android - OpenGL ES Android 矩阵转换

Question

我有一个实现 GLSurfaceView.Renderer 接口(interface)的渲染器； GLSurfaceView 的一个子类和一些代表我要绘制的对象的类。我有来自 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。对象仅旋转。 这是我的代码:

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，在每次重绘时，对象都会旋转 mAngle，并沿 Y 轴平移 1f。不过，我只能看到旋转(也有点投影)。 我实际上对此有一些疑问: 我如何应用我的翻译矩阵和 划分 opengl 功能的最佳做法是什么？ modelMatrix 不应该存储在对象本身而不是渲染器中吗？矩阵运算应该在渲染器类中执行吗？ 我将它们归为一组，因为我猜它们都是相关的。

Answer 1

我一直在使用 Android 培训中的示例，以下方法最终对我有用。 (基于 Android Training > Displaying Graphics with OpenGL ES > Adding Motion )

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. 在渲染器类中:

   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. 在 onDrawFrame 中应用转换，从翻译开始:

   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. 结合旋转和平移，避免使用mModelMatrix

   "as the same matrix on the right and left side of multiplyMM" (see 2)

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

6. 将模型矩阵与投影和相机 View 相结合； 再次避免使用mModelMatrix

   "as the same matrix on the right and left side of multiplyMM" (see 2)

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

7. 画出形状

   // Draw shape
   mTriangle.draw(mMVPMatrix);
   

谢谢大家，我可以从这个线程中获得所有有用的输入。