在ios中的相机覆盖上绘制3D网格

Question

我正在开发一个增强现实应用，我需要在相机叠加层上添加3D网格。到目前为止我的尝试：

DrawLayer.h

#import <UIKit/UIKit.h>

@interface DrawLayer : UIView

@property (nonatomic, assign) int numberOfColumns;
@property (nonatomic, assign) int numberOfRows;
@end

DrawLayer.m

#import "DrawLayer.h"

@implementation DrawLayer

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context, 0.5);
    CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);

    // ---------------------------
    // Drawing column lines
    // ---------------------------

    // calculate column width
    CGFloat columnWidth = self.frame.size.width / (self.numberOfColumns + 1.0);

    for(int i = 1; i <= self.numberOfColumns; i++)
    {
        CGPoint startPoint;
        CGPoint endPoint;

        startPoint.x = columnWidth * i;
        startPoint.y = 0.0f;

        endPoint.x = startPoint.x;
        endPoint.y = self.frame.size.height;

        CGContextMoveToPoint(context, startPoint.x, startPoint.y);
        CGContextAddLineToPoint(context, endPoint.x, endPoint.y);
        CGContextStrokePath(context);
    }

    // ---------------------------
    // Drawing row lines
    // ---------------------------

    // calclulate row height
    CGFloat rowHeight = self.frame.size.height / (self.numberOfRows + 1.0);

    for(int j = 1; j <= self.numberOfRows; j++)
    {
        CGPoint startPoint;
        CGPoint endPoint;

        startPoint.x = 0.0f;
        startPoint.y = rowHeight * j;

        endPoint.x = self.frame.size.width;
        endPoint.y = startPoint.y;

        CGContextMoveToPoint(context, startPoint.x, startPoint.y);
        CGContextAddLineToPoint(context, endPoint.x, endPoint.y);
        CGContextStrokePath(context);
    }
}

@end

并将其添加到相机叠加层

DrawLayer *gridView = [[DrawLayer alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
    gridView.backgroundColor=[UIColor clearColor];
    gridView.numberOfColumns = 10;
    gridView.numberOfRows = 8;
    [gridView setNeedsDisplay];

    CATransform3D t=gridView.layer.transform;
    t.m34 = 1.0 / -300.0;
    t = CATransform3DRotate(t, DEGREES_TO_RADIANS(60.0), 1, 0, 0);
    gridView.layer.transform=t;

    [cameraUI setCameraOverlayView:gridView];

现在我的结果是：

但我希望输出如下：

这段代码有什么问题？请帮忙。