android - GLES20.glGetAttribLocation() は -1 を返します

Question

Android OpenGL ES 2.0 アプリケーションの動作に問題があります。いくつかのチュートリアルに非常によく似た「Triangle」クラスがあります。「draw」関数では、mPositionHande は次のコード行の後に -1 です。

mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");

以下は、シェーダー コードなどを含む三角形クラス全体です。これを引き起こす可能性のあるアイデアはありますか? 申し訳ありませんが、私は OpenGL プログラミングが初めてなので、これはばかげた質問かもしれません。

public class Triangle {

private final String vertexShaderCode =
    // This matrix member variable provides a hook to manipulate
    // the coordinates of the objects that use this vertex shader
    "uniform mat4 uMVPMatrix;" +

    "attribute vec4 vPosition;" +
    "void main() {" +
    // the matrix must be included as a modifier of gl_Position
    "  gl_Position = uMVPMatrix * vPosition;" +
    "}";

private final String fragmentShaderCode =
    "precision mediump float;" +
    "uniform vec4 vColor;" +
    "void main() {" +
    "  gl_FragColor = vColor;" +
    "}";

private final FloatBuffer vertexBuffer;
private final int mProgram;
private int mPositionHandle;
private int mColorHandle;
private int mMVPMatrixHandle;

// number of coordinates per vertex in this array
static final int COORDS_PER_VERTEX = 3;
public float triangleCoords[];

private final int vertexCount = 3; //triangleCoords.length / COORDS_PER_VERTEX;
private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex

// Set color with red, green, blue and alpha (opacity) values
float color[] = { 0.5f, 1.0f, 0.5f, 1.0f };
float edgeColor[] = { 0.0f, 0.0f, 0.0f, 1.0f };

public Triangle(float[] vertices) {
    this.triangleCoords = vertices;

    // initialize vertex byte buffer for shape coordinates
    ByteBuffer bb = ByteBuffer.allocateDirect(
            // (number of coordinate values * 4 bytes per float)
            triangleCoords.length * 4);
    // use the device hardware's native byte order
    bb.order(ByteOrder.nativeOrder());

    // create a floating point buffer from the ByteBuffer
    vertexBuffer = bb.asFloatBuffer();
    // add the coordinates to the FloatBuffer
    vertexBuffer.put(triangleCoords);
    // set the buffer to read the first coordinate
    vertexBuffer.position(0);

    // prepare shaders and OpenGL program
    int vertexShader = MyRenderer.loadShader(GLES20.GL_VERTEX_SHADER,
                                               vertexShaderCode);
    int fragmentShader = MyRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER,
                                                 fragmentShaderCode);

    mProgram = GLES20.glCreateProgram();             // create empty OpenGL Program
    GLES20.glAttachShader(mProgram, vertexShader);   // add the vertex shader to program
    GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
    GLES20.glLinkProgram(mProgram);                  // create OpenGL program executables

}

public void draw(float[] mvpMatrix) {
    // 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 facet 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 facet
    GLES20.glUniform4fv(mColorHandle, 1, color, 0);

    // get handle to shape's transformation matrix
    mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
    MyRenderer.checkGlError("glGetUniformLocation");

    // Apply the projection and view transformation
    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);
    MyRenderer.checkGlError("glUniformMatrix4fv");

    // Draw the facet
    GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);
    //If edge mode
    //GLES20.glUniform4fv(mColorHandle, 1, edgeColor, 0);
    //GLES20.glLineWidth(2.0f);
    //GLES20.glDrawArrays(GLES20.GL_LINE_STRIP, 0, vertexCount);

    // Disable vertex array
    GLES20.glDisableVertexAttribArray(mPositionHandle);
}

}