使用 Quartz 2d 对齐网格效果?iphone开发

Snap to grid effect with Quartz 2d? iphone dev(使用 Quartz 2d 对齐网格效果?iphone开发)

问题描述

仍然是 iphone 开发入门者，但正在尝试.

Still an iphone dev starter but trying.

我想让用户触摸屏幕，此时将在视图上放置一个图钉(点).

I would like to have the user touch the screen at which point a pin (dot) will be placed on the view.

我已经完成了这个(是的)，但我想要快速抓握效果，但无法提出解决方案.这就是我放置那个点的方式:

I have accomplished this (yey) but i would like to have snap to grip effect, and can not come up with a solution. This is how i am placing that dot:

CGPoint drawPoint = CGPointMake(lastTouch.x - Horizo​​ntalOffset, lastTouch.y - >verticalOffset);[drawImage drawAtPoint:drawPoint];//告诉图像自己绘制

CGPoint drawPoint = CGPointMake(lastTouch.x - horizontalOffset, lastTouch.y - >verticalOffset); [drawImage drawAtPoint:drawPoint]; //Tell the image to draw itself

我在 Viewcontroller 上有一个网格作为背景，与该网格重叠我有一个带有自定义绘图的 UIView，每次用户触摸屏幕时都会显示一个图钉.

I have a grid as a background on a Viewcontroller, overlapping that grid i have a UIView with custom drawing that displays a pin every time the user touches the screen.

(由于某种原因，点在用户触摸之前就已经出现了......尽管这是我目前正在研究的另一个查询)

(and for some reason the dot already appears before the user touches... all though that is another query that i am looking into at the moment)

所以捕捉到网格效果.有什么想法吗?

So snap to grid effect. Any ideas?

推荐答案

假设你的做法是让用户点击，然后将 pin 放在最近的网格交叉点，这基本上只是一个舍入问题.

Assuming that your approach is to let the user tap, and then put the pin at the closest grid intersection, this is basically just a rounding problem.

// assume these constants
// kVGridOffset, kHGridOffset: the difference between the origin of the view
//   and the origin of the grid
// kVGridSpacing, kHGridSpacing: the size of the grid itself

// set initial coordinates from touch
CGPoint drawPoint = CGPointMake(lastTouch.x - horizontalOffset, lastTouch.y - verticalOffset);

// remove the offset, round to nearest increment of spacing, and return offset
drawPoint.x = floor((drawPoint.x - kHGridOffset) / kHGridSpacing + 0.5) * kHGridSpacing + kHGridOffset;
drawPoint.y = floor((drawPoint.y - kVGridOffset) / kVGridSpacing + 0.5) * kVGridSpacing + kVGridOffset;

// draw the image
[drawImage drawAtPoint:drawPoint];

使用 nearbyint() 进行舍入，事情可能会更整洁一些:

with the availability of nearbyint() for rounding, things can be a little neater:

drawPoint.x = nearbyint((drawPoint.x - kHGridOffset) / kHGridSpacing) * kHGridSpacing + kHGridOffset;
drawPoint.y = nearbyint((drawPoint.y - kVGridOffset) / kVGridSpacing) * kVGridSpacing + kVGridOffset;

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