OpenGL超級寶典筆記——光照參數與材料屬性

時間 2019-11-13

標籤 opengl 超級寶典筆記光照參數材料屬性简体版

原文原文鏈接

<h3>添加光照</h3> glEnable(GL_LIGHTING); 這個函數調用告訴OpenGL使用材料屬性和光照參數去決定每一個頂點的顏色值。若是沒有開啓這個函數，則看到的物體是昏暗的。開啓光照後會根據你的材料屬性和光照參數計算頂點的顏色值。下圖對比未開啓光照和開啓光照的效果。 <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>（未開啓光照） <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>（開啓光照） <h3>設置全局環境光</h3> OpenGL提供了一種全局的環境光。這種光是一種向全部方向均勻發射的光源。它能夠照明沒有被光源直接照射的物體的背面。 在OpenGL中經過glLightModel這個函數來設置全局環境光。第一個參數是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}; //開啓光照 glEnable(GL_LIGHTING); //設置全局環境光爲白光 glLightModelfv(GL_LIGHT_MODEL_AMBIENT, ambientLight);</pre> </div>數組

<div>全局環境光照的默認RGBA值是(0.2, 0.2, 0.2, 1.0)，這個值是比較昏暗的。</div>app

<div> </div>ide

<h3>設置材料屬性</h3>函數

設置好了全局環境光源後，咱們須要爲設置材料屬性。有兩種設置材料屬性的方式，第一種是在指定多邊形以前調用glMaterial函數。例子：oop

<div id="codeSnippetWrapper"> <pre id="codeSnippet" class="csharpcode">//灰色的材料屬性 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的第一個參數是指定正面, 反面, 正面和反面。第二個參數是告訴Opengl設置哪一個屬性。GL_AMBIENT_AND_DIFFUSE指定環境光反射屬性和漫反射屬性爲同一個值。最後一個參數是一個RGBA值的數組。spa

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<div>在絕大多數狀況下，環境光和漫反射光的成分是相同的，除非須要特殊的鏡面光的效果。在多邊形頂點以前須要調用glMaterial函數，並設置一個包含各類顏色成分的數組。這個操做仍是至關繁瑣的。下面介紹一種更簡單的方式</div>code

<div> </div>ip

<div>第二種方法顏色追蹤較爲簡單。使用顏色追蹤，能夠經過glColor來設置材料屬性。第一步啓用顏色追蹤</div>ci

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

<div>而後經過glColorMaterial指定須要顏色追蹤的材料屬性。下面的例子的設置追蹤多邊形正面的環境光和漫反射的材料屬性。</div>

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

<div>下面的例子使用顏色追蹤的方式重寫上面的例子：</div>

<div> <pre id="codeSnippet" class="csharpcode">//開啓顏色追蹤 glEnable(GL_COLOR_MATERIAL); //設置顏色追蹤的材料屬性以及多邊形的面 glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE); //設置顏色 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>設置環境的例子:</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); //設置光照模型 glLightModelfv(GL_LIGHT_MODEL_AMBIENT, ambientLight); //設置材料追蹤 glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE); glClearColor(0.0f, 0.0f, 05.f,1.0f); } </pre> 開啓明亮的環境光效果:</div>

<div>把環境光調成原來的一半的效果:</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); //機頭 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); //機身 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); //機尾巴 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); //因爲背面被消除，背面再畫一次 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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