Androidでgles20 circleを描画するときのランダムな線

Question

Android用OpenGLの学習を始めたばかりです。円を描くときに奇妙な問題が発生しています。頂点のいくつかは左と上の壁に張り付いていて、円から少しランダムに出ています。私はアプリを再起動するたびに、彼らは別の位置を持っています。円が描かれ

マイDrawScreenクラス：

public class DrawScreen implements GLSurfaceView.Renderer { 

Ball ball; 

public float mAngle; 

private int mProgram; 
private int maPositionHandle; 

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; \n" + 

     "attribute vec4 vPosition; \n" + 
     "void main(){    \n" + 

     // the matrix must be included as a modifier of gl_Position 
     " gl_Position = uMVPMatrix * vPosition; \n" + 

     "} \n"; 

private final String fragmentShaderCode = 
     "precision mediump float; \n" + 
       "void main(){    \n" + 
       " gl_FragColor = vec4 (0.63671875, 0.76953125, 0.22265625, 1.0); \n" + 
       "}       \n"; 

private int muMVPMatrixHandle; 
private float[] mMVPMatrix = new float[16]; 
private float[] mVMatrix = new float[16]; 
private float[] mProjMatrix = new float[16]; 


public void onSurfaceCreated(GL10 unused, EGLConfig config) { 

    ball = new Ball(); 

    // Set the background frame color 
    GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f); 

    muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix"); 
    Matrix.setLookAtM(mVMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f); 

    ball.initShapes(240, 360, 50); 

    int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode); 
    int fragmentShader = 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);     // creates OpenGL program executables 

    // get handle to the vertex shader's vPosition member 
    maPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition"); 

} 

public void onDrawFrame(GL10 unused) { 

    // Redraw background color 
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT); 

    // Add program to OpenGL environment 
    GLES20.glUseProgram(mProgram); 

    // Prepare the circle data 
    GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false, 0, ball.ballVB); 
    GLES20.glEnableVertexAttribArray(maPositionHandle); 

    // Apply a ModelView Projection transformation 
    Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mVMatrix, 0); 
    GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0); 

    // Draw the circle 
    GLES20.glDrawArrays(GLES20.GL_LINE_LOOP, 0, (int) (ball.getNumSeg() * 3)); 

} 

public void onSurfaceChanged(GL10 unused, int width, int height) { 
    GLES20.glViewport(0, 0, width, height); 

    float ratio = (float) width/height; 

    // this projection matrix is applied to object coodinates 
    // in the onDrawFrame() method 
    Matrix.frustumM(mProjMatrix, 0, -ratio, ratio, -1, 1, 3, 7); 

    muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix"); 
    Matrix.setLookAtM(mVMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f); 


} 

private 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; 

} 

}

そして、私のボールのクラスサークルが作成されます。

public class Ball { 

public FloatBuffer ballVB; 

private float cx, cy, r; 

float numSegments = 360; 

public void initShapes(float tx, float ty, float tr){ 

    cx = (tx/240.f) - 1.f; 
    cy = (ty/360.f) - 1.f; 
    r = (tr/240.f); 

    float ballCoords[] = new float[(int) (numSegments * 3)]; 

    double theta = (2 * 3.1415926/numSegments); 
    float c = (float) Math.cos(theta);//precalculate the sine and cosine 
    float s = (float) Math.sin(theta); 
    float t; 

    float x = r;//we start at angle = 0 
    float y = 0; 

    for(int i = 0; i < (numSegments * 3); i = i + 3) { 

     ballCoords[i] = (x + cx); 
     ballCoords[i + 1] = (y + cy); 
     ballCoords[i + 2] = (0); 

     //apply the rotation matrix 
     t = x; 
     x = c * x - s * y; 
     y = s * t + c * y; 

    } 

    // initialize vertex Buffer for triangle 
    ByteBuffer vbb = ByteBuffer.allocateDirect(
      // (# of coordinate values * 4 bytes per float) 
      ballCoords.length * 4); 
    vbb.order(ByteOrder.nativeOrder());// use the device hardware's native byte order 
    ballVB = vbb.asFloatBuffer(); // create a floating point buffer from the ByteBuffer 
    ballVB.put(ballCoords); // add the coordinates to the FloatBuffer 
    ballVB.position(0);   // set the buffer to read the first coordinate 

} 

public float getNumSeg(){ 

    return numSegments; 

} 

}私がきた

何時間もインターネットを掃除していたが、何も見つけられなかった。あなたたちが私を助けてくれることを願っています。

Answer 1

GLES20.glDrawArrays(GLES20.GL_LINE_LOOP, 0, (int) (ball.getNumSeg() * 3));

私はこれの不審なんだが、個々の頂点を参照セグメントですか？

glDrawArraysの最後の引数は、浮動小数点数ではなく、頂点の数です。おそらく、* 3の乗数をglDrawArraysから削除する必要があります。

余分な線は、実際に割り当てた頂点の3倍の図を描画している可能性があります。