如何使用CGAffineTransform刻度并同时翻转

Question

我正在尝试使用a转换一个点数组CGAffineTransform.缩放工作完美,但点的左上角为(0,0)而不是左下角.像这样......

通常我会简单地使用,CGAffineTransformMakeScale(1,-1);但因为我已经执行了一个比例,我无法将它添加到现有的转换中.

这是我目前的代码

- (CGAffineTransform)transformFromValueToScreen
{
    CGRect fromRect = self.valueSpace;
    CGRect viewRect = self.screenSpace;

    CGSize scales = CGSizeMake(viewRect.size.width/fromRect.size.width,
                               viewRect.size.height/fromRect.size.height);

    CGAffineTransform transform = CGAffineTransformMakeScale(scales.width, 
                                                             scales.height);

    return transform;
}

Answer 1

我假设fromRect.origin是CGPointZero.

您需要一个复合变换,将原点移动到左下角,翻转Y轴,然后应用所需的缩放.

您可以使用修改变换的函数进行复合变换,如下所示:

- (CGAffineTransform)transformFromValueToScreen {
    CGRect fromRect = self.valueSpace;
    CGRect viewRect = self.screenSpace;

    CGSize scales = CGSizeMake(viewRect.size.width/fromRect.size.width,
                               viewRect.size.height/fromRect.size.height);

    CGAffineTransform transform = CGAffineTransformIdentity;

    // Move origin from upper left to lower left.
    transform = CGAffineTransformTranslate(transform, 0, fromRect.size.height);

    // Flip the sign of the Y axis.
    transform = CGAffineTransformScale(transform, 1, -1);

    // Apply value-to-screen scaling.
    transform = CGAffineTransformScale(transform, scales.width, scales.height);

    return transform;
}