Android OpenGL ES 开发教程(27)：材质及光照示例

设置物体表面材料(Material)的反光属性（颜色和材质）的方法如下：

public void glMaterialf(int face,int pname,float param)
public void glMaterialfv(int face,int pname,float[] params,int offset)
public void glMaterialfv(int face,int pname,FloatBuffer params)

• face : 在OpenGL ES中只能使用GL_FRONT_AND_BACK，表示修改物体的前面和后面的材质光线属性。
• pname: 参数类型，可以有GL_AMBIENT, GL_DIFFUSE, GL_SPECULAR, GL_EMISSION, GL_SHININESS。这些参数用在光照方程。
• param： 参数的值。

其中GL_AMBIENT,GL_DIFFUSE,GL_SPECULAR ，GL_EMISSION为颜色RGBA值，GL_SHININESS 值可以从0到128，值越大，光的散射越小：

此外，方法glLightModleXX给出了光照模型的参数

public void glLightModelf(int pname,float param)
public void glLightModelfv(int pname,float[] params,int offset)
public void glLightModelfv(int pname,FloatBuffer params)

• pname: 参数类型，可以为GL_LIGHT_MODEL_AMBIENT和GL_LIGHT_MODEL_TWO_SIDE
• params: 参数的值。

最终顶点的颜色由这些参数（光源，材质光学属性，光照模型）综合决定（光照方程计算出）。

下面例子在场景中设置一个白色光源：

public void initScene(GL10 gl){
 float[] amb = { 1.0f, 1.0f, 1.0f, 1.0f, };
 float[] diff = { 1.0f, 1.0f, 1.0f, 1.0f, };
 float[] spec = { 1.0f, 1.0f, 1.0f, 1.0f, };
 float[] pos = { 0.0f, 5.0f, 5.0f, 1.0f, };
 float[] spot_dir = { 0.0f, -1.0f, 0.0f, };
 gl.glEnable(GL10.GL_DEPTH_TEST);
 gl.glEnable(GL10.GL_CULL_FACE);
 
 gl.glEnable(GL10.GL_LIGHTING);
 gl.glEnable(GL10.GL_LIGHT0);
 ByteBuffer abb
 = ByteBuffer.allocateDirect(amb.length*4);
 abb.order(ByteOrder.nativeOrder());
 FloatBuffer ambBuf = abb.asFloatBuffer();
 ambBuf.put(amb);
 ambBuf.position(0);
 
 ByteBuffer dbb
 = ByteBuffer.allocateDirect(diff.length*4);
 dbb.order(ByteOrder.nativeOrder());
 FloatBuffer diffBuf = dbb.asFloatBuffer();
 diffBuf.put(diff);
 diffBuf.position(0);
 
 ByteBuffer sbb
 = ByteBuffer.allocateDirect(spec.length*4);
 sbb.order(ByteOrder.nativeOrder());
 FloatBuffer specBuf = sbb.asFloatBuffer();
 specBuf.put(spec);
 specBuf.position(0);
 
 ByteBuffer pbb
 = ByteBuffer.allocateDirect(pos.length*4);
 pbb.order(ByteOrder.nativeOrder());
 FloatBuffer posBuf = pbb.asFloatBuffer();
 posBuf.put(pos);
 posBuf.position(0);
 
 ByteBuffer spbb
 = ByteBuffer.allocateDirect(spot_dir.length*4);
 spbb.order(ByteOrder.nativeOrder());
 FloatBuffer spot_dirBuf = spbb.asFloatBuffer();
 spot_dirBuf.put(spot_dir);
 spot_dirBuf.position(0);
 
 gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_AMBIENT, ambBuf);
 gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_DIFFUSE, diffBuf);
 gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_SPECULAR, specBuf);
 gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_POSITION, posBuf);
 gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_SPOT_DIRECTION,
 spot_dirBuf);
 gl.glLightf(GL10.GL_LIGHT0, GL10.GL_SPOT_EXPONENT, 0.0f);
 gl.glLightf(GL10.GL_LIGHT0, GL10.GL_SPOT_CUTOFF, 45.0f);
 
 gl.glLoadIdentity();
 GLU.gluLookAt(gl,0.0f, 4.0f, 4.0f, 0.0f, 0.0f, 0.0f,
 0.0f, 1.0f, 0.0f);
 
}

绘制一个球，并使用蓝色材质：

public void drawScene(GL10 gl) {
 super.drawScene(gl);
 
 float[] mat_amb = {0.2f * 0.4f, 0.2f * 0.4f,
 0.2f * 1.0f, 1.0f,};
 float[] mat_diff = {0.4f, 0.4f, 1.0f, 1.0f,};
 float[] mat_spec = {1.0f, 1.0f, 1.0f, 1.0f,};
 
 ByteBuffer mabb
 = ByteBuffer.allocateDirect(mat_amb.length*4);
 mabb.order(ByteOrder.nativeOrder());
 FloatBuffer mat_ambBuf = mabb.asFloatBuffer();
 mat_ambBuf.put(mat_amb);
 mat_ambBuf.position(0);
 
 ByteBuffer mdbb
 = ByteBuffer.allocateDirect(mat_diff.length*4);
 mdbb.order(ByteOrder.nativeOrder());
 FloatBuffer mat_diffBuf = mdbb.asFloatBuffer();
 mat_diffBuf.put(mat_diff);
 mat_diffBuf.position(0);
 
 ByteBuffer msbb
 = ByteBuffer.allocateDirect(mat_spec.length*4);
 msbb.order(ByteOrder.nativeOrder());
 FloatBuffer mat_specBuf = msbb.asFloatBuffer();
 mat_specBuf.put(mat_spec);
 mat_specBuf.position(0);
 
 gl.glMaterialfv(GL10.GL_FRONT_AND_BACK,
 GL10.GL_AMBIENT, mat_ambBuf);
 gl.glMaterialfv(GL10.GL_FRONT_AND_BACK,
 GL10.GL_DIFFUSE, mat_diffBuf);
 gl.glMaterialfv(GL10.GL_FRONT_AND_BACK,
 GL10.GL_SPECULAR, mat_specBuf);
 gl.glMaterialf(GL10.GL_FRONT_AND_BACK,
 GL10.GL_SHININESS, 64.0f);
 
 sphere.draw(gl);
 
}

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