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    Draw trinagle in android openGL 2.0


    I am trying to create a triangle in openGL 2.0 but some some reason background is shows up but no triangle. I am following this tutorial: http://developer.android.com/training/graphics/opengl/environment.html
    i have the same code as on tutorial but for some reason the triangle is not showing up.
    may be i missed some thing or i am doing some thing wrong?

    i have two class.
    GlRender.java
    GLTriangle.java

    i think the problem is in GLTriangle draw method.

    Code:
    public class GlRender implements Renderer {
    
    	private GLTriangle glTriangleObj;
    
    	private final float[] mModelMatrix = new float[16];
    	private final float[] mProjectionMatrix = new float[16];
    	private final float[] mViewMatrix = new float[16];
    	private final float[] mRotationMatrix = new float[16];
    
    	/************************/
    	/*** create() method ***/
    	/************************/
    	@Override
    	public void onSurfaceCreated(GL10 gl, EGLConfig config) {
    		// Set the background color
    		// 0 to 1
    		// 1 = no transparent
    		GLES20.glClearColor(0.8f, 0.2f, 0.2f, 1f);
    		gl.glClearDepthf(1f);
    
    		glTriangleObj = new GLTriangle();
    		// glSquare = new Square(); //etc...
    
    		// postion the eye behind the origin
    		final float eyeX = 0.0f;
    		final float eyeY = 0.0f;
    		final float eyeZ = 1.5f;
    
    		// we are looking toward the distance
    		final float lookX = 0.0f;
    		final float lookY = 0.0f;
    		final float lookZ = -5.0f;
    
    		// Set our up vector. This is where our head would be pointing were we
    		// holding the camera.
    		final float upX = 0.0f;
    		final float upY = 1.0f;
    		final 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, lookX, lookY,
    				lookZ, upX, upY, upZ);
    	}
    
    	/********************/
    	/*** paint method ***/
    	/********************/
    	@Override
    	public void onDrawFrame(GL10 gl) {
    		// Redraw background color
    		GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);
    
    		// do a complete rotation every 10 seconds
    		// long time = SystemClock.uptimeMillis() % 10000L;
    		// float angleInDegree = (360.0f / 10000.0f) * ((int) time);
    		// draw the triangle face straight on
    		// Matrix.setIdentityM(mModelMatrix, 0);
    		// Matrix.rotateM(mModelMatrix, 0, angleInDegree, 0.0f, 0.0f, 1.0f);
    
    		// Set the camera position (View matrix)
    		Matrix.setLookAtM(mViewMatrix, 0, 0, -2, 0, 0f, 0f, 0f, 0f, 2.0f, 0.0f);
    
    		// Calculate the projection and view transformation
    		Matrix.multiplyMM(mModelMatrix, 0, mProjectionMatrix, 0, mViewMatrix, 0);
    
    		glTriangleObj.draw(mModelMatrix);
    	}
    
    	/*****************************/
    	/*** landscape to portrait ***/
    	/*****************************/
    	@Override
    	public void onSurfaceChanged(GL10 gl, int width, int height) {
    		if (height == 0)
    			height = 1;
    
    		// Set the OpenGL viewport to the same size as the surface.
    		GLES20.glViewport(0, 0, width, height);
    
    		// 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 = 25.0f;
    
    		Matrix.frustumM(mProjectionMatrix, 0, left, right, bottom, top, near,
    				far);
    	}
    }


    GLTriangle.java

    Code:
    public class GLTriangle {
    	// always same
    	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;" + "}";
    
    	// always start at zero when ploting a point as defult
    	// trinagle Coordinates - vertex = 3(x y z)
    	private float trinagleCoords[] = { 0f, 1f, // V 0 - top
    			1f, -1, // V 1 - right bottom
    			-1f, 1f // V 2 - left bottom
    	};
    	private int COORDS_PER_VERTEX = 2; // number of points
    	private FloatBuffer vertexBuffer;
    
    	private short[] drawOrder = { 0, 1, 2 }; // order
    	private ShortBuffer orderBuffer;
    
    	float color[] = { 0.5f, 1f, 0f, 1f };
    
    	private int vertexCount = trinagleCoords.length / COORDS_PER_VERTEX;
    	private int vertexStride = COORDS_PER_VERTEX * 4; // bytes per vertex
    
    	// used to pass in the transformation matrix
    	private final int mProgram;
    	// used to pass in model poition information
    	private int mPositionHandle;
    	// used to pass inmodel color information
    	private int mColorHandle;
    	
    	private int mMVPMatrixHandle;
    	
    	public GLTriangle() {
    		// vertices - has to be 4
    		ByteBuffer byteBuffer = ByteBuffer
    				.allocateDirect(trinagleCoords.length * 4);
    		byteBuffer.order(ByteOrder.nativeOrder());
    		vertexBuffer = byteBuffer.asFloatBuffer();
    		vertexBuffer.put(trinagleCoords);
    		vertexBuffer.position(0);
    
    		// draw order - has to be 2
    		ByteBuffer pointByteBuffer = ByteBuffer
    				.allocateDirect(drawOrder.length * 2);
    		pointByteBuffer.order(ByteOrder.nativeOrder());
    		orderBuffer = pointByteBuffer.asShortBuffer();
    		orderBuffer.put(drawOrder);
    		orderBuffer.position(0);
    
    		// shader - always same
    		int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
    		int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER,
    				fragmentShaderCode);
    		// create empty OpenGL ES Program
    		mProgram = GLES20.glCreateProgram();
    		// add the vertex shader to program
    		GLES20.glAttachShader(mProgram, vertexShader);
    		// add the fragment shader to program
    		GLES20.glAttachShader(mProgram, fragmentShader);
    		// creates OpenGL ES program executables
    		GLES20.glLinkProgram(mProgram);
    	}
    
    	/************/
    	/*** same ***/
    	/************/
    	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(float[] mModelMatrix) {
    		// Add program to OpenGL 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, vertexStride, vertexBuffer);
    
    		// get handle to fragment shader's vColor member
    		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);
    
    		// get handle to shape's transformation matrix
    		mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
    
    		// Apply the projection and view transformation
    		GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mModelMatrix, 0);
    
    		// Draw the triangle
    		GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);
    	
    	}
    }
    Last edited by game2d; September 2nd, 2013 at 08:25 PM.

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