ios - 为什么我的 CGImage 在 setNeedsDisplay 后无法正确显示
<p><p>我正在我的应用程序中绘制一个 colorWheel。我通过在单独的函数中生成 CGImage 并在 drawRect 中使用 CGContextDrawImage 将其放在屏幕上来做到这一点。</p>
<p>在最初的演示中,它看起来不错,但在我调用 setNeedsDisplay(或 setNeedsDisplayInRect)之后,图像变黑/失真。我一定在做一些愚蠢的事情,但看不到什么。</p>
<p> <img src="https://i.imgur.com/TiZDuaw.png" alt="Cool Wheel"/>
<img src="https://i.imgur.com/jrQDtqn.png" alt="Cool Wheel"/> </p>
<p>DrawRect 代码如下:</p>
<pre><code>override func drawRect(rect: CGRect) {
if let context = UIGraphicsGetCurrentContext() {
let wheelFrame = CGRectMake(0,0,circleRadius*2,circleRadius*2)
CGContextSaveGState(context)
//create clipping mask for circular wheel
CGContextAddEllipseInRect(context, wheelFrame)
CGContextClip(context)
//draw the wheel
if colorWheelImage != nil { CGContextDrawImage(context, CGRectMake(0,0,circleRadius*2,circleRadius*2), colorWheelImage) }
CGContextRestoreGState(context)
//draw a selector element
self.drawSliderElement(context)
}
}
</code></pre>
<p>CG图像生成函数:</p>
<pre><code>func generateColorWheelImage() {
let width = Int(circleRadius*2)
let height = Int(circleRadius*2)
var pixels = ()
for yIndex in 0..<width {
for xIndex in 0..<height {
pixels.append(colorAtPoint(CGPoint(x: xIndex, y: yIndex)))
}
}
let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo.ByteOrderDefault
let bitsPerComponent: Int = 8
let bitsPerPixel: Int = 24
let renderingIntent = CGColorRenderingIntent.RenderingIntentDefault
assert(pixels.count == Int(width * height))
var data = pixels
let providerRef = CGDataProviderCreateWithData(nil, data, data.count * sizeof(PixelData), nil)
colorWheelImage = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, width * Int(sizeof(PixelData)), rgbColorSpace, bitmapInfo, providerRef, nil, true,renderingIntent)
}
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>当我开始在 ipad 而不是模拟器上运行代码并收到 BAD_ACCESS_ERROR,而不是看到扭曲的图像时,我终于找到了这个问题的答案(这里:<a href="https://stackoverflow.com/a/10798750/5233176" rel="noreferrer noopener nofollow">https://stackoverflow.com/a/10798750/5233176</a>)。</p>
<p>正如答案所解释的:' CMSampleBuffer 直接用于创建 CGImageRef,因此一旦释放缓冲区, CGImageRef 将变得无效。'</p>
<p>因此问题出在这一行:</p>
<pre><code> let providerRef = CGDataProviderCreateWithData(nil, data, data.count * sizeof(PixelData), nil)
</code></pre>
<p>并且可以通过使用缓冲区的副本来解决问题,如下所示:</p>
<pre><code> let providerData = NSData(bytes: data, length: data.count * sizeof(PixelData))
let provider = CGDataProviderCreateWithCFData(providerData)
</code></pre></p>
<p style="font-size: 20px;">关于ios - 为什么我的 CGImage 在 setNeedsDisplay 后无法正确显示,我们在Stack Overflow上找到一个类似的问题:
<a href="https://stackoverflow.com/questions/37773844/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/37773844/
</a>
</p>
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