Question

我正在尝试使用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。

我的非项目代码如下所示：

+ (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;
}

我对它的调用看起来像这样：

- (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：我的gluUnproject总是返回屏幕中间任何位置的几何点，无论我在哪里点击。

修改 “总是靠近中心”问题是返回的X / Z值总是非常接近零，并且我的几何体以原点为中心。

看起来问题出在我的tapZ值上。我的理解是，这应该是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。尝试了各种tapZ值，我看到了：

    // 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，我需要传递正确的tapZ值，但我不明白如何达到它！

Answer 1

好的，哇！事实证明问题是我的tapZ值，问题与深度缓冲区Z值不是线性的事实有关。（更多关于那种祸害here。）

无论如何，使用glProject（）将一个有问题的几何体投影到屏幕上（记住，我正在处理一个平板棋盘的俯视图！），给我一个我想要的z值。最终结果代码如下：

- (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;
}

和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：要求视口的glGet *（）给出正确定位（我的应用是横向）值，这也很重要！

我的GLKMathUnproject总是返回中心屏幕的几何体

1 个答案: