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POOpenGL ES 2.0 Context in Android
 

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  1. POOpenGL ES 2.0 Context in Android
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    <p>I'm new to OpenGL on Android and I have read heavily documented samples, and I kinda understand it. But before trying to do anything complex, I want to draw a simple 2D white rectangle on a black bacground. Nothing else.</p> <p>I'm stuck at this error: <code>call to OpenGL ES API with no current context</code>, which seems to be that I'm calling something from the non-OpenGL <code>Thread</code>. The thing is that I'm not sure what is called from the OpenGL <code>Thread</code>. So here's my code</p> <p>//============== Activity ==================//</p> <pre><code>public class MainActivity extends Activity { public static String TAG = MainActivity.class.getSimpleName(); MyGLSurfaceView surface; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().setFlags( WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN ); surface = new MyGLSurfaceView(this); setContentView(surface); } @Override protected void onPause() { super.onPause(); surface.onPause(); } @Override protected void onResume() { super.onResume(); surface.onResume(); } } </code></pre> <p>//==================== GLSurfaceView ========================//</p> <pre><code>public class MyGLSurfaceView extends GLSurfaceView { MyGLSurfaceRenderer renderer; public MyGLSurfaceView(Context context) { super(context); setEGLContextClientVersion(2); renderer = new MyGLSurfaceRenderer(this); setRenderer(renderer); } } </code></pre> <p>//================== Renderer ==========================//</p> <pre><code>public class MyGLSurfaceRenderer implements GLSurfaceView.Renderer { Square square = new Square(); public MyGLSurfaceRenderer(MyGLSurfaceView surface) { } @Override public void onDrawFrame(GL10 gl) { GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT); square.draw(); } @Override public void onSurfaceChanged(GL10 gl, int width, int height) { // TODO Auto-generated method stub } @Override public void onSurfaceCreated(GL10 gl, EGLConfig config) { GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f); } } </code></pre> <p>//==================== Square ========================//</p> <pre><code>public class Square { private FloatBuffer vertexBuffer; private ShortBuffer drawListBuffer; // number of coordinates per vertex in this array static final int COORDS_PER_VERTEX = 3; static float squareCoords[] = { -0.5f, 0.5f, 0.0f, // top left -0.5f, -0.5f, 0.0f, // bottom left 0.5f, -0.5f, 0.0f, // bottom right 0.5f, 0.5f, 0.0f }; // top right private short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw vertices float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f }; 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;" + "}"; int mProgram; static final int vertexStride = COORDS_PER_VERTEX * 4; static final int vertexCount = 4; public Square() { // initialize vertex byte buffer for shape coordinates ByteBuffer bb = ByteBuffer.allocateDirect(squareCoords.length * 4); // (# of coordinate values * 4 bytes per float) bb.order(ByteOrder.nativeOrder()); vertexBuffer = bb.asFloatBuffer(); vertexBuffer.put(squareCoords); vertexBuffer.position(0); // initialize byte buffer for the draw list ByteBuffer dlb = ByteBuffer.allocateDirect(drawOrder.length * 2); // (# of coordinate values * 2 bytes per short) dlb.order(ByteOrder.nativeOrder()); drawListBuffer = dlb.asShortBuffer(); drawListBuffer.put(drawOrder); drawListBuffer.position(0); int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode); int fragmentShader = 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); // creates OpenGL ES program executables } 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 draw() { // Add program to OpenGL ES environment GLES20.glUseProgram(mProgram); // get handle to vertex shader's vPosition member int 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, vertexStride, 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, vertexCount); // Disable vertex array GLES20.glDisableVertexAttribArray(mPositionHandle); } } </code></pre>
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