OpenGL超级宝典笔记——光照参数与材料属性

2019独角兽企业重金招聘Python工程师标准>>>

<h3>添加光照</h3> glEnable(GL_LIGHTING); 这个函数调用告诉OpenGL使用材料属性和光照参数去决定每个顶点的颜色值。如果没有开启这个函数，则看到的物体是昏暗的。开启光照后会根据你的材料属性和光照参数计算顶点的颜色值。下图对比未开启光照和开启光照的效果。 <a href="http://static.oschina.net/uploads/img/201310/07213646_TTBF.png"><img title="image" style="border-top: 0px; border-right: 0px; background-image: none; border-bottom: 0px; padding-top: 0px; padding-left: 0px; border-left: 0px; display: inline; padding-right: 0px" border="0" alt="image" src="http://static.oschina.net/uploads/img/201310/07213647_E9ZV.png" width="218" height="217" /></a>（未开启光照） <a href="http://static.oschina.net/uploads/img/201310/07213648_pWop.png"><img title="image" style="border-top: 0px; border-right: 0px; background-image: none; border-bottom: 0px; padding-top: 0px; padding-left: 0px; border-left: 0px; display: inline; padding-right: 0px" border="0" alt="image" src="http://static.oschina.net/uploads/img/201310/07213649_ZT30.png" width="216" height="244" /></a>（开启光照） <h3>设置全局环境光</h3> OpenGL提供了一种全局的环境光。这种光是一种向所有方向均匀发射的光源。它可以照明没有被光源直接照射的物体的背面。 在OpenGL中通过glLightModel这个函数来设置全局环境光。第一个参数是GL_LIGHT_ＭＯDEL_AMBIETN。 <div> <pre id="codeSnippet" class="csharpcode">//明亮的白光 GLfloat ambientLight[] = {1.0f, 1.0f, 1.0f, 1.0f}; //开启光照 glEnable(GL_LIGHTING); //设置全局环境光为白光 glLightModelfv(GL_LIGHT_MODEL_AMBIENT, ambientLight);</pre> </div>

<div>全局环境光照的默认RGBA值是(0.2, 0.2, 0.2, 1.0)，这个值是比较昏暗的。</div>

<h3>设置材料属性</h3>

设置好了全局环境光源后，我们需要为设置材料属性。有两种设置材料属性的方式，第一种是在指定多边形之前调用glMaterial函数。例子：

<div id="codeSnippetWrapper"> <pre id="codeSnippet" class="csharpcode">//灰色的材料属性 GLfloat gray[] = {0.75f, 0.75f, 0.75f, 1.0f}; glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, gray); glBegin(GL_TRIANGLES); glVertex3f(-15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 15.0f, 30.0f); glVertex3f(0.0f, 0.0f, -56.0f); glEnd();</pre> glMaterialfv的第一个参数是指定正面, 反面, 正面和反面。第二个参数是告诉Opengl设置哪个属性。GL_AMBIENT_AND_DIFFUSE指定环境光反射属性和漫反射属性为同一个值。最后一个参数是一个RGBA值的数组。

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<div>在绝大多数情况下，环境光和漫反射光的成分是相同的，除非需要特殊的镜面光的效果。在多边形顶点之前需要调用glMaterial函数，并设置一个包含各种颜色成分的数组。这个操作还是相当繁琐的。下面介绍一种更简单的方式</div>

<div>第二种方法颜色追踪较为简单。使用颜色追踪，可以通过glColor来设置材料属性。第一步启用颜色追踪</div>

<div>glEnable(GL_COLOR_MATERIAL);</div>

<div>然后通过glColorMaterial指定需要颜色追踪的材料属性。下面的例子的设置追踪多边形正面的环境光和漫反射的材料属性。</div>

<div>glColorMaterial(GL_FRONT, GL_AMBIENT_ANDDIFFUSE);</div>

<div>下面的例子使用颜色追踪的方式重写上面的例子：</div>

<div> <pre id="codeSnippet" class="csharpcode">//开启颜色追踪 glEnable(GL_COLOR_MATERIAL); //设置颜色追踪的材料属性以及多边形的面 glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE); //设置颜色 glColor3f(0.75f, 0.75f, 0.75f); glBegin(GL_TRIANGLES); glVertex3f(-15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 15.0f, 30.0f); glVertex3f(0.0f, 0.0f, -56.0f); glEnd(); </pre> </div>

<div>设置环境的例子:</div>

<div id="codeSnippetWrapper"> <pre id="codeSnippet" class="csharpcode">void SetupRC() { GLfloat ambientLight[] = {1.0f, 1.0f, 1.0f, 1.0f}; glEnable(GL_DEPTH_TEST); glEnable(GL_CULL_FACE); glFrontFace(GL_CCW); glEnable(GL_COLOR_MATERIAL); glEnable(GL_LIGHTING); //设置光照模型 glLightModelfv(GL_LIGHT_MODEL_AMBIENT, ambientLight); //设置材料追踪 glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE); glClearColor(0.0f, 0.0f, 05.f,1.0f); } </pre> 开启明亮的环境光效果:</div>

<div>把环境光调成原来的一半的效果:</div>

<div>GLfloat ambientLight[] = {0.5f, 0.5f, 0.5f, 1.0f};</div>

<div id="codeSnippetWrapper"> <pre id="codeSnippet" class="csharpcode">完整的例子： #include "gltools.h" // System and OpenGL Stuff // Rotation amounts static GLfloat xRot = 0.0f; static GLfloat yRot = 0.0f; // Called to draw scene void RenderScene(void) { // Clear the window with current clearing color glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Save matrix state and do the rotation glPushMatrix(); glRotatef(xRot, 1.0f, 0.0f, 0.0f); glRotatef(yRot, 0.0f, 1.0f, 0.0f); glColor3f(1.0f, 1.0f, 1.0f); glBegin(GL_TRIANGLES); //机头 glVertex3f(-15.0f, 0.0f, 30.0f); glVertex3f(15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 0.0f, 60.0f); glColor3f(0.0f, 0.0f, 0.0f); glVertex3f(-15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 0.0f, 60.0f); glVertex3f(0.0f, 15.0f, 30.0f); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(0.0f, 0.0f, 60.0f); glVertex3f(15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 15.0f, 30.0f); //机身 glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(-15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 15.0f, 30.0f); glVertex3f(0.0f, 0.0f, -53.0f); glColor3f(1.0f, 1.0f, 0.0f); glVertex3f(0.0f, 15.0f, 30.0f); glVertex3f(15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 0.0f, -53.0f); glColor3f(0.5f, 0.5f, 0.3f); glVertex3f(15.0f, 0.0f, 30.0f); glVertex3f(-15.0f, 0.0f, 30.0f); glVertex3f(0.0f, 0.0f, -53.0f); //机尾巴 glColor3f(0.3f, 1.0f, 0.2f); glVertex3f(0.0f, 0.0f, -53.0f); glVertex3f(0.0f, 0.0f, -70.0f); glVertex3f(0.0f, 15.0f, -70.0f); glColor3f(0.7f, 0.5f, 0.3f); glVertex3f(-15.0f, 0.0f, -70.0f); glVertex3f(0.0f, 0.0f, -53.0f); glVertex3f(0.0f, 0.0f, -70.0f); glColor3f(0.2f, 0.2f, 0.8f); glVertex3f(15.0f, 0.0f, -70.0f); glVertex3f(0.0f, 0.0f, -70.0f); glVertex3f(0.0f, 0.0f, -53.0f); //由于背面被消除，背面再画一次 glColor3f(0.3f, 1.0f, 0.2f); glVertex3f(0.0f, 0.0f, -70.0f); glVertex3f(0.0f, 0.0f, -53.0f); glVertex3f(0.0f, 15.0f, -70.0f); glColor3f(0.7f, 0.5f, 0.3f); glVertex3f(0.0f, 0.0f, -53.0f); glVertex3f(-15.0f, 0.0f, -70.0f); glVertex3f(0.0f, 0.0f, -70.0f); glColor3f(0.2f, 0.2f, 0.8f); glVertex3f(0.0f, 0.0f, -70.0f); glVertex3f(15.0f, 0.0f, -70.0f); glVertex3f(0.0f, 0.0f, -53.0f); // 左翼 glColor3ub(128,128,128); glVertex3f(0.0f,2.0f,27.0f); glVertex3f(-60.0f, 2.0f, -8.0f); glVertex3f(60.0f, 2.0f, -8.0f); glColor3ub(64,64,64); glVertex3f(60.0f, 2.0f, -8.0f); glVertex3f(0.0f, 7.0f, -8.0f); glVertex3f(0.0f,2.0f,27.0f); glColor3ub(192,192,192); glVertex3f(60.0f, 2.0f, -8.0f); glVertex3f(-60.0f, 2.0f, -8.0f); glVertex3f(0.0f,7.0f,-8.0f); //右翼 glColor3ub(64,64,64); glVertex3f(0.0f,2.0f,27.0f); glVertex3f(0.0f, 7.0f, -8.0f); glVertex3f(-60.0f, 2.0f, -8.0f); glEnd(); glPopMatrix(); // Display the results glutSwapBuffers(); } // This function does any needed initialization on the rendering // context. void SetupRC() { GLfloat ambientLight[] = {0.5f, 0.5f, 0.5f, 1.0f}; glEnable(GL_DEPTH_TEST); // Hidden surface removal glEnable(GL_CULL_FACE); // Do not calculate inside of jet glFrontFace(GL_CCW); // Counter clock-wise polygons face out glEnable(GL_COLOR_MATERIAL); glEnable(GL_LIGHTING); glLightModelfv(GL_LIGHT_MODEL_AMBIENT, ambientLight); glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE); // Nice light blue glClearColor(0.0f, 0.0f, 05.f,1.0f); } void SpecialKeys(int key, int x, int y) { if(key == GLUT_KEY_UP) xRot-= 5.0f; if(key == GLUT_KEY_DOWN) xRot += 5.0f; if(key == GLUT_KEY_LEFT) yRot -= 5.0f; if(key == GLUT_KEY_RIGHT) yRot += 5.0f; if(key > 356.0f) xRot = 0.0f; if(key < -1.0f) xRot = 355.0f; if(key > 356.0f) yRot = 0.0f; if(key < -1.0f) yRot = 355.0f; // Refresh the Window glutPostRedisplay(); } void ChangeSize(int w, int h) { GLfloat nRange = 80.0f; // Prevent a divide by zero if(h == 0) h = 1; // Set Viewport to window dimensions glViewport(0, 0, w, h); // Reset coordinate system glMatrixMode(GL_PROJECTION); glLoadIdentity(); // Establish clipping volume (left, right, bottom, top, near, far) if (w <= h) glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange); else glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } int main(int argc, char* argv[]) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH); glutInitWindowSize(800,600); glutCreateWindow("Jet"); glutReshapeFunc(ChangeSize); glutSpecialFunc(SpecialKeys); glutDisplayFunc(RenderScene); SetupRC(); glutMainLoop(); return 0; } </pre>

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转载于:https://my.oschina.net/sweetdark/blog/167124

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OpenGL超级宝典笔记——光照参数与材料属性

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