我使用以下功能允许应用用户在其画布照片上插入文字。当文本接近边缘时，它的工作正如预期的那样缩小，但如果文本不大于画布，我无法弄清楚如何使文本居中。
var canvas4 = document.getElementById("canvas4");
var ctx4 = canvas4.getContext("2d");
canvas4.width = $(window).width();
canvas4.height = $(window).height();
var txt = value,
tw,
oc, octx;
ctx4.font = '40px sans-serif';
ctx4.fillStyle = 'blue';
ctx4.textBaseline = 'top';
ctx4.globalAlpha = 0.50;
tw = ctx4.measureText(txt).width;
if (tw > canvas4.width - 20) {
oc = document.createElement('canvas');
octx = oc.getContext('2d');
oc.width = tw;
oc.height = parseInt(ctx4.font, 10) * 1.2;
octx.font = '40px sans-serif';
octx.textBaseline = 'top';
octx.fillText(txt, 0, 0);
ctx4.drawImage(oc, 10, canvas4.height - 100, canvas4.width - 20, (canvas4.width - 20) / tw * oc.height);
} else {
ctx4.fillText(txt, 10, canvas4.height - 100);
};
我尝试过文字对齐，例如
ctx4.textAlign = 'center, canvas4.width / 2, canvas4.height - 100';
答案 0 :(得分：1)
import requests
import os
from Tkinter import Label, Frame, Tk, BOTH, TOP, LEFT, X, Button, Entry, FLAT, StringVar, DISABLED
from ttk import Progressbar
import tkFont
import tkMessageBox
class Downloader:
def __init__(self,parent):
self.parent = parent
self.parent.title("downloader")
self.parent_frame = Frame(self.parent)
self.parent_frame.pack(fill=BOTH,expand=True) # expands fill all remining spaces
self.control_button_frame=Frame(self.parent_frame)
self.control_button_frame.pack(side=TOP,fill=X)
self.downloading_url=StringVar()
self.downloading_url.set("paste downloadable url here (use ctrl + v)") # make a Tkinter StringVar between root = Tk() window
self.req_obj = None
self.source_file_size = None
self.error_msg = None
self.downloaded_file_size = 0
self.pause_flag = 0
self.cancel_flag = 0
self.AddContainers()
self.AddWidgets()
def AddContainers(self):
self.top_frame = Frame(self.parent_frame)
self.top_frame.pack(side=TOP,pady=10,padx=10,fill=X)
self.downloads_details_frame=Frame(self.parent_frame)
self.downloads_details_frame.pack(side=TOP,padx=10,fill=X)
self.status_history_buttons_frame=Frame(self.downloads_details_frame)
self.status_history_buttons_frame.pack(side=TOP,fill=X)
self.downloads_status_show_frame=Frame(self.downloads_details_frame,bg="white")
self.downloads_status_show_frame.pack(side=TOP,fill=X)
self.downloads_status_show_left_frame = Frame(self.downloads_status_show_frame)
self.downloads_status_show_left_frame.pack(side=LEFT, fill=X)
self.downloads_status_show_right_frame = Frame(self.downloads_status_show_frame)
self.downloads_status_show_right_frame.pack(side=LEFT, fill=X)
self.progress_bar_frame = Frame(self.parent_frame)
self.progress_bar_frame.pack(side=TOP,fill=X)
self.control_button_frame=Frame(self.parent_frame)
self.control_button_frame.pack(side=TOP,fill=X)
def AddWidgets(self):
label_names = ["Status","File size","Downloaded","Transfer rate","Time left","Resume Capability"]
self.downloading_status_data_label = {}
address_label = Label(self.top_frame, text ="Address")
address_label.pack(side="left")
self.url_font_style = tkFont.Font(family = 'ms sans Serif', size = 9, weight = "normal" )
self.url_entry_field = Entry(self.top_frame,width=60,font = self.url_font_style,textvariable=self.downloading_url)
self.url_entry_field.pack(side="left",padx=5,fill=X,expand=True)
self.url_ok_button = Button(self.top_frame, text ="Download", width = 8, command = self.UrlProcessing)
self.url_ok_button.pack(side="left")
self.status_button = Button(self.status_history_buttons_frame,text="Download Status",relief=FLAT,bg="white",anchor="w", width=13)
self.status_button.pack(side="left")
self.show_history_button=Button(self.status_history_buttons_frame,text="History")
self.show_history_button.pack(side="left")
for names in label_names:
lab = Label(self.downloads_status_show_left_frame, text=names, anchor="w",bg="white", width=16)
lab.pack(side=TOP,fill=X)
self.status_data_label = Label(self.downloads_status_show_right_frame, text = "N/A", anchor="w",bg="white")
self.status_data_label.pack(side=TOP,fill=X)
self.file_size_data_label = Label(self.downloads_status_show_right_frame, text = "N/A", anchor="w",bg="white")
self.file_size_data_label.pack(side=TOP,fill=X)
self.downloaded_data_label = Label(self.downloads_status_show_right_frame, text = "N/A", anchor="w",bg="white")
self.downloaded_data_label.pack(side=TOP,fill=X)
self.transfer_rate_data_label = Label(self.downloads_status_show_right_frame, text = "N/A", anchor="w",bg="white")
self.transfer_rate_data_label.pack(side=TOP,fill=X)
self.time_left_data_label = Label(self.downloads_status_show_right_frame, text = "N/A", anchor="w",bg="white")
self.time_left_data_label.pack(side=TOP,fill=X)
self.resume_status_data_label = Label(self.downloads_status_show_right_frame, text = "N/A", anchor="w",bg="white")
self.resume_status_data_label.pack(side=TOP,fill=X)
self.progress=Progressbar(self.progress_bar_frame,orient="horizontal",length=200,mode="determinate")
self.progress.pack(fill=X,side="left",expand=True)
self.progress["value"] = 0
self.cancel_button=Button(self.control_button_frame,text="cancel",width=8, command = self.CancelDownload)
self.cancel_button.pack(side="right",padx=10,pady=5)
self.start_pause_button=Button(self.control_button_frame,text="pause",width=8, command = self.StartPause)
self.start_pause_button.pack(side="right",padx=10,pady=5)
def ErrorMessageHandler(self,err_message):
tkMessageBox.showerror("Error",err_message)
def ShowMessage(self,title,message):
tkMessageBox.showinfo(title,message)
def UpdateDownloadingDetails(self,meta_data):
self.status_data_label.config(text=meta_data["Status"])
self.file_size_data_label.config(text=meta_data["File size"])
self.downloaded_data_label.config(text=meta_data["Downloaded"])
self.transfer_rate_data_label.config(text=meta_data["Transfer rate"])
self.time_left_data_label.config(text=meta_data["Time left"])
self.parent.update()
def CancelDownload(self):
self.cancel_flag = 1
def StartPause(self):
if self.pause_flag == 0:
self.start_pause_button.config(text ="start")
self.parent.update()
self.pause_flag = 1
else:
self.start_pause_button.config(text ="pause")
self.parent.update()
self.pause_flag = 0
self.UrlProcessing()
def MakeRequest(self,source_url):
start_byte_pos = 0
start_header = {'Range': 'bytes=%d-' % start_byte_pos}
try:
self.req_obj = requests.get(source_url, headers=start_header, stream = True)
if self.req_obj.status_code == 206:
self.source_file_size = int(self.req_obj.headers['Content-Length'])
self.progress["maximum"] = self.source_file_size
return True
except HTTPError, e:
self.error_msg = 'HTTPError = ' + str(e.code)
return False
except URLError, e:
self.error_msg = 'URLError = ' + str(e.reason)
return False
except httplib.HTTPException, e:
self.error_msg = 'HTTPException'
return False
except Exception:
self.error_msg = 'generic exception: ' + "Unknown Url Type" #traceback.format_exc()
return False
def GetSizeInFormat(self, total_bytes):
formatted_size = None
if total_bytes < 1024:
formatted_size= str(total_bytes)+" Bytes"
elif total_bytes < 1048576:
formatted_size = str(float(total_bytes/1024))+" KB"
if (total_bytes % 1024) >= 8:
formatted_size = str(total_bytes/1024) + "."+str(int ( (total_bytes % 1024 ) / 8)) + " KB"
elif total_bytes < 1073741824:
formatted_size = str(float(total_bytes/1048576))+" MB"
if (total_bytes % 1048576) >= 1024:
formatted_size = str(total_bytes/1048576) + "."+str(int ( (total_bytes % 1048576 ) / 1024)) + " MB"
elif total_bytes >= 1073741824:
formatted_size = str(float(total_bytes/1073741824))+" GB"
if (total_bytes % 1073741824) >= 1048576:
formatted_size = str(total_bytes/1073741824) + "."+str(int ( (total_bytes % 1073741824 ) / 1048576)) + " GB"
return formatted_size
def GetTimeInFormat(self, total_seconds):
formatted_time = None
if total_seconds >= 3600:
formatted_time = str(total_seconds/3600)+" hr"
if (total_seconds % 3600) >= 60:
formatted_time = formatted_time+" "+str( (total_seconds % 3600) / 60)+" min"
elif (total_seconds % 3600) < 60 and (total_seconds % 3600) > 0:
formatted_time = formatted_time +" "+str(total_seconds%3600)+" sec"
elif total_seconds >= 60:
formatted_time = str(total_seconds / 60)+" min"
if (total_seconds % 60) >0:
formatted_time = formatted_time+" "+str(total_seconds % 60)+" sec"
else:
formatted_time = str(total_seconds)+" sec"
return formatted_time
def GetFileName(self,source_url):
file_name = None
temp = source_url.split('/')[-1]
for raw_data in ['<','>',':','"','/','|','?','*']:
if raw_data in temp:
temp = temp.replace(raw_data,'_')
file_name = temp
return file_name
def CheckFileExistence(self,file_name):
if os.path.exists(file_name):
return True
else:
return False
def GetLocalFileSize(self,file_name):
return os.path.getsize(file_name)
def SetResumeDownload(self,fileurl, resume_byte_pos):
resume_header = {'Range': 'bytes=%d-' % resume_byte_pos}
return requests.get(fileurl, headers=resume_header, stream=True)
def DownloadFile(self,file_ptr):
chunk_size = (1024*1024)
self.status_data_label.config(text="downloading")
self.file_size_data_label.config(text=self.GetSizeInFormat(self.source_file_size))
self.downloaded_data_label.config(text=self.GetSizeInFormat(self.downloaded_file_size))
self.transfer_rate_data_label.config(text = self.GetSizeInFormat(1024*1024))
temp = (self.source_file_size-self.downloaded_file_size)/chunk_size
self.time_left_data_label.config(text= self.GetTimeInFormat(temp))
self.resume_status_data_label.config(text="yes", fg="blue")
self.parent.update()
for chunk in self.req_obj.iter_content(chunk_size):
self.parent.update()
if chunk:
self.downloaded_file_size = self.downloaded_file_size + len(chunk)
file_ptr.write(chunk)
self.downloaded_data_label.config(text=self.GetSizeInFormat(self.downloaded_file_size))
temp = (self.source_file_size-self.downloaded_file_size)/chunk_size
self.time_left_data_label.config(text= self.GetTimeInFormat(temp))
self.progress["value"] = self.downloaded_file_size
self.parent.update()
if self.pause_flag == 1:
self.req_obj.close()
break
if self.cancel_flag ==1:
file_ptr.flush()
file_ptr.close()
self.req_obj.close()
self.parent.destroy()
def UrlProcessing(self):
self.url_ok_button.config(state=DISABLED)
self.parent.update()
self.url = self.downloading_url.get()
file_name = self.GetFileName(self.url)
if self.CheckFileExistence(file_name):
if self.MakeRequest(self.url):
temp_file_size = self.GetLocalFileSize(file_name)
if temp_file_size == self.source_file_size:
self.ShowMessage(file_name,"File is already downloaded")
else:
self.status_data_label.config(text = "connecting",fg="blue")
self.parent.update()
self.req_obj.close()
self.req_obj = self.SetResumeDownload(self.url,temp_file_size)
file_ptr = open(file_name, 'ab')
self.DownloadFile(file_ptr)
file_ptr.flush()
file_ptr.close()
self.req_obj.close()
if self.source_file_size == self.downloaded_file_size:
self.ShowMessage(file_name,"Downloading Completed")
self.parent.destroy()
else:
self.ErrorMessageHandler(self.error_msg)
else:
self.status_data_label.config(text = "connecting",fg="blue")
self.parent.update()
if self.MakeRequest(self.url):
file_ptr = open(file_name, 'wb')
self.DownloadFile(file_ptr)
file_ptr.flush()
file_ptr.close()
self.req_obj.close()
if self.source_file_size == self.downloaded_file_size:
self.ShowMessage(file_name,"Downloading Completed")
self.parent.destroy()
else:
self.ErrorMessageHandler(self.error_msg)
if __name__=='__main__' :
root = Tk()
app = Downloader(root)
root.mainloop()
我没有使用canvas元素的经验。但这会对你有所帮助。
答案 1 :(得分：0)
textAlign只需一个字"center"。剩下的就在你的fillText电话中。
ctx4.textAlign = 'center';
ctx4.fillText(txt, canvas4.width / 2, canvas4.height - 100);
将textAlign设置为"center"会使文本的中心显示在fillText调用中指定的位置。如果该点在画布上居中，则整个文本将在画布上居中。