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POAndroid OpenGL ES 2, Drawing squares
 

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    <p><em><strong>EDIT: Problem solved!</em></strong> So I've been going through the official OpenGL ES 2 tutorials for Android, and I've gotten to the part that involves drawing shapes, but I can't seem to get a square to work. It draws a right triangle instead.</p> <p>I've included the code that I'm using to define and draw the shape, which is copied almost exactly from the tutorial. The Renderer class simply creates an instance of this shape and calls the draw method.</p> <p>For some reason, the tutorial does not give the values/declaration for vertexStride and vertexCount, so the ones I have in there are educated guesses. I've tried several values for vertexCount (1 thru 12), and none work.</p> <p>Thanks in advance.</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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    1. COActually, I found that just using GL_TRANGLE_FAN in place of GL_TRIANGLES as an argument for glDrawArrays() resolves the issue. Problem solved! Although if anybody could point me towards an API that actually explains all the methods and values instead of just listing them like Android's does, that'd be great.
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    2. COTake a look at this: http://stackoverflow.com/questions/6124636/gldrawarrays-vs-gldrawelements
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