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PODrawing 3D polygon using vertex array
 

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  1. PODrawing 3D polygon using vertex array
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    <p>I have a short program which draw a 3D <code>GL.GL_QUADS</code> , here its <code>display()</code> method - </p> <pre><code>public void display(GLAutoDrawable drawable) { .... gl.glBegin(GL.GL_QUADS); // of the color cube // Top-face gl.glColor3f(0.0f, 1.0f, 0.0f); // green gl.glVertex3f(1.0f, 1.0f, -1.0f); gl.glVertex3f(-1.0f, 1.0f, -1.0f); gl.glVertex3f(-1.0f, 1.0f, 1.0f); gl.glVertex3f(1.0f, 1.0f, 1.0f); // Bottom-face gl.glColor3f(1.0f, 0.5f, 0.0f); // orange gl.glVertex3f(1.0f, -1.0f, 1.0f); gl.glVertex3f(-1.0f, -1.0f, 1.0f); gl.glVertex3f(-1.0f, -1.0f, -1.0f); gl.glVertex3f(1.0f, -1.0f, -1.0f); // Front-face gl.glColor3f(1.0f, 0.0f, 0.0f); // red gl.glVertex3f(1.0f, 1.0f, 1.0f); gl.glVertex3f(-1.0f, 1.0f, 1.0f); gl.glVertex3f(-1.0f, -1.0f, 1.0f); gl.glVertex3f(1.0f, -1.0f, 1.0f); // Back-face gl.glColor3f(1.0f, 1.0f, 0.0f); // yellow gl.glVertex3f(1.0f, -1.0f, -1.0f); gl.glVertex3f(-1.0f, -1.0f, -1.0f); gl.glVertex3f(-1.0f, 1.0f, -1.0f); gl.glVertex3f(1.0f, 1.0f, -1.0f); // Left-face gl.glColor3f(0.0f, 0.0f, 1.0f); // blue gl.glVertex3f(-1.0f, 1.0f, 1.0f); gl.glVertex3f(-1.0f, 1.0f, -1.0f); gl.glVertex3f(-1.0f, -1.0f, -1.0f); gl.glVertex3f(-1.0f, -1.0f, 1.0f); // Right-face gl.glColor3f(1.0f, 0.0f, 1.0f); // violet gl.glVertex3f(1.0f, 1.0f, -1.0f); gl.glVertex3f(1.0f, 1.0f, 1.0f); gl.glVertex3f(1.0f, -1.0f, 1.0f); gl.glVertex3f(1.0f, -1.0f, -1.0f); .... } </code></pre> <p>Now I want to change the above drawing to "Vertex Arrays" mode and to get same results , so I did the following :</p> <ol> <li>Created a <code>float</code> array of all the vertices coodinates of the <code>GL.GL_QUADS</code> .</li> <li><code>put</code> this array to a <code>Buffer</code> . </li> <li>Tell OpenGL where the vertices are (8 vertices) . </li> <li>Tell OpenGL which indices to draw . </li> </ol> <p>Here is the main code I wrote (<strong>edited</strong>) -</p> <pre><code>public class DisplayWithArray extends GLCanvas implements GLEventListener, KeyListener { private float[] cubeVertices = { 1.0f, 1.0f, -1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, -1.0f, -1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, -1.0f, 1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f, -1.0f }; private float[] colorVertices ={ 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.5f, 0.0f, 1.0f, 0.5f, 0.0f, 1.0f, 0.5f, 0.0f, 1.0f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f }; // 1st edit - 24 positions of the GL.GL_QUADS private int[] indices = new int[24] ; private IntBuffer indicesBuf ; } public DisplayWithArray(GLCapabilities capabilities, int width, int height) { for (int i=0 ; i&lt;24 ; i++) { this.indices[i] = i ; } public void init(GLAutoDrawable drawable) { ... final GL gl = drawable.getGL(); ... setupPointer(gl); } public void display(GLAutoDrawable drawable) { final GL gl = drawable.getGL(); // draw gl.glDrawArrays(GL.GL_QUADS, 0, 24); } public void setupPointer(GL gl) { FloatBuffer tmpVerticesBuf = BufferUtil .newFloatBuffer(cubeVertices.length); ; FloatBuffer tmpColorVerticesBuf = BufferUtil .newFloatBuffer(colorVertices.length); for (int i = 0; i &lt; cubeVertices.length; i++) { tmpVerticesBuf.put(cubeVertices[i]); } for (int i = 0; i &lt; colorVertices.length; i++) { tmpColorVerticesBuf.put(colorVertices[i]); } tmpVerticesBuf.rewind(); tmpColorVerticesBuf.rewind(); gl.glEnableClientState(GL.GL_VERTEX_ARRAY); gl.glVertexPointer(3, GL.GL_FLOAT, 0, tmpVerticesBuf); gl.glColorPointer(3, GL.GL_FLOAT, 0, tmpColorVerticesBuf); // Indices of polygon IntBuffer tmpIndicesBuf = BufferUtil.newIntBuffer(this.indices.length); for (int i = 0; i &lt; indices.length; i++) { tmpIndicesBuf.put(indices[i]); } tmpIndicesBuf.rewind(); indicesBuf = tmpIndicesBuf ; } </code></pre> <p>When I run it I get an exception <code>Exception in thread "AWT-EventQueue-0" javax.media.opengl.GLException: glGetError() returned the following error codes after a call to glDrawElements(): GL_INVALID_ENUM at DisplayWithArray.display(DisplayWithArray.java:152)</code></p> <p>point to the line - <code>gl.glDrawElements(GL.GL_QUADS, indices.length, GL.GL_INT, indicesBuf); </code></p> <p>What is wrong here ? </p> <p><strong>Edit:</strong></p> <p>I changed the <code>indices</code> array to range [0,5] - according to 6 face of the <code>GL.GL_QUADS</code>. And extend <code>tmpColorVerticesBuf</code> array to 72 indices (4 times each color) .</p> <p>Still I have same exception as mentioned above . </p> <p><strong>Edit 2:</strong> (now it works well) Solve by comparing between <code>cubeVertices</code> and <code>colorVertices</code> sizes (72 each array) , and in <code>display()</code> use <code>gl.glDrawArrays(GL.GL_QUADS, 0, 24)</code> (24 elements of size 3)</p>
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