wxPython之wx.DC

wx.DC

　　能够在电脑显示器上显示对象，是GUI工具包最基本的功能之一。对于wxPython，对象通过发送给设备上下文（Device Context， DC）的绘制命令显示在屏幕上。在底层，所有控件都是以位图形式绘制在屏幕上。DC的接口允许自定义控件的外观。
　　所有可见地显示在屏幕上的窗口发出一些绘制命令给DC，告诉系统哪些像素信息显示在屏幕上。一些控件类，例如wx.Control， wx.Window和wx.Panel，允许通过使用wx.EVT_PAINT，自定义控件在屏幕上显示什么。

示例说明

创建一个滑动显示窗口部件，用来显示目录下PNG或JPG文件。

#-*-coding: UTF-8 -*-#------------------------------------------------------#Purpose: nothing....#Author: 阿Bin先生#Created: 2017年5月21日#------------------------------------------------------import osimport wxclass SlideShowPanel(wx.PyPanel):    def __init__(self, parent):        super(SlideShowPanel, self).__init__(parent)        # Attributes        self.idx = 0 # Current index in image list        self.images = list() # list of images found to display        # Event Handlers        self.Bind(wx.EVT_PAINT, self.OnPaint)        self.Bind(wx.EVT_LEFT_UP, self.Next)        self.Bind(wx.EVT_RIGHT_UP, self.Previous)        self.SetImageDir("E:/TestData")    def DoGetBestSize(self):        """Virtual override for PyPanel"""        newsize = wx.Size(0, 0)        if len(self.images):            imgpath = self.images[self.idx]            bmp = wx.Bitmap(imgpath)            newsize = bmp.GetSize()            newsize = newsize + (20, 20) # some padding        else:            tsize = self.GetTextExtent("No Image!")            newsize = tsize + (20, 20)            # Ensure new size is at least 300x300            return wx.Size(max(300, newsize[0]),            max(300, newsize[1]))    def OnPaint(self, event):        """Draw the image on to the panel"""        dc = wx.PaintDC(self) # Must create a PaintDC        # Get the working rectangle        rect = self.GetClientRect()        # Setup the DC        dc.SetTextForeground(wx.BLACK)        # Do the drawing        if len(self.images):            # Draw the current image            imgpath = self.images[self.idx]            bmp = wx.Bitmap(imgpath)            bsize = bmp.GetSize()            # Try and center the image            # Note: assumes image is smaller than canvas            xpos = (rect.width - bsize[0]) / 2            ypos = (rect.height - bsize[1]) / 2            dc.DrawBitmap(bmp, xpos, ypos)            # Draw a label under the image saying what            # number in the set it is.            imgcount = len(self.images)            number = "%d / %d" % (self.idx+1, imgcount)            tsize = dc.GetTextExtent(number)            xpos = (rect.width - tsize[0]) / 2            ypos = ypos + bsize[1] + 5 # 5px below image            dc.DrawText(number, xpos, ypos)        else:            # Display that there are no images            font = self.GetFont()            font.SetWeight(wx.FONTWEIGHT_BOLD)            dc.SetFont(font)            dc.DrawLabel("No Images!", rect, wx.ALIGN_CENTER)    def Next(self, event):        """Goto next image"""        self.idx += 1        if self.idx >= len(self.images):            self.idx = 0 # Go back to zero        self.Refresh() # Causes a repaint    def Previous(self, event):        """Goto previous image"""        self.idx -= 1        if self.idx < 0:            self.idx = len(self.images) - 1 # Goto end        self.Refresh() # Causes a repaint    def SetImageDir(self, imgpath):        """Set the path to where the images are"""        assert os.path.exists(imgpath)        # Find all the images in the directory        self.images = [ os.path.join(imgpath, img)                for img in os.listdir(imgpath)                if img.lower().endswith('.png') or                img.lower().endswith('.jpg') ]        self.idx = 0class MyFrame(wx.Frame):    def __init__(self, parent, *args, **kwargs):        super(MyFrame, self).__init__(parent, *args, **kwargs)        # Attributes        self.mypanel = SlideShowPanel(self)        self.mypanel.SetBackgroundColour(wx.WHITE)class MyApp(wx.App):    def OnInit(self):        self.frame = MyFrame(None, title="wx.DC",size = [1000, 900])        self.SetTopWindow(self.frame)        self.frame.Show()        return Trueif __name__ == "__main__":    app = MyApp(False)    app.MainLoop()

运行结果：

示例分析

　　SlideShowPanel继承于PyPanel，以至于能够访问它的一些虚方法。DoGetBestSize方法是虚重写。绑定绘制处理器给EVT_PAINT事件。鼠标左击向前预览，鼠标右击向后预览。Refresh方法导致系统发出EVT_PAINT事件。
　　　OnPaint方法，首先实例一个PaintDC对象，PaintDC提供了DC的接口，允许绘制外观在屏幕上。GetClientRect获取控件的客户端区域。DC的DrawBitmap方法绘制图片对象到屏幕上，DC的DrawLabel方法绘制文本。