围绕CGContextRef进行绘制以消除像素化 [英] Drawing around CGContextRef to remove pixelation

问题描述

当前，我在绘制小点时遇到图形问题。

Currently, I am having a graphical issue with drawing small dots.

我注意到在大多数专业的Calendar应用程序中，事件日历标识符是一个小点，其颜色是事件日历的颜色。

I notice that in most professional Calendar applications, the events calendar indentifier is a small dot whose color is the events calendar color.

我目前在我的应用程序中需要绘制更好点的位置。这是我的意思的照片。

I am current at the point of my application where I need to draw a BETTER dot. Heres a photo of what I mean.

在这里可能并不明显，但是彩色点在我的手机上时非常像素化。我想消除像素化。

It may not be noticeable here but the colored dot is pretty pixelated when its on my phone. I would like to remove the pixelation.

我浏览了Ray Wenderlich网站上的教程： Ray Wenderlich Core Graphics 。

I went through a tutorial from Ray Wenderlich's website: Ray Wenderlich Core Graphics.

这就是我得到的

UIGraphicsBeginImageContext(cell.imageViewPic.bounds.size);
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(contextRef, [[event calendar] CGColor]);
CGContextFillEllipseInRect(contextRef,(CGRectMake (0.f, 0.f, cell.imageViewPic.bounds.size.width, cell.imageViewPic.bounds.size.height)));

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
cell.imageViewPic.image = image;

因此，这实际上实现了圆，但是我添加了它以在圆周围画一条小线来消除

So this actually implements the circle, but I added this to draw a small line around the circle to rid the pixelation but no go.

CGPoint startPoint = CGPointMake(cell.imageViewPic.frame.origin.x, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
CGPoint endPoint = CGPointMake(cell.imageViewPic.frame.origin.x + cell.imageViewPic.frame.size.width - 1, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
UIColor* color = [UIColor blackColor];
CGContextSaveGState(contextRef);
CGContextSetLineCap(contextRef, kCGLineCapSquare);
CGContextSetStrokeColorWithColor(contextRef, color.CGColor);
CGContextSetLineWidth(contextRef, 10.0);
CGContextMoveToPoint(contextRef, startPoint.x + 0.5, startPoint.y + 0.5);
CGContextAddLineToPoint(contextRef, endPoint.x + 0.5, endPoint.y + 0.5);
CGContextStrokePath(contextRef);
CGContextRestoreGState(contextRef);

所有看起来都是这样...

All together looks like this...

UIGraphicsBeginImageContext(cell.imageViewPic.bounds.size);
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(contextRef, [[event calendar] CGColor]);
CGContextFillEllipseInRect(contextRef,(CGRectMake (0.f, 0.f, cell.imageViewPic.bounds.size.width, cell.imageViewPic.bounds.size.height)));

CGPoint startPoint = CGPointMake(cell.imageViewPic.frame.origin.x, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
CGPoint endPoint = CGPointMake(cell.imageViewPic.frame.origin.x + cell.imageViewPic.frame.size.width - 1, cell.imageViewPic.frame.origin.y + cell.imageViewPic.frame.size.height - 1);
UIColor* color = [UIColor blackColor];
CGContextSaveGState(contextRef);
CGContextSetLineCap(contextRef, kCGLineCapSquare);
CGContextSetStrokeColorWithColor(contextRef, color.CGColor);
CGContextSetLineWidth(contextRef, 10.0);
CGContextMoveToPoint(contextRef, startPoint.x + 0.5, startPoint.y + 0.5);
CGContextAddLineToPoint(contextRef, endPoint.x + 0.5, endPoint.y + 0.5);
CGContextStrokePath(contextRef);
CGContextRestoreGState(contextRef);

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
cell.imageViewPic.image = image;

圆圈仍然画出，但是没有画出笔画。

The circle is still drawn but there is no "stroke" being drawn.

如果有人可以就如何解决此像素化问题提供一些建议，请发布！

If anyone would give some pointers on how this pixelation issue is solved, please post!

推荐答案

发生像素化的原因是，当您创建图像上下文时，没有考虑屏幕比例。您的代码应该是这样的（请注意第一行）：

The pixelation is occurring because when you make the image context you don't take the screen scale into consideration. Your code should be something like this (note the 1st line):

UIGraphicsBeginImageContextWithOptions(cell.imageViewPic.bounds.size, NO, [UIScreen mainScreen].scale)
CGContextRef contextRef = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(contextRef, [[event calendar] CGColor]);
CGContextFillEllipseInRect(contextRef,(CGRectMake (0.f, 0.f, cell.imageViewPic.bounds.size.width, cell.imageViewPic.bounds.size.height)));

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
cell.imageViewPic.image = image;

更新：有人评论时，您可以传递 0 而不是 [UIScreen mainScreen] .scale 。文档同意：

Update: As someone commented, you can pass in 0 instead of [UIScreen mainScreen].scale. The docs agree:

应用于位图的比例因子。如果您将值指定为0.0，则比例因子将设置为设备主屏幕的比例因子。

The scale factor to apply to the bitmap. If you specify a value of 0.0, the scale factor is set to the scale factor of the device’s main screen.

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