iOS 截屏，openGL ES 截图，以及像素颜色判断

代码整理了2种截图，类似。（没苹果自带那种截图彻底)

方法一：

+(UIImage *)fullScreenshots{
    
    UIWindow *screenWindow = [[UIApplication sharedApplication] keyWindow];
    //    UIGraphicsBeginImageContext(screenWindow.frame.size);//全屏截图，包括window
    UIGraphicsBeginImageContextWithOptions(screenWindow.frame.size,YES,0.0);
    [screenWindow.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return viewImage;
    
}

　　方法二：

+ (UIImage*)screenShot
{
    // Create a graphics context with the target size
    // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
    // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
    CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    // Iterate over every window from back to front
    for (UIWindow *window in [[UIApplication sharedApplication] windows])
    {
        if ( [window screen] == [UIScreen mainScreen])
        {
            // -renderInContext: renders in the coordinate space of the layer,
            // so we must first apply the layer's geometry to the graphics context
            CGContextSaveGState(context);
            // Center the context around the window's anchor point
            CGContextTranslateCTM(context, [window center].x, [window center].y);
            // Apply the window's transform about the anchor point
            CGContextConcatCTM(context, [window transform]);
            // Offset by the portion of the bounds left of and above the anchor point
            CGContextTranslateCTM(context,
                                  -[window bounds].size.width * [[window layer] anchorPoint].x,
                                  -[window bounds].size.height * [[window layer] anchorPoint].y);
            
            // Render the layer hierarchy to the current context
            [[window layer] renderInContext:context];
            
            // Restore the context
            CGContextRestoreGState(context);
        }
    }
    
    // Retrieve the screenshot image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    return image;
}　

openGL ES 截图

- (UIImage*) takePicture {
    int s = 1;
    UIScreen* screen = [UIScreen mainScreen];
    if ([screen respondsToSelector:@selector(scale)]) {
        s = (int) [screen scale];
    }
    
    GLint viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport);
    
    
    int width = viewport[2];
    int height = viewport[3];
    
    int myDataLength = width * height * 4;
    GLubyte *buffer = (GLubyte *) malloc(myDataLength);
    GLubyte *buffer2 = (GLubyte *) malloc(myDataLength);
    glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
    for(int y1 = 0; y1 < height; y1++) {
        for(int x1 = 0; x1 <width * 4; x1++) {
            buffer2[(height - 1 - y1) * width * 4 + x1] = buffer[y1 * 4 * width + x1];
        }
    }
    free(buffer);
    
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
    int bitsPerComponent = 8;
    int bitsPerPixel = 32;
    int bytesPerRow = 4 * width;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
    CGImageRef imageRef = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, NO, renderingIntent);
    CGColorSpaceRelease(colorSpaceRef);
    CGDataProviderRelease(provider);
    UIImage *image = [ UIImage imageWithCGImage:imageRef scale:s orientation:UIImageOrientationUp ];
    return image;
}

　　

以及颜色判断：

+ (float)colorAtPixel:(CGPoint)point  image:(UIImage *)image
{
    // Cancel if point is outside image coordinates
    if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), point)) {
        return 1000.0;
    }
    NSInteger pointX = trunc(point.x);
    NSInteger pointY = trunc(point.y);
    CGImageRef cgImage = image.CGImage;
    NSUInteger width = image.size.width;
    NSUInteger height = image.size.height;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    int bytesPerPixel = 4;
    int bytesPerRow = bytesPerPixel * 1;
    NSUInteger bitsPerComponent = 8;
    unsigned char pixelData[4] = { 0, 0, 0, 0 };
    CGContextRef context = CGBitmapContextCreate(pixelData,1,1,
                                                 bitsPerComponent,
                                                 bytesPerRow,
                                                 colorSpace,
                                                 kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGColorSpaceRelease(colorSpace);
    CGContextSetBlendMode(context, kCGBlendModeCopy);
    // Draw the pixel we are interested in onto the bitmap context
    CGContextTranslateCTM(context, -pointX, pointY - (CGFloat)height);
    CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage);
    CGContextRelease(context);
    // Convert color values [0..255] to floats [0.0..1.0]
    CGFloat red = (CGFloat)pixelData[0] / 1.0f;
    CGFloat green = (CGFloat)pixelData[1] / 1.0;
    CGFloat blue = (CGFloat)pixelData[2] / 1.0f;
    //    CGFloat alpha = (CGFloat)pixelData[3] / 255.0f;
    //    NSLog(@" colors: RGB  %f %f %f  %f", red, green, blue, alpha);
    return red + green + blue;
}