Question

I am trying to build a little Open GL2.0 demo application on android but i am getting the following errors

in log cat

07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context     (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context         (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context     (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context (logged once per thread)
07-02 20:50:40.110: E/libEGL(1252): call to OpenGL ES API with no current context (logged once per thread)

in the Console

[2012-07-02 20:50:44 - Emulator]     development/tools/emulator/opengl/host/libs/Translator/GLES_V2/GLESv2Imp.cpp:glGetAttribLoc    ation:826 error 0x501
[2012-07-02 20:50:44 - Emulator]     development/tools/emulator/opengl/host/libs/Translator/GLES_V2/GLESv2Imp.cpp:glGetUniformLocation:1383 error 0x501

my code

View

package limitliss.graphics.play;


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.content.Context;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.GLSurfaceView.Renderer;
import android.opengl.GLU;

public class OGLView extends GLSurfaceView implements Renderer {

private int mColorType = 0;

private float rotx = 0.0f;
private float roty = 0.0f;    
Triangle tri = new Triangle();

public OGLView(Context context) {
    super(context);
    setEGLContextClientVersion(2);

    this.setRenderer(this); 
    setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
    // TODO Auto-generated constructor stub
}



public static int loadShader(int type, String shaderCode){

    // create a vertex shader type (GLES20.GL_VERTEX_SHADER)
    // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER)
    int shader = GLES20.glCreateShader(type);

    // add the source code to the shader and compile it
    GLES20.glShaderSource(shader, shaderCode);
    GLES20.glCompileShader(shader);

    return shader;
}





public void onSurfaceCreated(GL10 unused, EGLConfig config) {
    // Set the background frame color
    GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
    tri.draw();
}

public void onDrawFrame(GL10 unused) {
    // Redraw background color
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
    tri.draw();
}

public void onSurfaceChanged(GL10 unused, int width, int height) {
    GLES20.glViewport(0, 0, width, height);
}
}


Triangle

package limitliss.graphics.play;

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

import javax.microedition.khronos.opengles.GL10;

import android.opengl.GLES20;



public class Triangle {

float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f };

private FloatBuffer vertexBuffer;
int mProgram;
int mPositionHandle;
private final String vertexShaderCode =
        "attribute vec4 vPosition;" +
        "void main() {" +
        "  gl_Position = vPosition;" +
        "}";

    private final String fragmentShaderCode =
        "precision mediump float;" +
        "uniform vec4 vColor;" +
        "void main() {" +
        "  gl_FragColor = vColor;" +
        "}";
// number of coordinates per vertex in this array
static final int COORDS_PER_VERTEX = 3;
static float triangleCoords[] = { // in counterclockwise order:
     0.0f,  0.622008459f, 0.0f,   // top
    -0.5f, -0.311004243f, 0.0f,   // bottom left
     0.5f, -0.311004243f, 0.0f};   // bottom right

public Triangle() {
    // initialize vertex byte buffer for shape coordinates
    ByteBuffer bb = ByteBuffer.allocateDirect(
            // (number of coordinate values * 4 bytes per float)
            triangleCoords.length * 4);
    // use the device hardware's native byte order
    bb.order(ByteOrder.nativeOrder());

    // create a floating point buffer from the ByteBuffer
    vertexBuffer = bb.asFloatBuffer();
    // add the coordinates to the FloatBuffer
    vertexBuffer.put(triangleCoords);
    // set the buffer to read the first coordinate
    vertexBuffer.position(0);

    int vertexShader =  OGLView.loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
    int fragmentShader =  OGLView.loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);

    mProgram = GLES20.glCreateProgram();             // create empty OpenGL ES Program
    GLES20.glAttachShader(mProgram, vertexShader);   // add the vertex shader to program
    GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
    GLES20.glLinkProgram(mProgram);    
}

public void draw() {

    // Add program to OpenGL ES environment
    GLES20.glUseProgram(mProgram);

    // get handle to vertex shader's vPosition member
    mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");

    // Enable a handle to the triangle vertices
    GLES20.glEnableVertexAttribArray(mPositionHandle);

    // Prepare the triangle coordinate data
    GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX,
                                 GLES20.GL_FLOAT, false,
                                 COORDS_PER_VERTEX, vertexBuffer);

    // get handle to fragment shader's vColor member
    int mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");

    // Set color for drawing the triangle
    GLES20.glUniform4fv(mColorHandle, 1, color, 0);

    // Draw the triangle
    GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 3);

    // Disable vertex array
    GLES20.glDisableVertexAttribArray(mPositionHandle);
}

public void render(GL10 gl){

    gl.glPushMatrix();
    gl.glColor4f(this.color[0],this.color[1],this.color[2],this.color[3]); 
    gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glDrawArrays(GL10.GL_TRIANGLE_FAN, 0, 3);
    gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glPopMatrix();
}
}

Answer 1

You’re getting call to OpenGL ES API with no current context errors because you’re creating your triangle Triangle tri = new Triangle(); outside of the OpenGL thread (and the triangle constructor is making opengl calls). Only the code inside the OpenGL callbacks (onSurfaceCreated, onDrawFrame, etc) are executed on the opengl thread.

Put tri = new Triangle() inside of onSurfaceCreated and those errors should go away.