我刚刚开始学习适用于 Android 的 OpenGL，并且在绘制圆圈时遇到了一个奇怪的问题。它的一些顶点粘在左边，顶墙使线条随机地从圆圈中伸出。每次我重新启动应用程序时，他们都有不同的位置。
绘制圆圈的我的 DrawScreen 类：
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;
}
}
还有我创建圆圈的 Ball 类：
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;
}
}
我已经在互联网上搜索了几个小时，但没有找到任何东西。希望你们能帮助我。