android - 三角形不会旋转

Question

所以我遵循了谷歌的这个教程:http://developer.android.com/resources/tutorials/opengl/opengl-es20.html

三角形应该旋转以响应触摸事件，但没有任何反应。当它应该自己旋转时，它在前面的步骤中也没有旋转。不确定是什么问题。我只是复制了他们的代码。

整个项目只有两个文件:

HelloOpenGLES20Activity.java

package com.opengl.es20;

import android.app.Activity;
import android.content.Context;
import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.view.MotionEvent;

public class HelloOpenGLES20Activity extends Activity {

    private GLSurfaceView mGLView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Create a GLSurfaceView instance and set it
        // as the ContentView for this Activity
        mGLView = new HelloOpenGLES20SurfaceView(this);
        setContentView(mGLView);
    }

    @Override
    protected void onPause() {
        super.onPause();
        // The following call pauses the rendering thread.
        // If your OpenGL application is memory intensive,
        // you should consider de-allocating objects that
        // consume significant memory here.
        mGLView.onPause();
    }

    @Override
    protected void onResume() {
        super.onResume();
        // The following call resumes a paused rendering thread.
        // If you de-allocated graphic objects for onPause()
        // this is a good place to re-allocate them.
        mGLView.onResume();
    }
}

class HelloOpenGLES20SurfaceView extends GLSurfaceView {

    private final float TOUCH_SCALE_FACTOR = 180.0f / 320;
    private HelloOpenGLES20Renderer mRenderer;
    private float mPreviousX;
    private float mPreviousY;

    public HelloOpenGLES20SurfaceView(Context context){
        super(context);

        // Create an OpenGL ES 2.0 context.
        setEGLContextClientVersion(2);
        // set the mRenderer member
        mRenderer = new HelloOpenGLES20Renderer();
        setRenderer(mRenderer);

        // Render the view only when there is a change
        setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);

    }

    @Override 
    public boolean onTouchEvent(MotionEvent e) {
        // MotionEvent reports input details from the touch screen
        // and other input controls. In this case, you are only
        // interested in events where the touch position changed.

        float x = e.getX();
        float y = e.getY();

        switch (e.getAction()) {
            case MotionEvent.ACTION_MOVE:

                float dx = x - mPreviousX;
                float dy = y - mPreviousY;

                // reverse direction of rotation above the mid-line
                if (y > getHeight() / 2) {
                  dx = dx * -1 ;
                }

                // reverse direction of rotation to left of the mid-line
                if (x < getWidth() / 2) {
                  dy = dy * -1 ;
                }

                mRenderer.mAngle += (dx + dy) * TOUCH_SCALE_FACTOR;
                requestRender();
        }

        mPreviousX = x;
        mPreviousY = y;
        return true;
    } 
}

HelloRendererOpenGLES20Renderer.java

package com.opengl.es20;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.Matrix;
import android.os.SystemClock;

public class HelloOpenGLES20Renderer implements GLSurfaceView.Renderer {

    private FloatBuffer triangleVB;
    private final String vertexShaderCode = 
            "uniform mat4 uMVPMatrix;  \n" +
            "attribute vec4 vPosition; \n" +
            "void main(){              \n" +
            " 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 mProgram;
    private int maPositionHandle;
    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];

    public float mAngle;

    public void onSurfaceCreated(GL10 unused, EGLConfig config) {
        int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
        int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
        // Set the background frame color
        GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
        initShapes();

        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 triangle data
        GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false, 12, triangleVB);
        GLES20.glEnableVertexAttribArray(maPositionHandle);

        // Create a rotation for the triangle
//        long time = SystemClock.uptimeMillis() % 4000L;
//        float angle = 0.090f * ((int) time);
        Matrix.setRotateM(mMMatrix, 0, mAngle, 0, 0, 1.0f);
        Matrix.multiplyMM(mMVPMatrix, 0, mVMatrix, 0, mMMatrix, 0);
        Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mMVPMatrix, 0);

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

        // Draw the triangle
        GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 3);
    }

    public void onSurfaceChanged(GL10 unused, int width, int height) {
        GLES20.glViewport(0, 0, width, height);
        float ratio = (float) width/height;
        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 void initShapes(){

        float triangleCoords[] = {
            // X, Y, Z
            -0.5f, -0.25f, 0,
             0.5f, -0.25f, 0,
             0.0f,  0.559016994f, 0
        }; 

        // initialize vertex Buffer for triangle  
        ByteBuffer vbb = ByteBuffer.allocateDirect(
                // (# of coordinate values * 4 bytes per float)
                triangleCoords.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(triangleCoords);    // add the coordinates to the FloatBuffer
        triangleVB.position(0);            // set the buffer to read the first coordinate

    }

    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;
    }

}

Answer 1

    Matrix.setRotateM(mMMatrix, 0, mAngle, 0, 0, 1.0f);
    Matrix.multiplyMM(mMVPMatrix, 0, mVMatrix, 0, mMMatrix, 0);
    Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mMVPMatrix, 0);

    // Apply a ModelView Projection transformation
    Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mVMatrix, 0);

我相信这个最后的 multiplyMM 是你的问题。您正在将 mMVPMatrix 重置为mMVPMatrix = mProjMatrix * mVMatrix，并且您正在丢失将应用旋转的模型转换矩阵 mMMatrix。此外，验证 mAngle 是否为非零。