Android UI How to - Draw a Triangle using OpenGL

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The following code shows how to Draw a Triangle using OpenGL.

Example

Main Activity Java code

package com.java2s.myapplication4.app;
/*from  ww w .  j a  v  a 2 s.c  o m*/
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import android.app.Activity;
import android.opengl.GLSurfaceView;
import android.opengl.GLSurfaceView.Renderer;
import android.os.Bundle;
import android.util.Log;
import android.view.Window;
import android.view.WindowManager;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

class Triangle {

    private FloatBuffer vertexBuffer;
    private float vertices[] = {
            100.0f, 150.0f, 0.0f, // V1 - first vertex (x,y,z)
            219.0f, 150.0f, 0.0f, // V2 - second vertex
            160.0f, 279.0f, 0.0f // V3 - third vertex
    };

    public Triangle() {
        ByteBuffer byteBuffer = ByteBuffer.allocateDirect(3 * 3 * 4);
        byteBuffer.order(ByteOrder.nativeOrder());
        vertexBuffer = byteBuffer.asFloatBuffer();
        vertexBuffer.put(vertices);
        vertexBuffer.flip();
    }

    public void draw(GL10 gl) {
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glColor4f(0.0f, 1.0f, 0.0f, 0.5f);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);
        gl.glDrawArrays(GL10.GL_TRIANGLES, 0, vertices.length / 3);
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    }
}

public class MainActivity extends Activity {

    private GLSurfaceView glView;
    private Triangle triangle;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        glView = new GLSurfaceView(this);
        glView.setRenderer(new MyOpenGLRenderer());
        setContentView(glView);
    }

    class MyOpenGLRenderer implements Renderer {
        @Override
        public void onSurfaceChanged(GL10 gl, int width, int height) {
            Log.d("MyOpenGLRenderer", "Surface changed. Width=" + width + " Height=" + height);
            gl.glViewport(0, 0, width, height);
            gl.glMatrixMode(GL10.GL_PROJECTION);
            gl.glLoadIdentity();
            gl.glOrthof(0, 320, 0, 480, 1, -1);
        }

        @Override
        public void onSurfaceCreated(GL10 gl, EGLConfig config) {
            Log.d("MyOpenGLRenderer", "Surface created");
            triangle = new Triangle();
        }

        @Override
        public void onDrawFrame(GL10 gl) {
            gl.glClearColor(0.0f, 0.5f, 0.0f, 1f);
            gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
            triangle.draw(gl);
        }
    }
}

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