OpenGL未将坐标正确映射到android屏幕

Posted 2023-03-05

【中文标题】OpenGL未将坐标正确映射到android屏幕

【英文标题】：OpenGL not mapping coordinates correctly to android screen

【发布时间】：2012-04-25 23:17:50

【问题描述】：

我在将 OpenGL 坐标正确映射到我的 android 屏幕时遇到问题。由于某种原因，x 坐标不包含在屏幕中。当我尝试在屏幕中间绘制一个半径为 x 屏幕一半的圆时，这是可见的。圆圈应该足够大以适合屏幕的 x 边框，但它却超出了屏幕边框，实际上是在触摸屏幕的 y 边框。另外，如果我告诉圆在 0,0（左上角）处绘制，则在将其转换为 OpenGL 坐标后，中心实际上将绘制在 x 边界之外。

希望这是有道理的。

这是我的 DrawScreen 类：

public class DrawScreen implements GLSurfaceView.Renderer 

Ball ball;

public float mAngle;

private int mProgram;
private int maPositionHandle;

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

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";


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);

    ball.initShapes(240, 360, 240);

    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, 12, 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());



public void onSurfaceChanged(GL10 unused, int width, int height) 
    // Set the OpenGL viewport to the same size as the surface.
    GLES20.glViewport(0, 0, width, height);

    // Create a new perspective projection matrix. The height will stay the same
    // while the width will vary as per aspect ratio.
    final float ratio = (float) width / height;
    final float left = ratio;
    final float right = -ratio;
    final float bottom = 1.0f;
    final float top = -1.0f;
    final float near = 3.0f;
    final float far = 7.0f;

    //Matrix.frustumM(mProjMatrix, 0, left, right, bottom, top, near, far);

    Matrix.orthoM(mProjMatrix, 0, left, right, bottom, top, near, far);     

     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;

这里是我将屏幕坐标转换为 OpenGL 坐标的地方：

    float numSegments = 360;

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

    cx = (tx / (480 / 2 )) - 1.f;
    cy = (ty /  (720 / 2 )) - 1.f;

    r = (tr / (480 / 2 )) ;

    System.out.println(r);
    System.out.println(cx);
    System.out.println(cy);

    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

【参考方案1】：

好的，所以我解决了它...虽然它看起来不漂亮。

我基本上把 onSurfaceChanged 中的所有数字都翻到了他们的头上，它看起来就是我现在想要的样子。

这是我的新代码：

public void onSurfaceChanged(GL10 unused, int width, int height) 
    // Set the OpenGL viewport to the same size as the surface.
    GLES20.glViewport(0, 0, width, height);

    // Create a new perspective projection matrix. The height will stay the same
    // while the width will vary as per aspect ratio.
    final float ratio = (float) height / width;
    final float left = 1;
    final float right = -1;
    final float bottom = ratio;
    final float top = -ratio;
    final float near = 3.0f;
    final float far = 7.0f;

    //Matrix.frustumM(mProjMatrix, 0, left, right, bottom, top, near, far);

    Matrix.orthoM(mProjMatrix, 0, left, right, bottom, top, near, far);     

     muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");

     Matrix.setLookAtM(mVMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f);

【讨论】：

哇，说得太早了~现在我有同样的错误，但相反。 X 工作正常，但如果我将 y 设置为 0，则不会一直到顶部。