渲染管线一般是由显示芯片GPU内部处理图形信号的并行处理单元组成，这些并行处理单元之间是独立的，从另一个角度看，渲染管线实际上也是一系列绘制过程，这一系列过程的输入是待绘制物体的相关描述信息，输出的是要显示的图像帧数据。
OpenGL ES管线主要包括：
读取顶点数据—>顶点着色器—>组装图元—>光栅化图元—>片元着色器—>写入帧缓冲区—>显示到屏幕上
在OpenGL ES2.0中主要的两个部分就是上面的可编程顶点着色器和片段着色器。学习OpenGL ES主要是要了解渲染管线，了解CPU的渲染过程，主要编程工作在于顶点着色器和片元着色器的编写。
绘制一个六边形
效果如图所示
六边形类
public class SixShape {
private FloatBuffer mVertexBuffer;
private FloatBuffer mColorBuffer;
private int mProgram;
private int mPositionHandle;
private int mColorHandle;
private int muMVPMatrixHandle;
public SixShape(float r) {
initVetexData(r);
}
public void initVetexData(float r) {
// 初始化顶点坐标
float[] vertexArray = new float[8*3];
// 初始化顶点颜色
float[] colorArray=new float[8*4];
int j = 0, k = 0;
vertexArray[j++] = 0;
vertexArray[j++] = 0;
vertexArray[j++] = 0;
colorArray[k++] = 1;
colorArray[k++] = 1;
colorArray[k++] = 1;
colorArray[k++] = 0;
for (int angle = 0; angle <= 360; angle += 60) {
vertexArray[j++] = (float) (r*Math.cos(Math.toRadians(angle)));
vertexArray[j++] = (float) (r*Math.sin(Math.toRadians(angle)));
vertexArray[j++] = 0;
colorArray[k++] = 1;
colorArray[k++] = 0;
colorArray[k++] = 0;
colorArray[k++] = 0;
}
ByteBuffer buffer = ByteBuffer.allocateDirect(vertexArray.length * 4);
buffer.order(ByteOrder.nativeOrder());
mVertexBuffer = buffer.asFloatBuffer();
mVertexBuffer.put(vertexArray);
mVertexBuffer.position(0);
ByteBuffer cbb=ByteBuffer.allocateDirect(colorArray.length*4);
cbb.order(ByteOrder.nativeOrder());
mColorBuffer=cbb.asFloatBuffer();
mColorBuffer.put(colorArray);
mColorBuffer.position(0);
int vertexShader = loaderShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
int fragmentShader = loaderShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
mProgram = GLES20.glCreateProgram();
GLES20.glAttachShader(mProgram, vertexShader);
GLES20.glAttachShader(mProgram, fragmentShader);
GLES20.glLinkProgram(mProgram);
mPositionHandle = GLES20.glGetAttribLocation(mProgram, "aPosition");
mColorHandle = GLES20.glGetAttribLocation(mProgram, "aColor");
muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
}
public void draw(float[] mvpMatrix) {
GLES20.glUseProgram(mProgram);
// 将顶点数据传递到管线，顶点着色器
GLES20.glVertexAttribPointer(mPositionHandle, 3, GLES20.GL_FLOAT, false, 3 * 4, mVertexBuffer);
// 将顶点颜色传递到管线，顶点着色器
GLES20.glVertexAttribPointer(mColorHandle, 4, GLES20.GL_FLOAT, false,4*4, mColorBuffer);
// 将变换矩阵传递到管线
GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mvpMatrix, 0);
GLES20.glEnableVertexAttribArray(mPositionHandle);
GLES20.glEnableVertexAttribArray(mColorHandle);
// 绘制图元
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 8);
}
private int loaderShader(int type, String shaderCode) {
int shader = GLES20.glCreateShader(type);
GLES20.glShaderSource(shader, shaderCode);
GLES20.glCompileShader(shader);
return shader;
}
private String vertexShaderCode = "uniform mat4 uMVPMatrix;"
+ "attribute vec3 aPosition;"
+ "attribute vec4 aColor;"
+ "varying vec4 aaColor;"
+ "void main(){"
+ "gl_Position = uMVPMatrix * vec4(aPosition,1);"
+ "aaColor = aColor;"
+ "}";
private String fragmentShaderCode = "precision mediump float;"
+ "varying vec4 aaColor;"
+ "void main(){"
+ "gl_FragColor = aaColor;"
+ "}";
}
六边形View
public class SixView extends GLSurfaceView{
public SixView(Context context) {
super(context);
setEGLContextClientVersion(2);
setRenderer(new MyRender());
}
class MyRender implements GLSurfaceView.Renderer {
private SixShape circle;
@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1);
circle = new SixShape(0.5f);
GLES20.glEnable(GLES20.GL_DEPTH_TEST);
}
// 投影矩阵
private final float[] mProjectionMatrix = new float[16];
// 视图矩阵
private final float[] mViewMatrix = new float[16];
// 模型矩阵
private final float[] mMMatrix = new float[16];
private final float[] mViewProjectionMatrix = new float[16];
private final float[] mMVPMatrix = new float[16];
@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
GLES20.glViewport(0, 0, width, height);
float ratio= (float) width / height;
// 设置正交投影
Matrix.orthoM(mProjectionMatrix, 0, -ratio, ratio, -1, 1, 0, 5);
// 设置视图矩阵
Matrix.setLookAtM(mViewMatrix, 0, 0, 0, 2, 0, 0, 0, 0, 1, 0);
}
@Override
public void onDrawFrame(GL10 gl) {
GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);
Matrix.multiplyMM(mViewProjectionMatrix, 0, mProjectionMatrix, 0, mViewMatrix, 0);
// 设置模型矩阵
Matrix.setIdentityM(mMMatrix, 0);
Matrix.translateM(mMMatrix,0,0,0,1);
Matrix.rotateM(mMMatrix, 0, 30, 0, 0, 1);
Matrix.multiplyMM(mMVPMatrix, 0, mViewProjectionMatrix, 0, mMMatrix, 0);
circle.draw(mMVPMatrix);
}
}
}
接下来在Activity中就可以使用这个View了。上面的例子虽然简单，但是包括了使用OpenGL ES编程的主要流程，包括生成顶点数据，编写顶点着色器，片元着色器，传递数据给顶点/片元着色器，这里最主要的就是着色器语言。此外包括投影，平移，旋转等操作。在后面会详细学习每个细节以及上面例子没有涉及到的光照，纹理等OpenGL的知识。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。
