我刚开始学习 Android 版 OpenGL，在画线时遇到了一个奇怪的问题。我想要做的就是根据手指运动画一条线。现在，一旦我开始滑动，我总是会得到一条从原点 (0,0) 开始跟随我的运动的线。
这里是一张图片:
http://imageshack.us/photo/my-images/137/screenshot2012061312174.jpg/
箭头表示我的手指运动，从原点(红色圆圈)开始的线是我整个运动之后提到的线。
不要为 Coords 数组而烦恼 我知道这不是最佳实践，但我调试了整个程序并且找不到涉及此数组的任何错误。
我可能应该提到 ArrayList 点包含我生成的所有点。
我想暂时解决这个问题，但我真的无法理解任何可能有帮助的建议
这是我的整个渲染类。
公共(public)类 HelloOpenGLES20Renderer 实现 GLSurfaceView.Renderer {
private FloatBuffer triangleVB;
private int mProgram;
private int maPositionHandle;
public ArrayList<PointWrapper> points;
private int muMVPMatrixHandle;
private float[] mMVPMatrix = new float[16];
private float[] mMMatrix = new float[16];
private float[] mVMatrix = new float[16];
private float[] mProjMatrix = new float[16];
private int[] viewport = new int[4];
private ArrayList<Float> coordinates;
float[] Coords = new float[100000];
boolean first;
private int counter;
private PointWrapper last;
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 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 HelloOpenGLES20Renderer() {
points = new ArrayList<PointWrapper>();
first = true;
this.counter = 0;
last = new PointWrapper();
coordinates = new ArrayList<Float>();
}
private float[] convertCoordinates(PointWrapper f) {
float[] vector = new float[4];
GLU.gluUnProject(f.point.x, f.point.y, 0.0f, mVMatrix, 0, mProjMatrix,
0, viewport, 0, vector, 0);
return vector;
}
private void initShapes() {
ArrayList<PointWrapper> points2 = new ArrayList<PointWrapper>(points);
float[] vector;
if (!points2.isEmpty()) {
if(points2.size()%2==1){
points2.remove(points2.size()-1);
}
for (int i = counter/2; i < points2.size(); i++) {
vector = convertCoordinates(points2.get(i));
Coords[counter] = vector[0] / vector[3];
Coords[counter+1] = -1 * (vector[1] / vector[3]);
counter= counter+2;
}
}
// initialize vertex Buffer for triangle
ByteBuffer vbb = ByteBuffer.allocateDirect(
// (# of coordinate values * 4 bytes per float)
Coords.length * 4);
vbb.order(ByteOrder.nativeOrder());// use the device hardware's native
// byte order
triangleVB = vbb.asFloatBuffer(); // create a floating point buffer from
// the ByteBuffer
triangleVB.put(Coords); // add the coordinates to the
// FloatBuffer
triangleVB.position(0); // set the buffer to read the first coordinate
}
public void onSurfaceCreated(GL10 unused, EGLConfig config) {
// Set the background frame color
GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
// initialize the triangle vertex array
// initShapes();
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);
initShapes();
// Add program to OpenGL environment
GLES20.glUseProgram(mProgram);
// Prepare the triangle data
GLES20.glVertexAttribPointer(maPositionHandle, 2, GLES20.GL_FLOAT,
false, 0, triangleVB);
GLES20.glEnableVertexAttribArray(maPositionHandle);
// Apply a ModelView Projection transformation
Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mVMatrix, 0);
GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0);
GLES20.glLineWidth(5f);
GLES20.glDrawArrays(GLES20.GL_LINE_STRIP, 0, counter);
}
public void onSurfaceChanged(GL10 unused, int width, int height) {
GLES20.glViewport(0, 0, width, height);
float ratio = (float) width / height;
viewport[0] = 0;
viewport[1] = 0;
viewport[2] = width;
viewport[3] = 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);
}
提前致谢
最佳答案
for (int i = counter/2; i < points2.size(); i++) {
vector = convertCoordinates(points2.get(i));
Coords[counter] = vector[0] / vector[3];
Coords[counter+1] = -1 * (vector[1] / vector[3]);
counter= counter+2;
}
您已初始化 Coords 以容纳 100000 个 float ，并将它们初始化为 0。在此循环中，最后一次迭代具有“计数器”，其中包含您在数组中设置的 float 。
传递给 glDrawArrays 的应该是要绘制的 VERTICES 的数量。所以在这种情况下是“计数器”的一半。
GLES20.glDrawArrays(GLES20.GL_LINE_STRIP, 0, counter);
您的 for 循环在数组的末尾添加了“counter”/2 个额外数量的 (0,0) 顶点。最快的解决方法是将 'counter'/2 传递给 glDrawArrays，但我建议采用更清晰的方法。
numOfVertices = points2.size(); //make field
int counter = 0; //make local
for (int i = 0; i < numOfVertices; i++) {
vector = convertCoordinates(points2.get(i));
Coords[counter] = vector[0] / vector[3];
Coords[counter+1] = -1 * (vector[1] / vector[3]);
counter= counter+2;
}
然后
GLES20.glDrawArrays(GLES20.GL_LINE_STRIP, 0, numOfVertices);
关于android - OpenGL ES 2.0 基于运动画线，线总是从原点开始，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/11015374/