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//
//  SvGridView.h
//  SvSinglePixel
//
//  Created by xiaoyong.cxy on 6/23/15.
//  Copyright (c) 2015 smileEvday. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface SvGridView : UIView

/**
 * @brief 网格间距，默认30
 */
@property (nonatomic, assign) CGFloat   gridSpacing;

/**
 * @brief 网格线宽度，默认为1 pixel (1.0f / [UIScreen mainScreen].scale)
 */
@property (nonatomic, assign) CGFloat   gridLineWidth;

/**
 * @brief 网格颜色，默认蓝色
 */
@property (nonatomic, strong) UIColor   *gridColor;

@end




//
//  SvGridView.m
//  SvSinglePixel
//
//  Created by xiaoyong.cxy on 6/23/15.
//  Copyright (c) 2015 smileEvday. All rights reserved.
//

#import "SvGridView.h"

#define SINGLE_LINE_WIDTH           (1 / [UIScreen mainScreen].scale)
#define SINGLE_LINE_ADJUST_OFFSET   ((1 / [UIScreen mainScreen].scale) / 2)

@implementation SvGridView

@synthesize gridColor = _gridColor;
@synthesize gridSpacing = _gridSpacing;

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
        
        _gridColor = [UIColor blueColor];
        _gridLineWidth = SINGLE_LINE_WIDTH;
        _gridSpacing = 30;
    }
    
    return self;
}

- (void)setGridColor:(UIColor *)gridColor
{
    _gridColor = gridColor;
    
    [self setNeedsDisplay];
}

- (void)setGridSpacing:(CGFloat)gridSpacing
{
    _gridSpacing = gridSpacing;
    
    [self setNeedsDisplay];
}

- (void)setGridLineWidth:(CGFloat)gridLineWidth
{
    _gridLineWidth = gridLineWidth;
    
    [self setNeedsDisplay];
}


// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextBeginPath(context);
    CGFloat lineMargin = self.gridSpacing;
    
    /**
     *  https://developer.apple.com/library/ios/documentation/2DDrawing/Conceptual/DrawingPrintingiOS/GraphicsDrawingOverview/GraphicsDrawingOverview.html
     * 仅当要绘制的线宽为奇数像素时，绘制位置需要调整
     */
    CGFloat pixelAdjustOffset = 0;
    if (((int)(self.gridLineWidth * [UIScreen mainScreen].scale) + 1) % 2 == 0) {
        pixelAdjustOffset = SINGLE_LINE_ADJUST_OFFSET;
    }
    
    CGFloat xPos = lineMargin - pixelAdjustOffset;
    CGFloat yPos = lineMargin - pixelAdjustOffset;
    while (xPos < self.bounds.size.width) {
        CGContextMoveToPoint(context, xPos, 0);
        CGContextAddLineToPoint(context, xPos, self.bounds.size.height);
        xPos += lineMargin;
    }
    
    while (yPos < self.bounds.size.height) {
        CGContextMoveToPoint(context, 0, yPos);
        CGContextAddLineToPoint(context, self.bounds.size.width, yPos);
        yPos += lineMargin;
    }
    
    CGContextSetLineWidth(context, self.gridLineWidth);
    CGContextSetStrokeColorWithColor(context, self.gridColor.CGColor);
    CGContextStrokePath(context);
}


@end



//使用方法如下：
SvGridView *gridView = [[SvGridView alloc] initWithFrame:self.view.bounds];
gridView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
gridView.alpha = 0.6;
gridView.gridColor = [UIColor greenColor];
[self.view addSubview:gridView];