【OpenGL】鼠標控制旋轉（四）

首先聲明自己是這方面的小白，希望大神可以對有問題以及可以優化的地方提出來。也歡迎指出不足和吐槽。希望幫到小白。

自己參考得比較多的網站是這個：
http://www.cppblog.com/doing5552/archive/2009/01/08/71532.html

所有代碼都可以去github免費下載（不怎麼喜歡CSDN的積分下載）：
https://github.com/Iamttp/OpenGLTest

不多廢話，好先上這一節的效果圖。

#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;

// 繪製正方體
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();
}

// 繪製函數
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);

	// 實現鼠標旋轉的核心
	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();
}

// 鼠標事件
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;
}

// 鼠標移動事件
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;
}

可以看到代碼非常的簡潔，這是根據國外的一個示例代碼縮減的。關鍵就是並不是改變了攝像頭的視角（gluLookAt）,而是直接在繪製之前就旋轉座標系，讓之後繪製的東西都直接旋轉了。讓我們看起來像攝像頭視角在動（我只能說真cool）。