OpenGL之线的连接（CR）

PART ONE

codes.cpp

#include <stdio.h>
#include <GL/glew.h>
#include <GL/freeglut.h>
#include <iostream>
using namespace std;

#define width	222
#define height	207
#define num		3  //顶点计数器

struct Vector3f {
	GLfloat x;
	GLfloat y;
	GLfloat z;
};

struct Color {
	GLubyte r;
	GLubyte g;
	GLubyte b;
	GLubyte a;
};

GLubyte image[height][width][4];

void initLines()
{
	//定义NDC下的顶点数据
	Vector3f points[num]{
		{0.0f,0.0f,0.0f},
		{0.5f,0.0f,0.0f},
		{0.5f,0.5f,0.0f}
	};
	//定义颜色数据
	Color color[num]{
		{255,0,0,0},
		{0,255,0,0},
		{0,0,255,0}
	};

	//将NDC坐标转换成屏幕坐标
	for (int i = 0; i < num; i++){	
		points[i].x = (points[i].x + 1.0f) * (width / 2 - 1);
		points[i].y = (points[i].y + 1.0f) * (height / 2 - 1);
		points[i].z = 0;	//zbuffer统一设置为0
	}

	for (int i = 0; i < num-1; i++){
		//定义线的起点
		int start = i;
		int start_x = (int)points[start].x;
		int start_y = (int)points[start].y;
		//定义线的终点 两两相邻取点
		int end = i + 1;
		int end_x = (int)points[end].x;
		int end_y = (int)points[end].y;

		//保证线起点的坐标(x,y)不大于终点的(x,y)
		if (start_x > end_x) {
			swap(start_x,end_x);
		}
		if (start_y > end_y) {
			swap(start_y, end_y);
		}

		//斜率法画线
		float delta_x = end_x - start_x;
		float delta_y = end_y - start_y;
		//便于算法的实现，将线宽设置为1
		float lineWidth = 1.0f;
		//采用起点的颜色画线
		if (delta_x == 0 || delta_y == 0) {
			for (int y = start_y; y <= end_y; y++) {
				for (int x = start_x; x <= end_x; x++) {
					image[y][x][0] = color[i].r;
					image[y][x][1] = color[i].g;
					image[y][x][2] = color[i].b;
					image[y][x][3] = color[i].a;
				}
			}
		}
		else {
			float gradient = (float)delta_y / delta_x;
			for (int x = start_x; x <= end_x; x++) {
				//直线斜率公式
				int y = (int)(gradient * (x - start_x) + start_y);
				image[y][x][0] = color[i].r;
				image[y][x][1] = color[i].g;
				image[y][x][2] = color[i].b;
				image[y][x][3] = color[i].a;
				 
			}
		}	
	}	
}

void render()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glDrawPixels(width, height, GL_RGBA, GL_UNSIGNED_BYTE, image);
	glutSwapBuffers();
}

int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
	glutInitWindowSize(width, height);
	glutInitWindowPosition(200, 100);
	int id = glutCreateWindow("线的连接");

	GLenum err = glewInit();
	if (err != GLEW_OK) {
		fprintf(stderr, "Error: '%s'\n", glewGetErrorString(err));
		return 1;
	}

	initLines();
	glutDisplayFunc(render);
	glutMainLoop();

	return 0;
}

部分二

代码分下

1、修改顶点计数器num的值为3，则可生成3个顶点。

2、在initPoints()中，初始化3个顶点属性：坐标、颜色（User-Defined：用户自定义）。将顶点按···{i-1:i}，{i:i+1}···的方式构造成点对，{?:?+1}~{start:end}。对点对{start:end}利用“斜率法”构造的线的颜色为起点start.color的颜色。

3、render()函数实现绘制、显示功能。