Android OpenGL教程 二 2D形状画画

Posted 2020-10-22

首先画个三角形

    private float[] mTriangleArray={
            0.0f,1.0f,0.0f,
            1.0f,-1.0f,0.0f,
            -1.0f,-1.0f,0.0f
    };

gl.glDrawArrays(GL10.GL_TRIANGLES, 0, mTriangleArray.length/3);

然后画个两个三角形拼成一个正方形，把之前的坐标换一下就好了

    private float[] mTriangleArray={
            1.0f,1.0f,0.0f,
            1.0f,-1.0f,0.0f,
            -1.0f,-1.0f,0.0f,
            -1.0f,-1.0f,0.0f,
            -1.0f,1.0f,0.0f,
            1.0f,1.0f,0.0f
    };

看来glDrawArrays是三个三个坐标来画的

我现在使用glDrawElements这个函数来画正方形，这函数不仅可以画多方形，而且还可以画3D

    private float[] mTriangleArray={
            1.0f,1.0f,0.0f,
            1.0f,-1.0f,0.0f,
            -1.0f,-1.0f,0.0f,
            -1.0f,1.0f,0.0f
    };

    private float[] mColor ={
            1.0f,0.0f,0.0f,1.0f,
            1.0f,0.0f,0.0f,1.0f,
            1.0f,0.0f,0.0f,1.0f,
            1.0f,0.0f,0.0f,1.0f
    };
    private byte[] cubeFacets = new byte[]{
            0, 1, 2,
            0, 2, 3
    };

        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mTriangleBuffer);
        gl.glColorPointer(4, GL10.GL_FLOAT, 0, mColorBuffer);
        gl.glDrawElements(GL10.GL_TRIANGLE_STRIP
                , cubeFacetsBuffer.remaining(),
                GL10.GL_UNSIGNED_BYTE, cubeFacetsBuffer);

这函数的意思是你传他画三个点的坐标组的位置（第一个从0开始，一个坐标组有三个float），比如这个cubeFacets就是说0、1、2三个坐标连起来画个三角形，然后0、2、3坐标画个三角形。

以下是完整代码

public class MainActivity extends Activity {
private GLSurfaceView mGLView;

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    mGLView = new GLSurfaceView(this); //这里使用的是自定义的GLSurfaceView的子类
    mGLView.setRenderer(new GLRenderer());
    setContentView(mGLView);
}

public void onPause(){
    super.onPause();
    mGLView.onPause();
}

public void onResume(){
    super.onResume();
    mGLView.onResume();
}

public class GLRenderer implements GLSurfaceView.Renderer {

    private float[] mTriangleArray={
            1.0f,1.0f,0.0f,
            1.0f,-1.0f,0.0f,
            -1.0f,-1.0f,0.0f,
            -1.0f,1.0f,0.0f
    };

    private float[] mColor ={
            1.0f,0.0f,0.0f,1.0f,
            1.0f,0.0f,0.0f,1.0f,
            1.0f,0.0f,0.0f,1.0f,
            1.0f,0.0f,0.0f,1.0f
    };
    private byte[] cubeFacets = new byte[]{
            0, 1, 2,
            0, 2, 3
    };
    private FloatBuffer mTriangleBuffer;
    private FloatBuffer mColorBuffer;
    ByteBuffer cubeFacetsBuffer;
    public GLRenderer() {

        mTriangleBuffer = floatBufferUtil(mTriangleArray);
        mColorBuffer = floatBufferUtil(mColor);
        cubeFacetsBuffer = ByteBuffer.wrap(cubeFacets);

    }

    @Override
    public void onDrawFrame(GL10 gl) {

        // 清除屏幕和深度缓存
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

        // 设置当前矩阵模式为模型视图。
        gl.glMatrixMode(GL10.GL_MODELVIEW);
        // 允许设置顶点
        //GL10.GL_VERTEX_ARRAY顶点数组
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        // 允许设置颜色
        //GL10.GL_COLOR_ARRAY颜色数组
        gl.glEnableClientState(GL10.GL_COLOR_ARRAY);

        // 重置当前的模型观察矩阵
        gl.glLoadIdentity();
        //将三角形在z轴上移动
        gl.glTranslatef(0f, 0.0f, -2.0f);

        // 设置三角形
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, mTriangleBuffer);
        // 设置三角形颜色
        gl.glColorPointer(4, GL10.GL_FLOAT, 0, mColorBuffer);
        // 绘制三角形
        gl.glDrawElements(GL10.GL_TRIANGLE_STRIP
                , cubeFacetsBuffer.remaining(),
                GL10.GL_UNSIGNED_BYTE, cubeFacetsBuffer);

        // 取消颜色设置
        gl.glDisableClientState(GL10.GL_COLOR_ARRAY);
        // 取消顶点设置
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);

        //绘制结束
        gl.glFinish();

    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        float ratio = (float) width / height;
        // 设置OpenGL场景的大小,(0,0)表示窗口内部视口的左下角，(w,h)指定了视口的大小
        gl.glViewport(0, 0, width, height);
        // 设置投影矩阵
        gl.glMatrixMode(GL10.GL_PROJECTION);
        // 重置投影矩阵
        gl.glLoadIdentity();
        // 设置视口的大小
        gl.glFrustumf(-ratio, ratio, -1, 1, 1, 10);
        //以下两句声明，以后所有的变换都是针对模型(即我们绘制的图形)
        gl.glMatrixMode(GL10.GL_MODELVIEW);
        gl.glLoadIdentity();

    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        // 设置白色为清屏
        gl.glClearColor(1, 1, 1, 1);

    }
}
// 定义一个工具方法，将float[]数组转换为OpenGL ES所需的FloatBuffer
private FloatBuffer floatBufferUtil(float[] arr)
{
    FloatBuffer mBuffer;
    // 初始化ByteBuffer，长度为arr数组的长度*4，因为一个int占4个字节
    ByteBuffer qbb = ByteBuffer.allocateDirect(arr.length * 4);
    // 数组排列用nativeOrder
    qbb.order(ByteOrder.nativeOrder());
    mBuffer = qbb.asFloatBuffer();
    mBuffer.put(arr);
    mBuffer.position(0);
    return mBuffer;
}

}