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我正在尝试GLKMathUnproject()将屏幕坐标转换为几何图形，但我的例程总是返回屏幕中心的任何几何图形。

我的 unproject 代码如下所示：

+ (GLKVector3) gluUnproject: (GLKVector3) screenPoint
                     inView: (UIView*) view
            withModelMatrix: (GLKMatrix4) model
                 projection: (GLKMatrix4) projection
{
    CGSize viewSize = view.bounds.size;
    int viewport[4];
    viewport[0] = 0.0f;
    viewport[1] = 0.0f;
    viewport[2] =  viewSize.width;
    viewport[3] =  viewSize.height;

    bool success;
    GLKVector3 result = GLKMathUnproject(screenPoint, model, projection, &viewport[0], &success);

    return result;
}

我对它的调用如下所示：

- (void) handleSingleTap: (UIGestureRecognizer*) sender
{
    UITapGestureRecognizer *tapper = (UITapGestureRecognizer*) sender;
    CGPoint tapPoint = [tapper locationInView: self.view];

    // Find tapped point on geometry
    MyObject *bd = [worldObjects objectAtIndex: 0];  // the object on which I'm trying to sense the tap.
    // NOTE: bd is planar, along X/Z, with Y=0.  Visually, it's several little
    // ..squares (like a big checkerboard), and I'm trying to determine
    // ..in which square the user tapped.
    // At this point. eyesAt is { someX, y, someZ } and lookAt is { someX, 0, someZ } and
    // ..upVector is { 0, 0, -1 }.  We Zoom our view of the board in/out by
    // ..changing eyesAt.y
    float tapZ = (self.eyesAt.y - self.zNear) / (self.zFar - self.zNear);  // % of the Z-depth.  eyesAt.y = distance to geometry.
    GLKVector3 tapPoint3 = GLKVector3Make(tapPoint.x, tapPoint.y, tapZ);
    GLKVector3 tapAt = [MFglkUtils gluUnproject: tapPoint3 inView: self.view withModelMatrix: bd.modelviewMatrix projection: [self projectionMatrix]];
    // etc., snip -- do stuff with the tapAt point.

问题是：gluUnproject无论我点击哪里，我总是返回屏幕中间的几何点。

编辑： “总是靠近中心”的问题是返回的 X/Z 值总是非常接近于零，并且我的几何图形以原点为中心。

看来问题出在我的tapZ价值上。我的理解是，这应该是一个 0-1 的值，其中 0 表示“在 nearZ 平面”，1 表示“在 farZ 平面”，中间值是介于两者之间的百分比。尝试各种tapZ值，我已经看到：

    // gives very-very small results
    tapZ = (self.eyesAt.y - self.zNear) / (self.zFar - self.zNear); // % deep through the view frustum 

    // gives Z=0, and very small results
    glReadPixels(viewPoint.x, viewPoint.y, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &tapZ);

    // gives approximately-correct results
    tapZ = 0.99943;  // found through trial & error

    // gives Z=1, and too-big results
    glReadPixels(viewPoint.x, viewPoint.y, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &tapZ);
    tapZ = 1. - tapZ;

显然，我需要传递一个正确的tapZ值，但我不明白如何得出它！

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1 回答 1

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好的，哇！事实证明，问题出在我的 tapZ 值上，问题与深度缓冲区 Z 值不是线性的事实有关。（更多关于这里的古怪之处。）

无论如何，使用 glProject() 将有问题的几何图形投影到屏幕上（请记住，我正在处理平面棋盘的俯视图！），给了我想要的 z 值。最终结果代码是这样的：

- (GLKVector3) vectorFromTapPoint: (CGPoint) tapPoint
{
    tapPoint.y = (self.view.bounds.size.height - tapPoint.y);

    BlockDiagram *bd = [worldObjects objectAtIndex: 0];

    // find Z-depth of center of board
    GLKVector3 v3Zero = { 0, 0, 0 };
    int viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport);
    GLKVector3 worldZero = GLKMathProject(v3Zero, bd.modelviewMatrix, [self projectionMatrix], viewport);

    // Find tapped point on geometry
    float tapZ = worldZero.z;
    GLKVector3 tapPoint3 = GLKVector3Make(tapPoint.x, tapPoint.y, tapZ);
    GLKVector3 tapAt = [MFglkUtils gluUnproject: tapPoint3 inView: self.view withModelMatrix: bd.modelviewMatrix projection: [self projectionMatrix]];

    return tapAt;
}

并且 gluUnProject 被修改为：

+ (GLKVector3) gluUnproject: (GLKVector3) screenPoint
                     inView: (UIView*) view
            withModelMatrix: (GLKMatrix4) model
                 projection: (GLKMatrix4) projection
{
    int viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport);

    bool success;
    GLKVector3 result = GLKMathUnproject(screenPoint, model, projection, &viewport[0], &success);

    return result;
}

注意：向 glGet*() 询问视口给出了正确定向的（我的应用程序是横向的）值，这也很重要！

于 2013-06-07T02:31:00.447 回答