PySide6中的高分屏缩放

切换到PySide6，感觉之前的AA_EnableHighDpiScaling不起作用了

经过一番查询，在官方的github找到了一点说明，Class/Function Deprecations

The High DPI scaling attributes Qt.AA_EnableHighDpiScaling, Qt.AA_DisableHighDpiScaling and Qt.AA_UseHighDpiPixmaps are deprecated. High DPI is by default enabled in Qt 6 and cannot be turned off.

也就是说从6开始，这三个高分屏缩放的API都无了，默认强制开启以及不能关闭，不过问题是并没有感觉到它缩放ORZ

最后在文档中查询到有API是可以调整缩放策略的，搜索HighDpiScaleFactorRoundingPolicy就能找到

• Qt.HighDpiScaleFactorRoundingPolicy.Round 设备像素比0.5及以上的，进行缩放
• Qt.HighDpiScaleFactorRoundingPolicy.Ceil 始终缩放
• Qt.HighDpiScaleFactorRoundingPolicy.Floor 始终不缩放
• Qt.HighDpiScaleFactorRoundingPolicy.RoundPreferFloor 设备像素比0.75及以上的，进行缩放
• Qt.HighDpiScaleFactorRoundingPolicy.PassThrough 不缩放

也许你看完可能还是有些不明白，一开始我也是

然后找到官方widgetgallery.py这个案例，取了部分代码，如下，可以配合这个运行你的GUI，看看各个情况的效果

def format_geometry(rect):
    """Format a geometry as a X11 geometry specification"""
    return "{}x{}{:+d}{:+d}".format(rect.width(), rect.height(), rect.x(), rect.y())


def screen_info(widget):
    """Format information on the screens"""
    policy = QGuiApplication.highDpiScaleFactorRoundingPolicy()
    policy_string = str(policy).split('.')[-1]
    result = "<p>High DPI scale factor rounding policy: {}</p><ol>".format(policy_string)
    for screen in QGuiApplication.screens():
        current = screen == widget.screen()
        result += "<li>"
        if current:
            result += "<i>"
        result += '"{}" {} {}DPI, DPR={}'.format(screen.name(), format_geometry(screen.geometry()), int(screen.logicalDotsPerInchX()), screen.devicePixelRatio())
        if current:
            result += "</i>"
        result += "</li>"
    result += "</ol>"
    return result

用这里得到的结果，显示策略是PassThrough，难怪没感觉到缩放（4K+win10+150%）

<p>High DPI scale factor rounding policy: PassThrough</p><ol><li><i>"\\.\DISPLAY1" 2560x1440+0+0 96DPI, DPR=1.5</i></li></ol>

最终我选择了始终缩放的策略，通过下面的代码即可设定，注意代码应该放到gui界面实例化之前

QGuiApplication.setHighDpiScaleFactorRoundingPolicy(Qt.HighDpiScaleFactorRoundingPolicy.Ceil)