add the intersect_poly_line{,seg} helper methods (5ff5a824) · Commits · github_fork / Clip

core/graphics/intersect.cc

+41 −0

Original line number	Diff line number	Diff line
		@@ -168,6 +168,47 @@ bool intersect_lineseg_lineseg(
		return true;
		}

		void intersect_poly_line(
		const Polygon2& p0,
		const vec2& p1,
		const vec2& v1,
		std::vector<vec2>* x) {
		// intersect with each edge of the polygon
		for (size_t i = 0; i < p0.vertices.size(); ++i) {
		Point p;
		auto p_found = intersect_line_lineseg(
		p1,
		v1,
		p0.vertices[i],
		p0.vertices[(i + 1) % p0.vertices.size()],
		&p);

		if (p_found) {
		x->push_back(p);
		}
		}
		}

		void intersect_poly_lineseg(
		const Polygon2& p0,
		const vec2& s1,
		const vec2& e1,
		std::vector<vec2>* x) {
		// intersect with each edge of the polygon
		for (size_t i = 0; i < p0.vertices.size(); ++i) {
		Point p;
		auto p_found = intersect_lineseg_lineseg(
		p0.vertices[i],
		p0.vertices[(i + 1) % p0.vertices.size()],
		s1,
		e1,
		&p);

		if (p_found) {
		x->push_back(p);
		}
		}
		}

		} // namespace fviz

core/graphics/intersect.h

+21 −0

Original line number	Diff line number	Diff line
		@@ -18,6 +18,7 @@
		#include "graphics/color.h"
		#include "graphics/layer.h"
		#include "graphics/geometry.h"
		#include "graphics/polygon.h"
		#include "return_code.h"
		#include "sexpr.h"

		@@ -59,5 +60,25 @@ bool intersect_lineseg_lineseg(
		vec2 e1,
		vec2* p = nullptr);

		/**
		* Given a polygon and an (infinite) line defined by a point on the line p1 and
		* the lines direction v1, compute their points of intersection if any.
		*/
		void intersect_poly_line(
		const Polygon2& p0,
		const vec2& p1,
		const vec2& v1,
		std::vector<vec2>* x);

		/**
		* Given a polygon and a line segement defined by its start and end points of the
		* two line segments s1, e1, compute their points of intersection if any.
		*/
		void intersect_poly_lineseg(
		const Polygon2& p0,
		const vec2& s1,
		const vec2& e1,
		std::vector<vec2>* x);

		} // namespace fviz

core/graphics/polygon.h

0 → 100644

+39 −0

Original line number	Diff line number	Diff line
		/**
		* This file is part of the "fviz" project
		* Copyright (c) 2018 Paul Asmuth
		*
		* Licensed under the Apache License, Version 2.0 (the "License");
		* you may not use this file except in compliance with the License.
		*
		* Unless required by applicable law or agreed to in writing, software
		* distributed under the License is distributed on an "AS IS" BASIS,
		* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
		* See the License for the specific language governing permissions and
		* limitations under the License.
		*/
		#pragma once
		#include <assert.h>
		#include <stdlib.h>
		#include <stdint.h>
		#include <iostream>
		#include "geometry.h"

		namespace fviz {

		/**
		* A polygon in 2D space defined by its vertices. A polygon is always closed;
		* for N vertices in the polygon, the polygon has N edges where one edge goes
		* from the last vertex in the list to the first vertex in the list.
		*
		* Note that polygons can be given in clockwise or counter-clockwise winding
		* order and that they may or may not self-intersect. Methods that work on
		* polygons will usually accept only a subset of these cases.
		*/
		struct Polygon2 {
		std::vector<vec2> vertices;
		};

		std::ostream& operator <<(std::ostream& os, const Polygon2& p);

		} // namespace fviz

core/graphics/shape_hatch.cc

+13 −67

Original line number	Diff line number	Diff line
		@@ -26,6 +26,14 @@ Path shape_hatch(
		auto direction = vec2_from_deg(angle_deg);
		auto ortho = vec2_from_deg(angle_deg + 90);

		Polygon2 clip_poly;
		clip_poly.vertices = {
		{clip.x, clip.y + clip.h},
		{clip.x + clip.w, clip.y + clip.h},
		{clip.x + clip.w, clip.y},
		{clip.x, clip.y},
		};

		Path p;
		for (size_t i = 0; i < 100; ++i) {
		// symmetry around the origin
		@@ -37,76 +45,14 @@ Path shape_hatch(
		// find the intersections with the four borders of the clipping rectangle
		std::vector<Point> intersections;

		// top border
		{
		Point p;
		auto p_found = intersect_line_lineseg(
		o,
		direction,
		{clip.x , clip.y},
		{clip.x + clip.w, clip.y},
		&p);

		if (p_found) {
		intersections.push_back(p);
		}
		}

		// bottom border
		{
		Point p;
		auto p_found = intersect_line_lineseg(
		o,
		direction,
		{clip.x , clip.y + clip.h},
		{clip.x + clip.w, clip.y + clip.h},
		&p);

		if (p_found) {
		intersections.push_back(p);
		}
		}

		// right border
		{
		Point p;
		auto p_found = intersect_line_lineseg(
		o,
		direction,
		{clip.x + clip.w, clip.y},
		{clip.x + clip.w, clip.y + clip.h},
		&p);

		if (p_found) {
		intersections.push_back(p);
		}
		}

		// left border
		{
		Point p;
		auto p_found = intersect_line_lineseg(
		intersect_poly_line(
		clip_poly,
		o,
		direction,
		{clip.x, clip.y},
		{clip.x, clip.y + clip.h},
		&p);

		if (p_found) {
		intersections.push_back(p);
		}
		}
		&intersections);

		// stroke line between edge points
		if (intersections.size() >= 2) {
		auto line_max = vec2_mul(
		vec2_normalize(vec2_sub(intersections[0], intersections[1])),
		vec2_magnitude({clip.w, clip.h}));

		// double the line length to make sure there are no gaps
		intersections[0] = vec2_add(intersections[0], line_max);
		intersections[1] = vec2_sub(intersections[1], line_max);

		p.moveTo(intersections[0].x, clip.h - intersections[0].y);
		p.lineTo(intersections[1].x, clip.h - intersections[1].y);
		}

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