用onTouch Android绘制OpenGL ES2.0线

Question

@Override
public boolean onTouchEvent(MotionEvent e) {
    mScaleDetector.onTouchEvent(e);

    switch (e.getAction()) {
        case MotionEvent.ACTION_DOWN: {
            float x = e.getX();
            float y = e.getY();

            mPreviousX = x;
            mPreviousY = y;

            // Save the ID of this pointer
            mActivePointerId = e.getPointerId(0);

            break;
        }

        case MotionEvent.ACTION_MOVE: {

            final int pointerIndex = e.findPointerIndex(mActivePointerId);
            final float x = e.getX(pointerIndex);
            final float y = e.getY(pointerIndex);

            if (!mScaleDetector.isInProgress()) {

                mRenderer.setLineCoordinates(mPreviousX, mPreviousY, x, y);
                requestRender();
            }

            mPreviousX = x;
            mPreviousY = y;

            break;
        }

        case MotionEvent.ACTION_UP: {
            mActivePointerId = INVALID_POINTER_ID;
            break;
        }

        case MotionEvent.ACTION_CANCEL: {
            mActivePointerId = INVALID_POINTER_ID;
            break;
        }

        case MotionEvent.ACTION_POINTER_UP: {
            final int pointerIndex = (e.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) 
                    >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
            final int pointerId = e.getPointerId(pointerIndex);
            if (pointerId == mActivePointerId) {
                // This was our active pointer going up. Choose a new
                // active pointer and adjust accordingly.
                final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                mPreviousX = e.getX(newPointerIndex);
                mPreviousY = e.getY(newPointerIndex);
                mActivePointerId = e.getPointerId(newPointerIndex);
            }
            break;
        }
    }

    return true;
}

在我的呈现器类上：

public void onDrawFrame(GL10 gl) {
    // Draw background color
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

    // Set GL_MODELVIEW transformation mode
    gl.glMatrixMode(GL10.GL_MODELVIEW);
    gl.glLoadIdentity();   // reset the matrix to its default state

    // When using GL_MODELVIEW, you must set the view point
    GLU.gluLookAt(gl, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f);

    gl.glScalef(factor, factor, 0.0f);

    // Draw triangle
    mTriangle.draw(gl);
    mLine.draw(gl);
}

函数在呈现器类中更改坐标：

public void setLineCoordinates(float mPreviousX
        , float mPreviousY, float x, float y) {
    // TODO Auto-generated method stub

    lineCoords[0] = (float) (mPreviousX * 2.0 / WIDTH - 1.0);
    lineCoords[1] = (float) (mPreviousY * -2.0 / HEIGHT + 1.0);
    lineCoords[2] = 0.0f;
    lineCoords[3] = (float) (x * 2.0 / WIDTH - 1.0);
    lineCoords[4] = (float) (y * -2.0 / HEIGHT + 1.0);
    lineCoords[5] = 0.0f;

}

当我移动手指时，没有线，只有一条移动的小线...我怎样才能画出整条线，并在我不断移动手指的同时保持线描？当我再次触屏时，也开始新的一行。

public void setLineCoordinates(float mPreviousX
        , float mPreviousY, float x, float y) {
    // TODO Auto-generated method stub

    float lineCoords[] = new float[6];
    lineCoords[0] = (float) (mPreviousX * 2.0 / WIDTH - 1.0);
    lineCoords[1] = (float) (mPreviousY * -2.0 / HEIGHT + 1.0);
    lineCoords[2] = 0.0f;
    lineCoords[3] = (float) (x * 2.0 / WIDTH - 1.0);
    lineCoords[4] = (float) (y * -2.0 / HEIGHT + 1.0);
    lineCoords[5] = 0.0f;

    bufferOfArrays.add(new Line(lineCoords));

    if(isFirst) {
        isFirst = false;
        listOfArrays.addAll(bufferOfArrays);
        view.requestRender();
    }

}

public void setFirst(boolean isFirst) {
    this.isFirst = isFirst;
}

@Override
public void onDrawFrame(GL10 gl) {
    //... color, matrix, look at etc..

    // Draw triangle
    //mTriangle.draw(gl);
    //TODO mLine.draw(gl);

    for(Line line : listOfArrays) {
        line.draw(gl);
    }
    isFirst = true;

}

Answer 1

这里的问题是，您总是在每一步都设置mPreviousX和mPreviousY。实际上，问题始于您为这些参数选择的名称。更好的名称是mlinestartx/y。

设置mlineStartx/y，然后每次移动都更新x/y，不要更改mlineStartx/y。

至于添加多行，您需要实现更多的逻辑。您需要维护您定义的具有2point(2xpointfs)的某个类的数组列表。当用户举起手指（touch up/touch cancel）时，用2点创建一个新的类，在render方法上，确保遍历所有这样的行并呈现它们。