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POHow to move opengl triangle in default android sample?
 

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  1. POHow to move opengl triangle in default android sample?
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    <p>I am using default android sample code <a href="http://developer.android.com/training/graphics/opengl/touch.html" rel="nofollow noreferrer">http://developer.android.com/training/graphics/opengl/touch.html</a> In this sample we can rotate triangle by toucht events.</p> <p>I want just to add movement by x,y axiss for test purposes. The point that triangle behaviour is not as i am expecting. What i am doing wrong?</p> <p>Code from tutorial with my new row hilighted:</p> <pre><code>public void onDrawFrame(GL10 unused) { // Draw background color GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT); // Set the camera position (View matrix) Matrix.setLookAtM(mVMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f); // Calculate the projection and view transformation Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mVMatrix, 0); // Draw square mSquare.draw(mMVPMatrix); **//Translating this matrix 'brakes' triangle -&gt; Matrix.translateM(mMVPMatrix, 0, 0, pos, -1.0f); //NOTHING happens here: ??? Why? -&gt; Matrix.translateM(mRotationMatrix, 0, pos, 0, -1.0f);** // Create a rotation for the triangle // long time = SystemClock.uptimeMillis() % 4000L; // float angle = 0.090f * ((int) time); Matrix.setRotateM(mRotationMatrix, 0, mAngle, 0, 0, -1.0f); // Combine the rotation matrix with the projection and camera view Matrix.multiplyMM(mMVPMatrix, 0, mRotationMatrix, 0, mMVPMatrix, 0); // Draw triangle mTriangle.draw(mMVPMatrix); } </code></pre> <p>Default behaviour:</p> <p><img src="https://i.stack.imgur.com/9t97X.png" alt="enter image description here"></p> <p>With my code:</p> <p><img src="https://i.stack.imgur.com/OrDvE.png" alt="enter image description here"></p>
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    1. USIevgen Naida
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    1. COHi. You should probably know that that tutorial is somewhat broken ([see this question](http://stackoverflow.com/questions/11925647/is-googles-android-opengl-tutorial-teaching-incorrect-linear-algebra)). One of the Google Engineers said they would fix it as soon as possible but it looks like from your example it has not yet been fixed. Their example code is a little bit nonsensical.
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    2. COAlso I think one of the answers there contains some fixed code, you may want to try that.
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    3. COYou can not do translation/rotation/scaling on MVP matrix and get results as you expect. you must translate/rotate your object in model matrix(or in View matrix for camera trans/rotation). Look at this http://stackoverflow.com/questions/5550620/the-purpose-of-model-view-projection-matrix to understand better what you need to do
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