CGContextDrawAngleGradient？ [英] CGContextDrawAngleGradient?

问题描述

把我的脚放到一些更多的Core Graphics绘图中，我试图重新创建一个邪恶的金属旋钮，我已经登陆了什么可能是一个显示停止的问题。

Dipping my feet into some more Core Graphics drawing, I'm attempting to recreate a wicked looking metallic knob, and I've landed on what is probably a show-stopping issue.

在Core Graphics中似乎没有任何方法绘制 角度 渐变。我看到有 CGContextDrawRadialGradient（）和 CGContextDrawLinearGradient（），但没有什么，角度梯度。有没有人知道一个解决方法，或一些框架隐藏在某处完成这个没有预先渲染旋钮到图像文件？

There doesn't seem to be any way to draw angle gradients in Core Graphics. I see there's CGContextDrawRadialGradient() and CGContextDrawLinearGradient(), but there's nothing that I see that would allow me to draw an angle gradient. Does anyone know of a workaround, or a bit of framework hidden away somewhere to accomplish this without pre-rendering the knob into an image file?

。

推荐答案

是一种抛在一起，但它是我可能会采取的方法。这是创建一个角度渐变，通过使用一些简单的trig直接绘制到位图，然后将其剪切成一个圆。我使用灰度色空间创建一个网格的内存，计算从给定的点到中心的角度，然后基于周期函数，运行在0到255之间的颜色。你当然可以扩展这个做RGBA颜色。

This is kind of thrown together, but it's the approach I'd probably take. This is creating an angle gradient by drawing it directly into a bitmap using some simple trig, then clipping it to a circle. I create a grid of memory using a grayscale colorspace, calculate the angle from a given point to the center, and then color that based on a periodic function, running between 0 to 255. You could of course expand this to do RGBA color as well.

当然，你会缓存这个，玩数学，得到你想要的颜色。这个目前从黑色到白色，这看起来不如你想要的好。

Of course you'd cache this and play with the math to get the colors you want. This currently runs all the way from black to white, which doesn't look as good as you'd like.

- (void)drawRect:(CGRect)rect {
  CGImageAlphaInfo alphaInfo = kCGImageAlphaNone;
  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
  size_t components = CGColorSpaceGetNumberOfComponents( colorSpace );
  size_t width = 100;
  size_t height = 100;
  size_t bitsPerComponent = 8;
  size_t bytesPerComponent = bitsPerComponent / 8;
  size_t bytesPerRow = width * bytesPerComponent * components;
  size_t dataLength = bytesPerRow * height;

  uint8_t data[dataLength];

  CGContextRef imageCtx = CGBitmapContextCreate( &data, width, height, bitsPerComponent,
                                      bytesPerRow, colorSpace, alphaInfo );

  NSUInteger offset = 0;
  for (NSUInteger y = 0; y < height; ++y) {
    for (NSUInteger x = 0; x < bytesPerRow; x += components) {
      CGFloat opposite = y - height/2.;
      CGFloat adjacent = x - width/2.;
      if (adjacent == 0) adjacent = 0.001;
      CGFloat angle = atan(opposite/adjacent);
      data[offset] = abs((cos(angle * 2) * 255));
      offset += components * bytesPerComponent;
    }
  }

  CGImageRef image = CGBitmapContextCreateImage(imageCtx);

  CGContextRelease(imageCtx);
  CGColorSpaceRelease(colorSpace);

  CGContextRef ctx = UIGraphicsGetCurrentContext();

  CGRect buttonRect = CGRectMake(100, 100, width, width);
  CGContextAddEllipseInRect(ctx, buttonRect);
  CGContextClip(ctx);

  CGContextDrawImage(ctx, buttonRect, image);
  CGImageRelease(image);
}

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