帮忙看看关于Opengl的光照问题

[dukelee]

我在场景中使用了光照，但是光照只照亮了场景的一半，想了很久不知道怎么解决
帮忙看一下，谢谢了，代码如下(只有画图部分的代码)，就是在场景中画了一些网格线，然后在正上方
加了光源还有全局环境光

//Ondraw中的画图程序
         glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	
	GLfloat global_ambient[] = {0.5, 0.5, 0.5, 1.0};
	glLightModelfv(GL_LIGHT_MODEL_AMBIENT, global_ambient);
	glEnable(GL_LIGHTING);
	glTranslatef(0.0f, -1.0f, -8.0f);
	glPushMatrix();

	GLfloat sun_position[] = { 0.0f , 6.0f , 0.0f , 1.0f };//这里是光源的位置，更改Z坐标可以移动光源，但是也只能照到场景的一半，Z<0 的部分是亮的
	GLfloat sun_ambient[] = { 0.0f , 0.0f , 0.0f , 1.0f};
	GLfloat sun_diffuse[] = { 0.8f , 0.8 , 0.8f , 1.0f };
	GLfloat sun_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };
	glLightfv(GL_LIGHT0, GL_POSITION, sun_position);
	glLightfv(GL_LIGHT0, GL_AMBIENT, sun_ambient);
	glLightfv(GL_LIGHT0, GL_DIFFUSE, sun_diffuse);
	glLightfv(GL_LIGHT0, GL_SPECULAR, sun_specular);
	glEnable(GL_LIGHT0);

	//int numtriangles;
	//numtriangles = m_3DObj.m_pFaces.size();
	//GLfloat x_m, y_m, z_m, u_m, v_m;
	GLfloat grid_ambient[] = { 0.5f, 0.5f, 0.5f, 1.0f };
	GLfloat grid_diffuse[] = { 0.8f, 0.8f, 0.8f, 1.0f };
	GLfloat grid_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };
	glMaterialfv(GL_FRONT,GL_SPECULAR,grid_specular);
	glMaterialfv(GL_FRONT,GL_DIFFUSE,grid_diffuse);
	glMaterialfv(GL_FRONT,GL_AMBIENT,grid_ambient);
	glMateriali(GL_FRONT,GL_SHININESS,1);

	GLfloat x_grid, z_grid;//网格线
	for(x_grid = -6.0f; x_grid < 6.0f; x_grid += 0.25f)
	{
		for(z_grid = -6.0f; z_grid < 6.0f; z_grid += 0.25f)
		{
			glBegin(GL_LINE_LOOP);
			glVertex3f(x_grid, 0.0f, z_grid);
			glVertex3f(x_grid, 0.0f, z_grid + 0.25f);
			glVertex3f(x_grid + 0.25f, 0.0f, z_grid + 0.25f);
			glVertex3f(x_grid + 0.25f, 0.0f, z_grid);
			glEnd();
		}
	}
		
	//glEnable(GL_BLEND);//这里是坐标轴线
	//glEnable(GL_LINE_SMOOTH);
	//GLfloat axis_ambient[] = { 0.8f, 0.0f, 0.8f, 1.0f };
	//glMaterialfv(GL_FRONT,GL_AMBIENT,axis_ambient);
	//glLineWidth(2.0f);
	//glBegin(GL_LINES);
	//glVertex3f(-20.0f, 0.0f, 0.0f);
	//glVertex3f(20.0f, 0.0f, 0.0f);
	//glVertex3f(0.0f, 0.0f, 20.0f);
	//glVertex3f(0.0f, 0.0f, -20.0f);
	//glEnd();
	//glLineWidth(1.0f);
	//glDisable(GL_LINE_SMOOTH);
	//glDisable(GL_BLEND);

	glPopMatrix();
	SwapBuffers(wglGetCurrentDC());
	glDisable(GL_LIGHTING);
	glDisable(GL_LIGHT0);

[尹成]

友情支持,三颗心关照，up~up~up~!!

[dukelee]

帮忙看看吧，分不够可以再加，光照这方面感觉没个准头。。。

[zwqxin]

启用光源最好自己加法线.你现在用的是默认法线而已。glNormal系列函数，你学学吧

http://www.owlei.com/DancingWind/Course/Tutorial_07.htm
http://blog.chinaunix.net/u/26313/showart_1663228.html

地板的顶点法线都是向上
glNormal3f(0.0,1.0,0.0);
glVertex3f(x_grid, 0.0f, z_grid);
glNormal3f(0.0,1.0,0.0);
glVertex3f(x_grid, 0.0f, z_grid + 0.25f);
glNormal3f(0.0,1.0,0.0);
glVertex3f(x_grid + 0.25f, 0.0f, z_grid + 0.25f);
glNormal3f(0.0,1.0,0.0);
glVertex3f(x_grid + 0.25f, 0.0f, z_grid);


还有，把glLightfv(GL_LIGHT0, GL_POSITION, sun_position);放在glTranslatef(0.0f, -1.0f, -8.0f);前面，亮一半很可能是因为这个

[dukelee]

试了一下，果然是法向量的问题，确实需要指定法向量
glVertex3f(x_grid, 0.0f, z_grid);
glVertex3f(x_grid, 0.0f, z_grid + 0.25f);
glVertex3f(x_grid + 0.25f, 0.0f, z_grid + 0.25f);
glVertex3f(x_grid + 0.25f, 0.0f, z_grid);
可还是想不明白怎么法向量会在上面的语句中被反向，太感谢了