Question

我有一个实现GLSurfaceView.Renderer接口的渲染器; GLSurfaceView的子类和一些表示我想要绘制的对象的类。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而无法管理它。该对象仅旋转。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，对象将通过mAngle旋转并沿Y轴移动1f。我只能看到旋转（有点投射）。我实际上有一些问题：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存储在渲染器中吗？矩阵运算应该在渲染器类中执行吗？我将它们组合在一起，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，以下方法最终适用于我。（基于Android Training > Displaying Graphics with OpenGL ES > Adding Motion）

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;" +
"}";

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];
[...]

在 onDrawFrame 中应用转换，以翻译开头：

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

然后轮换：

// 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);

合并轮播和翻译，避免使用 mModelMatrix

“作为multiplyMM右侧和左侧的相同矩阵”（见2）

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

将模型矩阵与投影和摄像机视图相结合; 再次避免使用 mModelMatrix

“作为multiplyMM右侧和左侧的相同矩阵”（见2）

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

绘制形状

// Draw shape
mTriangle.draw(mMVPMatrix);

谢谢大家，我可以从这个帖子中得到所有有用的输入。

Answer 2

如果你想看到移动，你应该每帧更新mTriangle.mAngle（最好是时间的函数来对抗由其他进程引起的速度差异或延迟......）。

注意Matrix.setIdentityM（mModelMatrix，0）;将所有累积的旋转和翻译恢复为“零”或实际上恢复到身份矩阵...... 相同的约定将btw应用于所有 set 函数。为了积累所有的变换，必须

setIdentity（模型）;
翻译（反式）; //获取旋转原点
旋转（rotmatrix）; //积累轮换
翻译（T2）; //再次翻译到更好的位置...

还应该在每个调用之间保留对象转换向量[ox，oy，oz]的值，并将它们提供给Matrix.translateM（mModelMatrix，ox，oy，oz，0）;

通常，尽可能早地连接所有“翻译，旋转，缩放”等矩阵，并按每个对象缓存它们，或者按照具有多个对象并具有边界框的复杂容器进行分层，以便可以剔除多个对象当在相机后面（或通常在观看视锥体外）时。

通常一个人将一个移动的摄像机保持在一个矩阵中，每帧将它与投影矩阵相乘。

您可以从以下内容开始：

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

正如蒂姆所注意到的那样，没有涉及投影矩阵，这意味着所有z值都在这个代码中完全表现，即使改变x＆amp; y值会产生影响。

我很想说，MVP矩阵意味着成倍增加按顺序M * V * P =（M * V）* P = M *（V * P）。

Answer 3

请注意，您没有将投影矩阵应用于您正在绘制的三角形，这可能会导致问题。

应该是：

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

OpenGL ES Android矩阵转换

3 个答案: