探讨iOS某个像素点是否显示依据，以摸索为什么iOS没适配的应用在iphone6上面线的粗细会不稳定。有的线会变粗。

先说一下系统对某个像素点是否显示的依据：

// 如果单个像素分为10格，如上图，从上往下第5格被填充或从右往左第5格被填充，则该像素就会被显示；实际上系统会划分的更细，不只是10格。

// 下面是横向的测试代码，需要在2倍屏上测试。
UIView *line = [[UIViewalloc]initWithFrame:CGRectMake(0,10,320,0.25)];//显示

line.backgroundColor = [UIColorredColor];
[_baseContentaddSubview:line];

line = [[UIViewalloc]initWithFrame:CGRectMake(0,12,320,0.2)];//不会显示

line.backgroundColor = [UIColorblueColor];
[_baseContentaddSubview:line];

line = [[UIViewalloc]initWithFrame:CGRectMake(0,14.25,320,0.05)];//不会显示

line.backgroundColor = [UIColorblackColor];
[_baseContentaddSubview:line];

line = [[UIViewalloc]initWithFrame:CGRectMake(0,16.2,320,0.05)];//显示

line.backgroundColor = [UIColorgreenColor];
[_baseContentaddSubview:line];

// 下面是纵向的测试代码

line = [[UIViewalloc]initWithFrame:CGRectMake(10,0,0.255,300)];//显示

line.backgroundColor = [UIColorredColor];
[_baseContentaddSubview:line];

line = [[UIViewalloc]initWithFrame:CGRectMake(12,0,0.25,300)];//不会显示

line.backgroundColor = [UIColorblueColor];
[_baseContentaddSubview:line];

line = [[UIViewalloc]initWithFrame:CGRectMake(14.25,0,0.05,300)];//显示

line.backgroundColor = [UIColorblackColor];
[_baseContentaddSubview:line];

line = [[UIViewalloc]initWithFrame:CGRectMake(16.2,0,0.05,300)];//不会显示

line.backgroundColor = [UIColorgreenColor];
[_baseContentaddSubview:line];

总结：当设置的线如果是1px的时候无论起点在哪里，都只会显示1px的线。
但是如果线超过了1px，比如说1.2px。那么起点的位置就有可能导致线变成2px。

// 下面是测试代码，宽度设置相同，上面是1px，下面是2px。也是在2倍屏上

line = [[UIViewalloc]initWithFrame:CGRectMake(18,0,0.6,300)];//1px

line.backgroundColor = [UIColoryellowColor];
[_baseContentaddSubview:line];

line = [[UIViewalloc]initWithFrame:CGRectMake(22.2,0,0.6,300)];//2px

line.backgroundColor = [UIColoryellowColor];
[_baseContentaddSubview:line];
明白了这个道理，就不难理解为什么没适配的应用在iphone6上面线有可能会变粗。因为0.5个点宽的线在iphone6上面线宽像素会变成1.几px。有时候就有可能显示成2px。