Android OpenGL ES 2.0 - 旋轉到位

Question

我想在Z軸上旋轉我的三角形，但我會圍繞三角形的中心而不是屏幕的中心。我已經研究了很多，但沒有找到任何解決方案。

任何想法，我可以嘗試解決它？

public class RendererClass implements Renderer { 

FloatBuffer bufferObj1; 
FloatBuffer bufferObj2; 

int programObj1; 
int programObj2; 

int positionObj1; 
int positionObj2; 

int rotationMatrixLocationObj1; 
int rotationMatrixLocationObj2; 

int colorObj1; 
int colorObj2; 

float[] rotationMatrixObj1 = new float[16]; 
float[] rotationMatrixObj2 = new float[16]; 

@Override 
public void onSurfaceCreated(GL10 arg0, EGLConfig config) { 

    GLES20.glClearColor(0.0f, 1.0f, 1.0f, 1.0f);  

    float[] vertexObj1 = { 

      -0.8f, 0.8f, 
      -0.8f, 0.0f, 
      0.0f, 0.0f 

    }; 

    float[] vertexObj2 = { 

      0.8f, 0.8f, 
      0.8f, 0.0f, 
      0.0f, 0.0f 

    }; 

    bufferObj1 = ByteBuffer.allocateDirect(vertexObj1.length*4).order(ByteOrder.nativeOrder()).asFloatBuffer().put(vertexObj1); 
    bufferObj2 = ByteBuffer.allocateDirect(vertexObj2.length*4).order(ByteOrder.nativeOrder()).asFloatBuffer().put(vertexObj2); 

    String vssObj1 = "attribute vec4 positionObj1;" + 
        "uniform mat4 rotationMatrixObj1;" + 
        "void main(){" + 
        "gl_Position = rotationMatrixObj1 * positionObj1;" + 
        "}"; 

    String vssObj2 = "attribute vec4 positionObj2;" + 
        "uniform mat4 rotationMatrixObj2;" + 
        "void main(){" + 
        "gl_Position = rotationMatrixObj2 * positionObj2;" + 
        "}"; 

    String fssObj1 = "precision mediump float;" + 
        "uniform vec4 colorObj1;" + 
        "void main(){" + 
        "gl_FragColor = colorObj1;" + 
        "}"; 

    String fssObj2 = "precision mediump float;" + 
        "uniform vec4 colorObj2;" + 
        "void main(){" + 
        "gl_FragColor = colorObj2;" + 
        "}"; 

    int vsObj1 = glCreateShader(GL_VERTEX_SHADER); 
    int vsObj2 = glCreateShader(GL_VERTEX_SHADER); 

    int fsObj1 = glCreateShader(GL_FRAGMENT_SHADER); 
    int fsObj2 = glCreateShader(GL_FRAGMENT_SHADER); 

    glShaderSource(vsObj1, vssObj1); 
    glShaderSource(vsObj2, vssObj2); 

    glShaderSource(fsObj1, fssObj1); 
    glShaderSource(fsObj2, fssObj2); 

    glCompileShader(vsObj1); 
    glCompileShader(vsObj2); 

    glCompileShader(fsObj1); 
    glCompileShader(fsObj2); 

    programObj1 = glCreateProgram(); 
    programObj2 = glCreateProgram(); 

    glAttachShader(programObj1, vsObj1); 
    glAttachShader(programObj2, vsObj2); 

    glAttachShader(programObj1, fsObj1); 
    glAttachShader(programObj2, fsObj2); 

    glLinkProgram(programObj1); 
    glLinkProgram(programObj2); 

    positionObj1 = glGetAttribLocation(programObj1, "positionObj1"); 
    positionObj2 = glGetAttribLocation(programObj2, "positionObj2"); 

    rotationMatrixLocationObj1 = glGetUniformLocation(programObj1, "rotationMatrixObj1"); 
    rotationMatrixLocationObj2 = glGetUniformLocation(programObj2, "rotationMatrixObj2");  

    colorObj1 = glGetUniformLocation(programObj1, "colorObj1"); 
    colorObj2 = glGetUniformLocation(programObj2, "colorObj2");  

} 

@Override 
public void onSurfaceChanged(GL10 arg0, int width, int height) { 

    Matrix.setIdentityM(rotationMatrixObj1, 0); 
    Matrix.rotateM(rotationMatrixObj1, 0, MainActivity.angle, 0, 0, 1);  

    Matrix.setIdentityM(rotationMatrixObj2, 0); 
    Matrix.rotateM(rotationMatrixObj2, 0, MainActivity.angle, 0, 0, -1); 

} 

GL10 gl; 

@Override 
public void onDrawFrame(GL10 glUnused) { 

    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);  

    onSurfaceChanged(gl, 0, 0); 

    glUseProgram(programObj1); 
    bufferObj1.position(0); 
    glVertexAttribPointer(positionObj1, 2, GL_FLOAT, false, 0, bufferObj1); 
    glEnableVertexAttribArray(positionObj1); 
    glUniform4f(colorObj1, 0.0f, 0.0f, 1.0f, 1.0f); 
    glUniformMatrix4fv(rotationMatrixLocationObj1, 1, false, rotationMatrixObj1, 0); 
    glDrawArrays(GL_TRIANGLES, 0, 3); 

    glUseProgram(programObj2); 
    bufferObj2.position(0); 
    glVertexAttribPointer(positionObj2, 2, GL_FLOAT, false, 0, bufferObj2); 
    glEnableVertexAttribArray(positionObj2); 
    glUniform4f(colorObj2, 1.0f, 0.0f, 0.0f, 1.0f); 
    glUniformMatrix4fv(rotationMatrixLocationObj2, 1, false, rotationMatrixObj2, 0); 
    glDrawArrays(GL_TRIANGLES, 0, 3); 

} 

} 

Answer 1

您使用glDrawArrays這樣你就可以改變你的三角形在你的代碼，你想要的任何方式。使用簡單的三角函數獨立旋轉頂點。

Answer 2

旋轉矩陣圍繞座標系中心旋轉頂點。 如果你想周圍的一些其他點（X0，Y0，Z0）旋轉的場景，你必須做這3個簡單步驟：

1. 翻譯以這樣的方式的場景，你的觀點將在座標系統的中心（通過-x0，-y0，-z0）
2. 旋轉
3. 轉換回（由X0，Y0，Z0）

當然不需要改造的3個步驟，矩陣乘法可以做這個工作我們。