added BlendSpace1D editor plugin

This commit also fixes a crash in the BlendSpace2D as well as correct
the drawing of the x-zero indicator in the BlendSpace2D editor plugin.

scene/animation/animation_blend_space_1d.h

@@ -0,0 +1,68 @@
+#ifndef ANIMATION_BLEND_SPACE_1D_H
+#define ANIMATION_BLEND_SPACE_1D_H
+
+#include "scene/animation/animation_graph_player.h"
+
+class AnimationNodeBlendSpace1D : public AnimationRootNode {
+	GDCLASS(AnimationNodeBlendSpace1D, AnimationRootNode)
+
+	enum {
+		MAX_BLEND_POINTS = 64
+	};
+
+	struct BlendPoint {
+		Ref<AnimationRootNode> node;
+		float position;
+	};
+
+	BlendPoint blend_points[MAX_BLEND_POINTS];
+	int blend_points_used;
+
+	float blend_pos;
+
+	float max_space;
+	float min_space;
+
+	float snap;
+
+	String value_label;
+
+	void _add_blend_point(int p_index, const Ref<AnimationRootNode> &p_node);
+
+protected:
+	virtual void _validate_property(PropertyInfo &property) const;
+	static void _bind_methods();
+
+public:
+	void add_blend_point(const Ref<AnimationRootNode> &p_node, float p_position, int p_at_index = -1);
+	void set_blend_point_position(int p_point, float p_position);
+	void set_blend_point_node(int p_point, const Ref<AnimationRootNode> &p_node);
+
+	float get_blend_point_position(int p_point) const;
+	Ref<AnimationRootNode> get_blend_point_node(int p_point) const;
+	void remove_blend_point(int p_point);
+	int get_blend_point_count() const;
+
+	void set_min_space(float p_min);
+	float get_min_space() const;
+
+	void set_max_space(float p_max);
+	float get_max_space() const;
+
+	void set_snap(float p_snap);
+	float get_snap() const;
+
+	void set_blend_pos(float p_pos);
+	float get_blend_pos() const;
+
+	void set_value_label(const String &p_label);
+	String get_value_label() const;
+
+	float process(float p_time, bool p_seek);
+	String get_caption() const;
+
+	AnimationNodeBlendSpace1D();
+	~AnimationNodeBlendSpace1D();
+};
+
+#endif // ANIMATION_BLEND_SPACE_1D_H