Question

I’m new to OpenGL and Android and my code is not working and I don’t know why. I don’t know how to debug the code with Netbeans and AVD (android 4.0.3), so I ask for your help.

package com.egg.game.test;

import android.opengl.GLES20;
import java.nio.FloatBuffer;

public class glTriangle {

private int mProgram;
private int mPositionHandle;
private int mColorHandle;
private static int COORDS_PER_VERTEX = 3;
private int vertexStride = Float.SIZE * COORDS_PER_VERTEX;
private int vertexCount;
private FloatBuffer vertexBuffer;
private float[] color;
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;"
        + "}";

public glTriangle() {

    color = new float[]{.5f, .2f, 0f, 1.0f};

    vertexCount = 3;

    vertexBuffer = FloatBuffer.allocate(Float.SIZE * COORDS_PER_VERTEX * vertexCount);
    float[] buffer = vertexBuffer.array();
    buffer[0] = 0f;
    buffer[1] = 0f;
    buffer[2] = 0f;
    buffer[3] = 1f;
    buffer[4] = 0f;
    buffer[5] = 0f;
    buffer[6] = 0f;
    buffer[7] = 1f;
    buffer[8] = 0f;


    int vertexShader = GameRederer.loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
    int fragmentShader = GameRederer.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 void draw() {
    // Add program to OpenGL ES 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);

    GLES20.glEnableVertexAttribArray(mPositionHandle);


    // 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);
}

I Changed the buffer code to this:

    vertexBuffer = ByteBuffer.allocateDirect(Float.SIZE * COORDS_PER_VERTEX * vertexCount).order(ByteOrder.nativeOrder()).asFloatBuffer();
    vertexBuffer.put(0f);
    vertexBuffer.put(0f);
    vertexBuffer.put(0f);
    vertexBuffer.put(10f);
    vertexBuffer.put(0f);
    vertexBuffer.put(0f);
    vertexBuffer.put(0f);
    vertexBuffer.put(10f);
    vertexBuffer.put(0f);
    vertexBuffer.position(0);

Now i don’t get any error but!!!! my triangle didn’t get draw!

Answer 1

You allocate floats in your FloatBuffer and convert them to a array.
Then you populate your array, but not your FloatBuffer, maybe this is the error.

float[] buffer = new float[] {
...
};
vertexBuffer.put(buffer);
vertexBuffer.position(0);

I’m not sure, maybe .array() returns a changeable reference, maybe it clones the data.
Just try it!