OpenGL ES Android矩阵转换

Question

我有一个实现GLSurfaceView.Renderer接口的呈现器; GLSurfaceView的子类和一些代表我想要绘制的对象的类。我有http://developer.android.com/training/graphics/opengl/motion.html 的代码我想扩展它，并添加一些沿轴移动，但无法管理它。该对象只能旋转。 这里是我的代码：

public class NotMyCoolRenderer implements GLSurfaceView.Renderer { 

public GLShip mTriangle; 
private GLBackgroundStar mSquare; 

private final float[] mMVPMatrix = new float[16]; 
private final float[] mProjMatrix = new float[16]; 
private final float[] mVMatrix = new float[16]; 
private final float[] mModelMatrix = new float[16]; 
private final float[] tempMatrix = new float[16]; 

public void onDrawFrame(GL10 unused) { 
    // Draw background color 
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT); 
    // Set the camera position (View matrix) 
    Matrix.setLookAtM(mVMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f); 
    // Calculate the projection and view transformation 
    Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mVMatrix, 0); 
    // Draw square 
    mSquare.draw(mMVPMatrix); 
    // Now moving on to triangle aka ship 
    Matrix.setIdentityM(mModelMatrix, 0); 
    Matrix.translateM(mModelMatrix, 0, 0.1f, 0f, 0); 
    Matrix.rotateM(mModelMatrix, 0, mTriangle.mAngle, 0, 0, -1.0f); 
    Matrix.multiplyMM(tempMatrix, 0, mVMatrix, 0, mProjMatrix, 0); 
    Matrix.multiplyMM(mMVPMatrix, 0, mModelMatrix , 0, tempMatrix , 0); 

    // Draw triangle 
    mTriangle.draw(mMVPMatrix); 
} 
public void onSurfaceChanged(GL10 unused, int width, int height) { 
    // Adjust the viewport based on geometry changes, 
    // such as screen rotation 
    GLES20.glViewport(0, 0, width, height); 

    float ratio = (float) width/height; 

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

} 

public class GLShip { 
    public volatile float mAngle; 
    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;" + 

     "attribute vec4 vPosition;" + 
     "void main() {" + 
     // the matrix must be included as a modifier of gl_Position 
     " gl_Position = uMVPMatrix * vPosition;" + 
     "}"; 


    public void draw(float[] mvpMatrix) { 
     // Add program to OpenGL environment 
     GLES20.glUseProgram(mProgram); 

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

     // Enable a handle to the triangle vertices 
     GLES20.glEnableVertexAttribArray(mPositionHandle); 

     // Prepare the triangle coordinate data 
     GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, 
            GLES20.GL_FLOAT, false, 
            vertexStride, vertexBuffer); 

     // get handle to fragment shader's vColor member 
     mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor"); 

     // Set color for drawing the triangle 
     GLES20.glUniform4fv(mColorHandle, 1, color, 0); 

     // get handle to shape's transformation matrix 
     mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix"); 
     NotMyCoolRenderer.checkGlError("glGetUniformLocation"); 

     // Apply the projection and view transformation 
     GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0); 
     NotMyCoolRenderer.checkGlError("glUniformMatrix4fv"); 

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

     // Disable vertex array 
     GLES20.glDisableVertexAttribArray(mPositionHandle); 
    } 
} 

我的期望是每个重绘对象将通过裂伤旋转和1F沿Y轴traslated。虽然我只能看到旋转（也有点投影）。 我其实有一些问题： 如何应用我的翻译矩阵和 分割opengl功能的最佳做法是什么？模型矩阵不应该存储在对象本身而不是渲染器中？矩阵操作是否应该在渲染器类中执行？ 我将它们分组在一起，因为我猜它们都是相关的。

Answer 1

从来就一直与从Android培训的例子，下面的方法终于为我工作。 （上Android Training > Displaying Graphics with OpenGL ES > Adding Motion基于）

1. 使用正确的顶点着色器：

   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;" + 
   "attribute vec4 vPosition;" + 
   "void main() {" + 
   // the matrix must be included as a modifier of gl_Position 
   " gl_Position = uMVPMatrix * vPosition;" + 
   "}"; 
   

2. 在渲染器类：

   public class MyGL20Renderer implements GLSurfaceView.Renderer { 
   [...] 
   // create a model matrix for the triangle 
   private final float[] mModelMatrix = new float[16]; 
   // create a temporary matrix for calculation purposes, 
   // to avoid the same matrix on the right and left side of multiplyMM later 
   // see https://stackoverflow.com/questions/13480043/opengl-es-android-matrix-transformations#comment18443759_13480364 
   private float[] mTempMatrix = new float[16]; 
   [...] 
   

3. 应用转换在onDrawFrame，开始翻译：

   public void onDrawFrame(GL10 unused) { 
   [...] 
   Matrix.setIdentityM(mModelMatrix, 0); // initialize to identity matrix 
   Matrix.translateM(mModelMatrix, 0, -0.5f, 0, 0); // translation to the left 
   

4. 然后旋转：

   // Create a rotation transformation for the triangle 
   long time = SystemClock.uptimeMillis() % 4000L; 
   float mAngle = 0.090f * ((int) time); 
   Matrix.setRotateM(mRotationMatrix, 0, mAngle, 0, 0, -1.0f); 
   

5. 联合旋转和平移，忌用mModelMatrix

   “的右侧和左侧的同一矩阵乘以MM“（见2）

   // Combine Rotation and Translation matrices 
   mTempMatrix = mModelMatrix.clone(); 
   Matrix.multiplyMM(mModelMatrix, 0, mTempMatrix, 0, mRotationMatrix, 0); 
   

6. 结合与投影和相机视图的模型矩阵; 再次避免使用mModelMatrix

   “作为multiplyMM的右侧和左侧相同的基质”（见2）

   // Combine the model matrix with the projection and camera view 
   mTempMatrix = mMVPMatrix.clone(); 
   Matrix.multiplyMM(mMVPMatrix, 0, mTempMatrix, 0, mModelMatrix, 0); 
   

7. 绘制形状

   // Draw shape 
   mTriangle.draw(mMVPMatrix); 
   

谢谢大家，我可以从这个主题中得到所有有用的输入。

Answer 2

如果你想看到移动，你应该更新mTriangle.mAngle每帧（最好作为时间的函数来对抗由其他进程造成的速度差异或延迟...）。

请注意Matrix.setIdentityM（mModelMatrix，0）;将所有积累的旋转和平移恢复为“零”或实际上恢复到标识矩阵... 同样的惯例适用于btw全部设置函数。 为了积累所有的转化，人们必须

• setIdentity（模型）;
• translate（trans）; //获取旋转的原点
• rotate（rotmatrix）; //积累旋转
• translate（t2）; //再次转化为一些更好的位置...

还应该保持每个调用之间的对象转换矢量[牛，OY，盎司]的值，并喂它们Matrix.translateM（mModelMatrix，牛， oy，oz，0）;

通常，尽可能早地连接所有的'平移，旋转，缩放'等矩阵，并将它们缓存在每个对象上，或者对每个具有多个对象并具有边界框的复杂容器分层存储，以便多个对象可以在相机后面（或通常在观看平截头体之外）时扑灭。

通常还有一个移动摄像机保持在一个矩阵中，并且每帧将其与投影矩阵相乘。

你可以像开始：

float Time = System.currentTimeMillis() * 0.01f; // 10 radians/second == fast! 
Matrix.translateM(mModelMatrix, Math.sin(Time)*2.0f, 0, 1f, 0); 
... 

蒂姆注意到，没有涉及投影矩阵，这意味着所有的Z值在这段代码的行为完全，即使改变x & y值将使一个区别。我很想说MVP矩阵意味着按照M * V * P =（M * V）* P = M *（V * P）的顺序乘以 。

Answer 3

请注意，您并未将投影矩阵应用于您绘制的三角形，这可能会导致问题。

大概应该是：

Matrix.multiplyMM(mMVMatrix, 0, mVMatrix, 0, mModelMatrix, 0); 
Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mMVMatrix, 0);