详解如何在pyqt中通过OpenCV实现对窗口的透视变换

窗口的透视变换效果

   当我们点击Win10的UWP应用中的小部件时，会发现小部件会朝着鼠标点击位置凹陷下去，而且不同的点击位置对应着不同的凹陷情况，看起来就好像小部件在屏幕上不只有x轴和y轴，甚至还有一个z轴。要做到这一点，其实只要对窗口进行透视变换即可。下面是对Qt的窗口和按钮进行透视变换的效果：

具体代码

   1.下面先定义一个类，它的作用是将传入的 QPixmap 转换为numpy 数组，然后用 opencv 的 warpPerspective 对数组进行透视变换，最后再将 numpy 数组转为 QPixmap 并返回；

# coding:utf-8

import cv2 as cv
import numpy
from PyQt5.QtGui import QImage, QPixmap

class PixmapPerspectiveTransform:
 """ 透视变换基类 """

 def __init__(self, pixmap=None):
  """ 实例化透视变换对象\n
  Parameter
  ---------
  src : numpy数组 """
  self.pixmap = pixmap

 def setPixmap(self, pixmap: QPixmap):
  """ 设置被变换的QPixmap """
  self.pixmap = QPixmap
  self.src=self.transQPixmapToNdarray(pixmap)
  self.height, self.width = self.src.shape[:2]
  # 变换前后的边角坐标
  self.srcPoints = numpy.float32(
   [[0, 0], [self.width - 1, 0], [0, self.height - 1],
    [self.width - 1, self.height - 1]])

 def setDstPoints(self, leftTop: list, rightTop, leftBottom, rightBottom):
  """ 设置变换后的边角坐标 """
  self.dstPoints = numpy.float32(
   [leftTop, rightTop, leftBottom, rightBottom])

 def getPerspectiveTransform(self, imWidth, imHeight, borderMode=cv.BORDER_CONSTANT, borderValue=[255, 255, 255, 0]) -> QPixmap:
  """ 透视变换图像，返回QPixmap\n
  Parameters
  ----------
  imWidth : 变换后的图像宽度\n
  imHeight : 变换后的图像高度\n
  borderMode : 边框插值方式\n
  borderValue : 边框颜色
  """
  # 如果是jpg需要加上一个透明通道
  if self.src.shape[-1] == 3:
   self.src = cv.cvtColor(self.src, cv.COLOR_BGR2BGRA)
  # 透视变换矩阵
  perspectiveMatrix = cv.getPerspectiveTransform(
   self.srcPoints, self.dstPoints)
  # 执行变换
  self.dst = cv.warpPerspective(self.src, perspectiveMatrix, (
   imWidth, imHeight), borderMode=borderMode, borderValue=borderValue)
  # 将ndarray转换为QPixmap
  return self.transNdarrayToQPixmap(self.dst)

 def transQPixmapToNdarray(self, pixmap: QPixmap):
  """ 将QPixmap转换为numpy数组 """
  width, height = pixmap.width(), pixmap.height()
  channels_count = 4
  image = pixmap.toImage() # type:QImage
  s = image.bits().asstring(height * width * channels_count)
  # 得到BGRA格式数组
  array = numpy.fromstring(s, numpy.uint8).reshape(
   (height, width, channels_count))
  return array

 def transNdarrayToQPixmap(self, array):
  """ 将numpy数组转换为QPixmap """
  height, width, bytesPerComponent = array.shape
  bytesPerLine = 4 * width
  # 默认数组维度为 m*n*4
  dst = cv.cvtColor(array, cv.COLOR_BGRA2RGBA)
  pix = QPixmap.fromImage(
   QImage(dst.data, width, height, bytesPerLine, QImage.Format_RGBA8888))
  return pix

  2.接下来就是这篇博客的主角——PerspectiveWidget，当我们的鼠标单击这个类实例化出来的窗口时，窗口会先通过 self.grab() 被渲染为QPixmap，然后调用 PixmapPerspectiveTransform 中的方法对QPixmap进行透视变换，拿到透视变换的结果后只需隐藏窗口内的小部件并通过 PaintEvent 将结果绘制到窗口上即可。虽然思路很通顺，但是实际操作起来会发现对于透明背景的窗口进行透视变换时，与透明部分交界的部分会被插值上半透明的像素。对于本来就属于深色的像素来说这没什么，但是如果像素是浅色的就会带来很大的视觉干扰，你会发现这些浅色部分旁边被描上了一圈黑边，我们先将这个图像记为img_1。img_1差不多长这个样子，可以很明显看出白色的文字围绕着一圈黑色的描边。

为了解决这个烦人的问题，我又对桌面上的窗口进行截屏，再次透视变换。注意是桌面上看到的窗口，这时的窗口肯定是会有背景的，这时的透视变换就不会存在上述问题，记这个透视变换完的图像为img_2。但实际上我们本来是不想要img_2中的背景的，所以只要将img_2中的背景替换完img_1中的透明背景，下面是具体代码：

# coding:utf-8

import numpy as np

from PyQt5.QtCore import QPoint, Qt
from PyQt5.QtGui import QPainter, QPixmap, QScreen, QImage
from PyQt5.QtWidgets import QApplication, QWidget

from my_functions.get_pressed_pos import getPressedPos
from my_functions.perspective_transform_cv import PixmapPerspectiveTransform

class PerspectiveWidget(QWidget):
 """ 可进行透视变换的窗口 """

 def __init__(self, parent=None, isTransScreenshot=False):
  super().__init__(parent)
  self.__visibleChildren = []
  self.__isTransScreenshot = isTransScreenshot
  self.__perspectiveTrans = PixmapPerspectiveTransform()
  self.__screenshotPix = None
  self.__pressedPix = None
  self.__pressedPos = None

 @property
 def pressedPos(self) -> str:
  """ 返回鼠标点击位置 """
  return self.__pressedPos

 def mousePressEvent(self, e):
  """ 鼠标点击窗口时进行透视变换 """
  super().mousePressEvent(e)
  self.grabMouse()
  pixmap = self.grab()
  self.__perspectiveTrans.setPixmap(pixmap)
  # 根据鼠标点击位置的不同设置背景封面的透视变换
  self.__setDstPointsByPressedPos(getPressedPos(self,e))
  # 获取透视变换后的QPixmap
  self.__pressedPix = self.__getTransformPixmap()
  # 对桌面上的窗口进行截图
  if self.__isTransScreenshot:
   self.__adjustTransformPix()
  # 隐藏本来看得见的小部件
  self.__visibleChildren = [
   child for child in self.children() if hasattr(child, 'isVisible') and child.isVisible()]
  for child in self.__visibleChildren:
   if hasattr(child, 'hide'):
    child.hide()
  self.update()

 def mouseReleaseEvent(self, e):
  """ 鼠标松开时显示小部件 """
  super().mouseReleaseEvent(e)
  self.releaseMouse()
  self.__pressedPos = None
  self.update()
  # 显示小部件
  for child in self.__visibleChildren:
   if hasattr(child, 'show'):
    child.show()

 def paintEvent(self, e):
  """ 绘制背景 """
  super().paintEvent(e)
  painter = QPainter(self)
  painter.setRenderHints(QPainter.Antialiasing | QPainter.HighQualityAntialiasing |
        QPainter.SmoothPixmapTransform)
  painter.setPen(Qt.NoPen)
  # 绘制背景图片
  if self.__pressedPos:
   painter.drawPixmap(self.rect(), self.__pressedPix)

 def __setDstPointsByPressedPos(self,pressedPos:str):
  """ 通过鼠标点击位置设置透视变换的四个边角坐标 """
  self.__pressedPos = pressedPos
  if self.__pressedPos == 'left':
   self.__perspectiveTrans.setDstPoints(
    [5, 4], [self.__perspectiveTrans.width - 2, 1],
    [3, self.__perspectiveTrans.height - 3],
    [self.__perspectiveTrans.width - 2, self.__perspectiveTrans.height - 1])
  elif self.__pressedPos == 'left-top':
   self.__perspectiveTrans.setDstPoints(
    [6, 5], [self.__perspectiveTrans.width - 1, 1],
    [1, self.__perspectiveTrans.height - 2],
    [self.__perspectiveTrans.width - 2, self.__perspectiveTrans.height - 1])
  elif self.__pressedPos == 'left-bottom':
   self.__perspectiveTrans.setDstPoints(
    [2, 3], [self.__perspectiveTrans.width - 3, 0],
    [4, self.__perspectiveTrans.height - 4],
    [self.__perspectiveTrans.width - 2, self.__perspectiveTrans.height - 2])
  elif self.__pressedPos == 'top':
   self.__perspectiveTrans.setDstPoints(
    [3, 5], [self.__perspectiveTrans.width - 4, 5],
    [1, self.__perspectiveTrans.height - 2],
    [self.__perspectiveTrans.width - 2, self.__perspectiveTrans.height - 2])
  elif self.__pressedPos == 'center':
   self.__perspectiveTrans.setDstPoints(
    [3, 4], [self.__perspectiveTrans.width - 4, 4],
    [3, self.__perspectiveTrans.height - 3],
    [self.__perspectiveTrans.width - 4, self.__perspectiveTrans.height - 3])
  elif self.__pressedPos == 'bottom':
   self.__perspectiveTrans.setDstPoints(
    [2, 2], [self.__perspectiveTrans.width - 3, 3],
    [3, self.__perspectiveTrans.height - 3],
    [self.__perspectiveTrans.width - 4, self.__perspectiveTrans.height - 3])
  elif self.__pressedPos == 'right-bottom':
   self.__perspectiveTrans.setDstPoints(
    [1, 0], [self.__perspectiveTrans.width - 3, 2],
    [1, self.__perspectiveTrans.height - 2],
    [self.__perspectiveTrans.width - 5, self.__perspectiveTrans.height - 4])
  elif self.__pressedPos == 'right-top':
   self.__perspectiveTrans.setDstPoints(
    [0, 1], [self.__perspectiveTrans.width - 7, 5],
    [2, self.__perspectiveTrans.height - 1],
    [self.__perspectiveTrans.width - 2, self.__perspectiveTrans.height - 2])
  elif self.__pressedPos == 'right':
   self.__perspectiveTrans.setDstPoints(
    [1, 1], [self.__perspectiveTrans.width - 6, 4],
    [2, self.__perspectiveTrans.height - 1],
    [self.__perspectiveTrans.width - 4, self.__perspectiveTrans.height - 3])

 def __getTransformPixmap(self) -> QPixmap:
  """ 获取透视变换后的QPixmap """
  pix = self.__perspectiveTrans.getPerspectiveTransform(
   self.__perspectiveTrans.width, self.__perspectiveTrans.height).scaled(
    self.size(), Qt.KeepAspectRatio, Qt.SmoothTransformation)
  return pix

 def __getScreenShot(self) -> QPixmap:
  """ 对窗口口所在的桌面区域进行截图 """
  screen = QApplication.primaryScreen() # type:QScreen
  pos = self.mapToGlobal(QPoint(0, 0)) # type:QPoint
  pix = screen.grabWindow(
   0, pos.x(), pos.y(), self.width(), self.height())
  return pix

 def __adjustTransformPix(self):
  """ 对窗口截图再次进行透视变换并将两张图融合，消除可能存在的黑边 """
  self.__screenshotPix = self.__getScreenShot()
  self.__perspectiveTrans.setPixmap(self.__screenshotPix)
  self.__screenshotPressedPix = self.__getTransformPixmap()
  # 融合两张透视图
  img_1 = self.__perspectiveTrans.transQPixmapToNdarray(self.__pressedPix)
  img_2 = self.__perspectiveTrans.transQPixmapToNdarray(self.__screenshotPressedPix)
  # 去除非透明背景部分
  mask = img_1[:, :, -1] == 0
  img_2[mask] = img_1[mask]
  self.__pressedPix = self.__perspectiveTrans.transNdarrayToQPixmap(img_2)

在mousePressEvent中调用了一个全局函数 getPressedPos(widget,e) ，如果将窗口分为九宫格，它就是用来获取判断鼠标的点击位置落在九宫格的哪个格子的，因为我在其他地方有用到它，所以没将其设置为PerspectiveWidget的方法成员。下面是这个函数的代码：

# coding:utf-8

from PyQt5.QtGui import QMouseEvent

def getPressedPos(widget, e: QMouseEvent) -> str:
 """ 检测鼠标并返回按下的方位 """
 pressedPos = None
 width = widget.width()
 height = widget.height()
 leftX = 0 <= e.x() <= int(width / 3)
 midX = int(width / 3) < e.x() <= int(width * 2 / 3)
 rightX = int(width * 2 / 3) < e.x() <= width
 topY = 0 <= e.y() <= int(height / 3)
 midY = int(height / 3) < e.y() <= int(height * 2 / 3)
 bottomY = int(height * 2 / 3) < e.y() <= height
 # 获取点击位置
 if leftX and topY:
  pressedPos = 'left-top'
 elif midX and topY:
  pressedPos = 'top'
 elif rightX and topY:
  pressedPos = 'right-top'
 elif leftX and midY:
  pressedPos = 'left'
 elif midX and midY:
  pressedPos = 'center'
 elif rightX and midY:
  pressedPos = 'right'
 elif leftX and bottomY:
  pressedPos = 'left-bottom'
 elif midX and bottomY:
  pressedPos = 'bottom'
 elif rightX and bottomY:
  pressedPos = 'right-bottom'
 return pressedPos

使用方法

   很简单，只要将代码中的QWidget替换为PerspectiveWidget就可以享受透视变换带来的无尽乐趣。要想向gif中那样对按钮也进行透视变换，只要按代码中所做的那样重写mousePressEvent、mouseReleaseEvent 和 paintEvent 即可，如果有对按钮使用qss，记得在paintEvent中加上super().paintEvent(e)，这样样式表才会起作用。总之框架已经给出，具体操作取决于你。如果你喜欢这篇博客的话，记得点个赞哦(oﾟ▽ﾟ)o 。顺便做个下期预告：在gif中可以看到界面切换时带了弹入弹出的动画，在下一篇博客中我会对如何实现QStackedWidget的界面切换动画进行介绍，敬请期待~~

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