Point is not showing in opengles 2.0

Question

I am trying to learn OpenGLES 2.0 in android in depth. I am trying to draw a Simple Point at the center of screen but somehow , the point is not showing .

Answer 1

Here is a class I built based around your code for displaying the point. Since you will probably use more than one point eventually it is better to push the points into a vertex array as shown.

    package point.example.point;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.Matrix;

public class PointRenderer implements GLSurfaceView.Renderer 
{
    private float[] mModelMatrix = new float[16];
    private float[] mViewMatrix = new float[16];
    private float[] mProjectionMatrix = new float[16];
    private float[] mMVPMatrix = new float[16];
    private int mMVPMatrixHandle;
    private int mPositionHandle;

    float[] vertices = {
              0.0f,0.0f,0.0f
            };
    FloatBuffer vertexBuf;  

    @Override
    public void onSurfaceCreated(GL10 glUnused, EGLConfig config) 
    {       
        vertexBuf = ByteBuffer.allocateDirect(vertices.length * 4).order(ByteOrder.nativeOrder()).asFloatBuffer();
        vertexBuf.put(vertices).position(0);        

        // Set the background clear color to gray.
        GLES20.glClearColor(0.5f, 0.5f, 0.5f, 0.5f);

        float eyeX=0.0f;
        float eyeY=0.0f;
        float eyeZ=0.0f;

        float centerX=0.0f;
        float centerY=0.0f;
        float centerZ=-5.0f;

        float upX=0.0f;
        float upY=1.0f;
        float upZ=0.0f;

        // Set the view matrix. This matrix can be said to represent the camera position.
        // NOTE: In OpenGL 1, a ModelView matrix is used, which is a combination of a model and
        // view matrix. In OpenGL 2, we can keep track of these matrices separately if we choose.
        Matrix.setLookAtM(mViewMatrix, 0, eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ);

        final String vertexShader =
                            "uniform mat4 u_MVPMatrix;      \n"       
                          + "attribute vec4 a_Position;     \n"     
                          + "void main()                    \n"
                          + "{                              \n"
                          + "   gl_Position = u_MVPMatrix   \n"
                          + "               * a_Position;   \n"
                          + "   gl_PointSize = 10.0;       \n"
                          + "}                              \n";

        final String fragmentShader =
                            "precision mediump float;       \n"                           
                          + "void main()                    \n"
                          + "{                              \n"
                          + "   gl_FragColor = vec4(1.0,    \n" 
                          + "   1.0, 1.0, 1.0);             \n"
                          + "}                              \n";    

        // Load in the vertex shader.
        int vertexShaderHandle = GLES20.glCreateShader(GLES20.GL_VERTEX_SHADER);

        if (vertexShaderHandle != 0) 
        {
            // Pass in the shader source.
            GLES20.glShaderSource(vertexShaderHandle, vertexShader);

            // Compile the shader.
            GLES20.glCompileShader(vertexShaderHandle);

            // Get the compilation status.
            final int[] compileStatus = new int[1];
            GLES20.glGetShaderiv(vertexShaderHandle, GLES20.GL_COMPILE_STATUS, compileStatus, 0);

            // If the compilation failed, delete the shader.
            if (compileStatus[0] == 0) 
            {               
                GLES20.glDeleteShader(vertexShaderHandle);
                vertexShaderHandle = 0;
            }
        }

        if (vertexShaderHandle == 0)
        {
            throw new RuntimeException("Error creating vertex shader.");
        }

        // Load in the fragment shader shader.
        int fragmentShaderHandle = GLES20.glCreateShader(GLES20.GL_FRAGMENT_SHADER);

        if (fragmentShaderHandle != 0) 
        {
            // Pass in the shader source.
            GLES20.glShaderSource(fragmentShaderHandle, fragmentShader);

            // Compile the shader.
            GLES20.glCompileShader(fragmentShaderHandle);

            // Get the compilation status.
            final int[] compileStatus = new int[1];
            GLES20.glGetShaderiv(fragmentShaderHandle, GLES20.GL_COMPILE_STATUS, compileStatus, 0);

            // If the compilation failed, delete the shader.
            if (compileStatus[0] == 0) 
            {               
                GLES20.glDeleteShader(fragmentShaderHandle);
                fragmentShaderHandle = 0;
            }
        }

        if (fragmentShaderHandle == 0)
        {
            throw new RuntimeException("Error creating fragment shader.");
        }

        // Create a program object and store the handle to it.
        int programHandle = GLES20.glCreateProgram();

        if (programHandle != 0) 
        {
            // Bind the vertex shader to the program.
            GLES20.glAttachShader(programHandle, vertexShaderHandle);           
            // Bind the fragment shader to the program.
            GLES20.glAttachShader(programHandle, fragmentShaderHandle);
            // Bind attributes
            GLES20.glBindAttribLocation(programHandle, 0, "a_Position");
            // Link the two shaders together into a program.
            GLES20.glLinkProgram(programHandle);
            // Get the link status.
            final int[] linkStatus = new int[1];
            GLES20.glGetProgramiv(programHandle, GLES20.GL_LINK_STATUS, linkStatus, 0);
            // If the link failed, delete the program.
            if (linkStatus[0] == 0) 
            {               
                GLES20.glDeleteProgram(programHandle);
                programHandle = 0;
            }
        }

        if (programHandle == 0)
        {
            throw new RuntimeException("Error creating program.");
        }

        // Set program handles. These will later be used to pass in values to the program.
        mMVPMatrixHandle = GLES20.glGetUniformLocation(programHandle, "u_MVPMatrix");        
        mPositionHandle = GLES20.glGetAttribLocation(programHandle, "a_Position");

        // Tell OpenGL to use this program when rendering.
        GLES20.glUseProgram(programHandle);        
    }   

    @Override
    public void onSurfaceChanged(GL10 glUnused, int width, int height) 
    {
        // Set the OpenGL viewport to the same size as the surface.
        GLES20.glViewport(0, 0, width, height);

        // Create a new perspective projection matrix. The height will stay the same
        // while the width will vary as per aspect ratio.
        final float ratio = (float) width / height;
        final float left = -ratio;
        final float right = ratio;
        final float bottom = -1.0f;
        final float top = 1.0f;
        final float near = 1.0f;
        final float far = 100.0f;

        Matrix.frustumM(mProjectionMatrix, 0, left, right, bottom, top, near, far);
    }   

    @Override
    public void onDrawFrame(GL10 glUnused) 
    {
        GLES20.glClear(GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);                    

        Matrix.setIdentityM(mModelMatrix, 0);
        //Push to the distance - note this will have no effect on a point size
        Matrix.translateM(mModelMatrix, 0, 0.0f, 0.0f, -5.0f);
        Matrix.multiplyMV(mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0);
        Matrix.multiplyMV(mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0);
        GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0);

        //Send the vertex
        GLES20.glVertexAttribPointer(mPositionHandle, 3, GLES20.GL_FLOAT, false, 0, vertexBuf);
        GLES20.glEnableVertexAttribArray(mPositionHandle);

        //Draw the point
        GLES20.glDrawArrays(GLES20.GL_POINTS, 0, 1);        

    }   
}