Question

我开始在android上学习OpenGL，现在我正试图搞乱一个简单的三角形我正在尝试做的是让它旋转到位（旋转枢轴是形状的中心），虽然我只是设法让它绕轴旋转（我的意思是它在指定的轴上进行圆周运动）。

这是我的代码：

@Override
public void onDrawFrame(GL10 gl) {
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);

    Matrix.setLookAtM(mViewMatrix, 0, 0, 0, -10, 0f, 0f, 0f, 0f, 1.0f, 0.0f);

    long time = SystemClock.uptimeMillis() % 4000L;
    float angle = 0.090f * ((int) time);

    Matrix.setIdentityM(mModelMatrix, 0); // initialize to identity matrix
    Matrix.rotateM(mModelMatrix, 0, angle, 0, 1.0f, 0);

    Matrix.multiplyMM(mMVPMatrix, 0, mViewMatrix, 0, mModelMatrix, 0);
    Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0);

    mPlayerCharacter.draw(mMVPMatrix);
}

@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
    GLES20.glViewport(0, 0, width, height);

    float ratio = (float) width / height;
    Matrix.frustumM(mProjectionMatrix, 0, -ratio, ratio, -1, 1, 3, 7);
}

@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
    GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

    mPlayerCharacter = new PlayerCharacter();
}

----- PlayerCharacter.draw() -----

public void draw(float[] mvpMatrix) {
    // Add program to OpenGL ES 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");

    // Pass the projection and view transformation to the shader
    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);

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

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

三角形坐标为顶部（0,0.622,0），左下角（-0.5，-0.311,0）和右下角（0.5，-0.311,0）。

我尝试寻找类似的问题或相关指南，但我找到的答案都没有为我工作。

如果是这样，实现我正在寻找的结果的正确方法是什么？

Answer 1

假设您有对象转换矩阵：

    protected final float[] mTransformMatrix = new float[16];

创建对象时，只需使用Matrix.setIdentityM(mTransformMatrix, 0);

要旋转，您需要：

Matrix.rotateM(mTransformMatrix, 0, angle, 0, 0, 1.0f);

以下是对象定位，尺寸和旋转的一些方法：

    public Sprite setSize(float sizeX, float sizeY) {
    setCenterSizeRotation(this.mPositionX, this.mPositionY, sizeX, sizeY,
            this.mAngle);
    this.mSpriteWidth = sizeX;
    this.mSpriteHeight = sizeY;

    return this;
}

public Sprite setCenter(float posX, float posY) {
    setCenterSizeRotation(posX, posY, this.mSpriteWidth,
            this.mSpriteHeight, this.mAngle);
    this.mPositionX = posX;
    this.mPositionY = posY;

    return this;
}

public Sprite setRotation(float angle) {
    setCenterSizeRotation(this.mPositionX, this.mPositionY,
            this.mSpriteWidth, this.mSpriteHeight, angle);
    this.mAngle = angle;

    return this;
}

public Sprite setCenterSizeRotation(float posX, float posY, float sizeX,
        float sizeY, float angle) {

    reset();
    float oX = UtilsGL.getStepX() * posX - 1.0f;
    float oY = UtilsGL.getStepY() * posY - 1.0f;
    float scaleX = sizeX / (UtilsGL.getSurfaceWidth());
    float scaleY = sizeY / (UtilsGL.getSurfaceHeight());

    translate(oX, oY);
    scale(scaleX, scaleY);
    rotate(angle);

    this.mSpriteWidth = sizeX;
    this.mSpriteHeight = sizeY;
    this.mPositionX = posX;
    this.mPositionY = posY;
    this.mAngle = angle;

    return this;
}

public Sprite translate(float x, float y) {
    Matrix.translateM(mTransformMatrix, 0, x, y, 0);
    return this;
}

public Sprite scale(float x, float y) {
    Matrix.scaleM(mTransformMatrix, 0, x, y, 1.0f);
    return this;
}

public Sprite rotate(float d) {
    Matrix.rotateM(mTransformMatrix, 0, d, 0, 0, 1.0f);
    return this;
}

public Sprite reset() {
    Matrix.setIdentityM(mTransformMatrix, 0);
    return this;
}

不要害怕退货，这只是我的Sprite类的一些代码

UtilsGL部分：

    private static int mSurfaceWidth;
private static int mSurfaceHeight;
private static float mStepX;
private static float mStepY;

    public static void setSurfaceWH(int width, int height) {
    mSurfaceWidth = width;
    mSurfaceHeight = height;
    mStepX = 2.0f / (float) mSurfaceWidth;
    mStepY = 2.0f / (float) mSurfaceHeight;
}

public static int getSurfaceWidth() {
    return mSurfaceWidth;
}

public static int getSurfaceHeight() {
    return mSurfaceHeight;
}

public static float getStepX() {
    return mStepX;
}

public static float getStepY() {
    return mStepY;
}

这里有很多代码，但它们都很有用。静电为什么？我不是OOP极客）我选择让它变得简单但功能齐全

Answer 2

问题解决了！我简直不敢相信这么小！

问题在于这一行：
gl_Position = vPosition * uMVPMatrix;

我无法解释为什么（所以如果有人可以 - 那就太好了！）但是当我把它改为： gl_Position = uMVPMatrix * vPosition;它按预期工作了！

如果有人能够进一步解释为什么这样做而不是第一个选项，那就太棒了！我当然会将答案标记为已接受。

感谢。

在Android上使用OpenGL ES使对象/形状旋转到位

2 个答案: