Question

我试图在iOS设备上以编程方式获取单个像素的RGBA颜色。我目前有一个方法，但它涉及截取整个屏幕的截图，然后找到中心像素的RGB颜色，因为我想在游戏的每个时间步找到中心像素，这会导致性能的大幅滞后生成屏幕截图时的应用程序出于这个原因，我想截取屏幕上只有一个像素的屏幕截图，但无法在网上找到任何方法...这是我目前的方法：

UIImage *screenImage = [self screenshot];

CGPoint pointToCheck = CGPointMake(0.5 , 0.5);

UIColor *color = [self colorFromImage:screenImage sampledAtPoint:pointToCheck];

- (UIColor*)colorFromImage:(UIImage*)image sampledAtPoint:(CGPoint)p {
    CGImageRef cgImage = [image CGImage];
    CGDataProviderRef provider = CGImageGetDataProvider(cgImage);
    CFDataRef bitmapData = CGDataProviderCopyData(provider);
    const UInt8* data = CFDataGetBytePtr(bitmapData);
    size_t bytesPerRow = CGImageGetBytesPerRow(cgImage);
    size_t width = CGImageGetWidth(cgImage);
    size_t height = CGImageGetHeight(cgImage);
    int col = p.x*(width-1);
    int row = p.y*(height-1);
    const UInt8* pixel = data + row*bytesPerRow+col*4;
    UIColor* returnColor = [UIColor colorWithRed:pixel[0]/255. green:pixel[1]/255. blue:pixel[2]/255. alpha:1.0];
    CFRelease(bitmapData);
    return returnColor;
}

- (UIImage *) screenshot
{
    CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    else
        UIGraphicsBeginImageContext(imageSize);

    CGContextRef context = UIGraphicsGetCurrentContext();

    // Iterate over every window from back to front
    for (UIWindow *window in [[UIApplication sharedApplication] windows])
    {
        if (![window respondsToSelector:@selector(screen)] || [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;
}

Answer 1

按照此处的代码获取单个像素的颜色：

iOS -- detect the color of a pixel?

希望有所帮助：）

iOS编程单像素截图

1 个答案: