【OpenGL】鼠标控制旋转（四）

首先声明自己是这方面的小白，希望大神可以对有问题以及可以优化的地方提出来。也欢迎指出不足和吐槽。希望帮到小白。

自己参考得比较多的网站是这个：
http://www.cppblog.com/doing5552/archive/2009/01/08/71532.html

所有代码都可以去github免费下载（不怎么喜欢CSDN的积分下载）：
https://github.com/Iamttp/OpenGLTest

不多废话，好先上这一节的效果图。

#include <gl/glut.h>
#include <iostream>

bool mouseDown = false;

float xrot = 0.0f;
float yrot = 0.0f;

float xdiff = 0.0f;
float ydiff = 0.0f;

// 绘制正方体
void drawBox() {
	glBegin(GL_QUADS);

	glColor3f(1.0f, 0.0f, 0.0f);
	// FRONT
	glVertex3f(-0.5f, -0.5f, 0.5f);
	glVertex3f(0.5f, -0.5f, 0.5f);
	glVertex3f(0.5f, 0.5f, 0.5f);
	glVertex3f(-0.5f, 0.5f, 0.5f);
	// BACK
	glVertex3f(-0.5f, -0.5f, -0.5f);
	glVertex3f(-0.5f, 0.5f, -0.5f);
	glVertex3f(0.5f, 0.5f, -0.5f);
	glVertex3f(0.5f, -0.5f, -0.5f);

	glColor3f(0.0f, 1.0f, 0.0f);
	// LEFT
	glVertex3f(-0.5f, -0.5f, 0.5f);
	glVertex3f(-0.5f, 0.5f, 0.5f);
	glVertex3f(-0.5f, 0.5f, -0.5f);
	glVertex3f(-0.5f, -0.5f, -0.5f);
	// RIGHT
	glVertex3f(0.5f, -0.5f, -0.5f);
	glVertex3f(0.5f, 0.5f, -0.5f);
	glVertex3f(0.5f, 0.5f, 0.5f);
	glVertex3f(0.5f, -0.5f, 0.5f);

	glColor3f(0.0f, 0.0f, 1.0f);
	// TOP
	glVertex3f(-0.5f, 0.5f, 0.5f);
	glVertex3f(0.5f, 0.5f, 0.5f);
	glVertex3f(0.5f, 0.5f, -0.5f);
	glVertex3f(-0.5f, 0.5f, -0.5f);
	// BOTTOM
	glVertex3f(-0.5f, -0.5f, 0.5f);
	glVertex3f(-0.5f, -0.5f, -0.5f);
	glVertex3f(0.5f, -0.5f, -0.5f);
	glVertex3f(0.5f, -0.5f, 0.5f);
	glEnd();
}

// 绘制函数
void display() {
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glLoadIdentity();

	gluLookAt(
		0.0f, 0.0f, 3.0f,
		0.0f, 0.0f, 0.0f,
		0.0f, 1.0f, 0.0f);

	// 实现鼠标旋转的核心
	glRotatef(xrot, 1.0f, 0.0f, 0.0f);
	glRotatef(yrot, 0.0f, 1.0f, 0.0f);

	drawBox();

	glFlush();
	glutSwapBuffers();
}

void resize(int w, int h) {
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	glViewport(0, 0, w, h);

	gluPerspective(45.0f, 1.0f * w / h, 1.0f, 100.0f);

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

// 鼠标事件
void mouse(int button, int state, int x, int y) {
	if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
		mouseDown = true;
		xdiff = x - yrot;
		ydiff = -y + xrot;
		std::cout << "xdiff:" << xdiff << "\tydiff" << ydiff << std::endl;
	}
	else
		mouseDown = false;
}

// 鼠标移动事件
void mouseMotion(int x, int y) {
	if (mouseDown) {
		yrot = x - xdiff;
		xrot = y + ydiff;
		std::cout << "yrot:" << yrot << "\txrot" << xrot << std::endl;

		glutPostRedisplay();
	}
}

int main(int argc, char* argv[]) {
	glutInit(&argc, argv);

	glutInitWindowPosition(50, 50);
	glutInitWindowSize(500, 500);

	glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);

	glutCreateWindow("demo");

	glutDisplayFunc(display);
	glutMouseFunc(mouse);
	glutMotionFunc(mouseMotion);
	glutReshapeFunc(resize);

	glClearColor(0.93f, 0.93f, 0.93f, 0.0f);

	glEnable(GL_DEPTH_TEST);
	glDepthFunc(GL_LEQUAL);
	glClearDepth(1.0f);

	glutMainLoop();
	return 0;
}

可以看到代码非常的简洁，这是根据国外的一个示例代码缩减的。关键就是并不是改变了摄像头的视角（gluLookAt）,而是直接在绘制之前就旋转坐标系，让之后绘制的东西都直接旋转了。让我们看起来像摄像头视角在动（我只能说真cool）。

OpenGL专栏： https://blog.csdn.net/qq_40515692/article/details/103938499