = GoostGeometry2D.bresenham_line(Vector2(5, -5), Vector2(-5, 5))
+	assert_eq(line.size(), 11)
+	assert_eq(line[0], Vector2(5, -5))
+	assert_eq(line[5], Vector2(0, 0))
+	assert_eq(line[10], Vector2(-5, 5))
+
+	line = GoostGeometry2D.bresenham_line(Vector2(5, -5), Vector2(-5, 5))
+	assert_eq(line.size(), 11)
+	assert_eq(line[0], Vector2(5, -5))
+	assert_eq(line[5], Vector2(0, 0))
+	assert_eq(line[10], Vector2(-5, 5))
+
+	line = GoostGeometry2D.bresenham_line(Vector2(-5, -5), Vector2(10, 3))
+	assert_eq(line[0], Vector2(-5, -5))
+	assert_eq(line[1], Vector2(-4, -4))
+	assert_eq(line[2], Vector2(-3, -4))
+	assert_eq(line[3], Vector2(-2, -3))
+	assert_eq(line[4], Vector2(-1, -3))
+	assert_eq(line[5], Vector2(0, -2))
+	assert_eq(line[6], Vector2(1, -2))
+	assert_eq(line[7], Vector2(2, -1))
+	assert_eq(line[8], Vector2(3, -1))
+	assert_eq(line[9], Vector2(4, 0))
+	assert_eq(line[10], Vector2(5, 0))
+	assert_eq(line[11], Vector2(6, 1))
+	assert_eq(line[12], Vector2(7, 1))
+	assert_eq(line[13], Vector2(8, 2))
+	assert_eq(line[14], Vector2(9, 2))
+	assert_eq(line[15], Vector2(10, 3))