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Commit 6319140b authored by Michael Droettboom's avatar Michael Droettboom
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Add documentation to wasm_backend.py

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src/wasm_backend.py
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"""
A matplotlib backend that renders to an HTML5 canvas in the same thread.
The Agg backend is used for the actual rendering underneath, and renders the
buffer to the HTML5 canvas. This happens with only a single copy of the data
into the Canvas -- passing the data from Python to Javascript requires no
copies.
See matplotlib.backend_bases for documentation for most of the methods, since
this primarily is just overriding methods in the base class.
"""
# TODO: Figure resizing support
import base64
import io
import math
......@@ -6,75 +20,11 @@ from matplotlib.backends import backend_agg
from matplotlib.backend_bases import _Backend
from matplotlib import backend_bases, _png
from js import iodide
from js import document
from js import window
from js import ImageData
# http://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes
_SHIFT_LUT = {
59: ':',
61: '+',
173: '_',
186: ':',
187: '+',
188: '<',
189: '_',
190: '>',
191: '?',
192: '~',
219: '{',
220: '|',
221: '}',
222: '"'
}
_LUT = {
8: 'backspace',
9: 'tab',
13: 'enter',
16: 'shift',
17: 'control',
18: 'alt',
19: 'pause',
20: 'caps',
27: 'escape',
32: ' ',
33: 'pageup',
34: 'pagedown',
35: 'end',
36: 'home',
37: 'left',
38: 'up',
39: 'right',
40: 'down',
45: 'insert',
46: 'delete',
91: 'super',
92: 'super',
93: 'select',
106: '*',
107: '+',
109: '-',
110: '.',
111: '/',
144: 'num_lock',
145: 'scroll_lock',
186: ':',
187: '=',
188: ',',
189: '-',
190: '.',
191: '/',
192: '`',
219: '[',
220: '\\',
221: ']',
222: "'"
}
class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
supports_blit = False
......@@ -87,12 +37,21 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
self._ratio = 1
def get_element(self, name):
"""
Looks up an HTMLElement created for this figure.
"""
# TODO: Should we store a reference here instead of always looking it
# up? I'm a little concerned about weird Python/JS
# cross-memory-management issues...
return document.getElementById(self._id + name)
def get_dpi_ratio(self, context):
"""
Gets the ratio of physical pixels to logical pixels for the given HTML
Canvas context.
This is typically 2 on a HiDPI ("Retina") display, and 1 otherwise.
"""
backing_store = (
context.backingStorePixelRatio or
context.webkitBackingStorePixel or
......@@ -104,36 +63,52 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
)
return (window.devicePixelRatio or 1) / backing_store
def create_root_element(self):
# Designed to be overridden by subclasses for use in contexts other
# than iodide.
from js import iodide
return iodide.output.element('div')
def show(self):
# If we've already shown this canvas elsewhere, don't create a new one,
# just reuse it and scroll to the existing one.
existing = self.get_element('')
if existing is not None:
self.draw_idle()
existing.scrollIntoView()
return
# Disable the right-click context menu.
# Doesn't work in all browsers.
def ignore(event):
event.preventDefault()
return False
window.addEventListener('contextmenu', ignore)
# Create the main canvas and determine the physical to logical pixel
# ratio
canvas = document.createElement('canvas')
context = canvas.getContext('2d')
self._ratio = self.get_dpi_ratio(context)
if self._ratio != 1:
self.figure.dpi *= self._ratio
renderer = self.get_renderer()
width, height = self.get_width_height()
div = iodide.output.element('div')
div = self.create_root_element()
div.setAttribute('style', 'width: {}px'.format(width / self._ratio))
div.id = self._id
# The top bar
top = document.createElement('div')
top.id = self._id + 'top'
top.setAttribute('style', 'font-weight: bold; text-align: center')
top.textContent = self._title
div.appendChild(top)
# A div containing two canvases stacked on top of one another:
# - The bottom for rendering matplotlib content
# - The top for rendering interactive elements, such as the zoom
# rubberband
canvas_div = document.createElement('div')
canvas_div.setAttribute('style', 'position: relative')
......@@ -156,7 +131,10 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
'width: {}px; height: {}px'.format(
width / self._ratio, height / self._ratio)
)
# Canvas must have a "tabindex" attr in order to receive keyboard events
rubberband.setAttribute('tabindex', '0')
# Event handlers are added to the canvas "on top", even though most of the
# activity happens in the canvas below.
rubberband.addEventListener('click', self.onclick)
rubberband.addEventListener('mousemove', self.onmousemove)
rubberband.addEventListener('mouseup', self.onmouseup)
......@@ -172,6 +150,7 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
div.appendChild(canvas_div)
# The bottom bar, with toolbar and message display
bottom = document.createElement('div')
toolbar = self.toolbar.get_element()
bottom.appendChild(toolbar)
......@@ -184,7 +163,9 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
self.draw()
def draw(self):
# Render the figure using Agg
super().draw()
# Copy the image buffer to the canvas
width, height = self.get_width_height()
canvas = self.get_element('canvas')
image_data = ImageData.new(
......@@ -209,6 +190,7 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
x = (event.offsetX * self._ratio)
y = ((height / self._ratio) - event.offsetY) * self._ratio
button = event.button + 1
# Disable the right-click context menu in some browsers
if button == 3:
event.preventDefault()
event.stopPropagation()
......@@ -234,10 +216,12 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
def onmouseenter(self, event):
window.addEventListener('contextmenu', ignore)
# When the mouse is over the figure, get keyboard focus
self.get_element('rubberband').focus()
self.enter_notify_event(guiEvent=event)
def onmouseleave(self, event):
# When the mouse leaves the figure, drop keyboard focus
self.get_element('rubberband').blur()
self.leave_notify_event(guiEvent=event)
......@@ -255,12 +239,75 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
def set_cursor(self, cursor):
self.get_element('rubberband').style.cursor = self._cursor_map.get(cursor, 0)
# http://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes
_SHIFT_LUT = {
59: ':',
61: '+',
173: '_',
186: ':',
187: '+',
188: '<',
189: '_',
190: '>',
191: '?',
192: '~',
219: '{',
220: '|',
221: '}',
222: '"'
}
_LUT = {
8: 'backspace',
9: 'tab',
13: 'enter',
16: 'shift',
17: 'control',
18: 'alt',
19: 'pause',
20: 'caps',
27: 'escape',
32: ' ',
33: 'pageup',
34: 'pagedown',
35: 'end',
36: 'home',
37: 'left',
38: 'up',
39: 'right',
40: 'down',
45: 'insert',
46: 'delete',
91: 'super',
92: 'super',
93: 'select',
106: '*',
107: '+',
109: '-',
110: '.',
111: '/',
144: 'num_lock',
145: 'scroll_lock',
186: ':',
187: '=',
188: ',',
189: '-',
190: '.',
191: '/',
192: '`',
219: '[',
220: '\\',
221: ']',
222: "'"
}
def _convert_key_event(self, event):
code = int(event.which)
value = chr(code)
shift = event.shiftKey and code != 16
ctrl = event.ctrlKey and code != 17
alt = event.altKey and code != 18
# letter keys
if 65 <= code <= 90:
if not shift:
......@@ -279,11 +326,11 @@ class FigureCanvasWasm(backend_agg.FigureCanvasAgg):
elif 96 <= code <= 105:
value = '%s' % (code - 96)
# keys with shift alternatives
elif code in _SHIFT_LUT and shift:
value = _SHIFT_LUT[code]
elif code in self._SHIFT_LUT and shift:
value = self._SHIFT_LUT[code]
shift = False
elif code in _LUT:
value = _LUT[code]
elif code in self._LUT:
value = self._LUT[code]
key = []
if shift:
......@@ -371,6 +418,7 @@ class NavigationToolbar2Wasm(backend_bases.NavigationToolbar2):
pass
def get_element(self):
# Creat the HTML content for the toolbar
div = document.createElement('span')
def add_spacer():
......@@ -405,6 +453,9 @@ class NavigationToolbar2Wasm(backend_bases.NavigationToolbar2):
self.download(format, FILE_TYPES[format])
def download(self, format, mimetype):
# Creates a temporary `a` element with a URL containing the image
# content, and then virtually clicks it. Kind of magical, but it
# works...
element = document.createElement('a')
data = io.BytesIO()
try:
......
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