MultiMedia

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PictureBox: Drawing, text, images, sprites

The PictureBox control is a powerful container for images, drawing and text.

  • Before you can output anything to a PictureBox, a context must be created:
pb = PictureBox1.getContext("2d")
  • All drawing, images, etc. are done to the context.
  • Declare the context variable globally if needed.
  • There are really only 3 things you can do with a PictureBox: Everything else deals with the context:
getContext("2d") Gets the drawing context. Returns the object that the PictureBox Context functions use. "2d" is currently the only valid argument.
refresh() Redraws the entire PictureBox. Required after resizing the box or scrolling.
toDataURL(type) Returns the current picturebox in a Base64 string image. If type is not specified, it is in PNG format. Type can also be "image/jpeg" or "image/gif".


Drawing

arc(x, y, radius, startAngle, endAngle, counterclockwise) Adds an arc to the current path using a radius and specified angles(in radians).
arcTo(x1, y1, x2, y2, radius) Adds an arc of a circle to the current sub path by using a radius and tangent points.
beginPath() Creates a new path in the canvas and sets the starting point to the coordinate (0,0).
bezierCurveTo(cpx1, cpy1, cpx2, cpy2, x, y) Adds a cubic Bezier's curve to the current sub path using two control points.
clearRect(x, y, width, height) Clears the specified rectangle region and makes it transparent.
closePath() Closes an open path and attempts to draw a straight line from the current point to starting point of the path. The use of closePath() is optional.
fill() Closes the current path and paints the area within it.
fillRect(x, y, width, height) Draws a filled rectangle.
fillStyle gradient|pattern
lineCap Sets style of end caps for a line. "butt", "round" or "square".
lineJoin Set style where two lines meet. "bevel", "round" or "mitre".
lineWidth The current line width, in pixels.
lineTo(x, y) Adds a line segment from the current point to the specified coordinate.
rect(x, y, width, height) Adds a rectangle.
stroke() Actually draws the path you have defined
strokeRect(x, y, width, height) Draws a rectangular outline.
strokeStyle gradient|pattern
strokeText(text, x, y, maxWidth) Draws text (with no fill) on the canvas.
  • Here is an example of some drawing:
  'start by setting our colors.
  pb.strokeStyle = vbBlack
  pb.fillStyle = vbRed
  'Now, we define the lines we want to draw in a path.
  pb.beginPath()
  pb.arc(150,150,50,0,Math.PI*2,True)
  pb.closePath()
  'Path is complete: draw it
  pb.stroke()
  'and paint the area inside the path
  pb.fill()

Text

  • Here are the text functions
fillText(text, x, y) Writes text using current settings of font, textAlign and textBaseline.
font The font to use for text. It is a string with three parts: "style size fontname". style can be normal, italic or bold. Example: "italic 40px Calibri"
measureText(text) Returns a rectangle object with text's size.
strokeText(text, x, y, maxWidth) Draws text (with no fill) on the canvas.
textAlign Controls text alignment. Possible values are start, end, left, right and center.
textBaseline Controls where the text is drawn relative to the starting point. Possible values are top, hanging, middle, alphabetic, ideographic and bottom.
style(x, y, width, height) Any valid style string.
  • Here is some sample code
  pb.textBaseline = "top"
  pb.font="16px sans-serif"
  pb.fillText("This is a picturebox",100,0)

Images

  • Images are loaded asynchronously, since they may take time to load.
  • A global image object needs to be created to load the image into.
  • When load is complete, a function with the image object _onload is called.
  • It can then be drawn on the PictureBox.
myImage=new Image()
  • Here are the image functions:
addImage(image, x, y, width, height) Draw an image.
createImageData(width, height) Creates a new, blank ImageData object.
drawImage(image, x, y, width, height) Draw an image.
getImageData(x,y,height,width) Return the image data for a portion of the image. Includes width, height, data array [rgba].
globalCompositeOperation(source-over, source-atop, source-in, source-out, destination-over, destination-atop, destination-in, destination-out, lighter, copy, xor ) Sets or returns how a source (new) images are drawn onto a destination (existing) image.
putImageData(imgData, x, y, dirtyX, dirtyY, dirtyWidth, dirtyHeight) Puts the image data (from a specified ImageData object) back onto the canvas.
  • Here is how the code looks:
  pb.addImage(myImage)


Sprites

  • PictureBoxes can be moved on the screen so they act as sprites
  • Here we move the complete PictureBox and flip it upside down.
  PictureBox1.Left=PictureBox1.Left+5
  PictureBox1.style.webkitTransform="rotate(180deg)"
  • Animate a sprite by using a SetTimeout function to be run every few milliseconds.
  SetTimeout("moveMario()",10)

Multimedia

Audio

The Audio control is used to play sounds.

  • Sound files can be any common format, including mp3, ogg, uncompressed wav and aac.

Here are some options for it:

autoplay Audio will start playing as soon as ready. Not supported on iOS.
controls Controls will be displayed, such as a Play.
loop Audio will start over again when finished.
preload Audio should be loaded when the page loads. Ignored if autoplay is present.
src The name of the file. For example, Super.wav. It can be in the project folder or on a website. 
Function Button1_onclick()
  Audio1.play()
End Function

Video

The Video control is used to play a video.

  • The video has to be in a specific format. Generally, H.264+AAC+MP4 will work.
autoplay Video will start playing as soon as ready.
controls Controls will be displayed, such as a Play.
loop Video will start over again when finished.
preload Video should be loaded when the page loads. Ignored if autoplay is present.
src The name of the file. For example, http://www.nsbasic.com/videotest.mp4. It should be in the project folder or on a web site. 
Function Button2_onclick()
  Video1.play()
End Function

HTMLView

The HTMLView control is a general purpose control which can be used as a container for various kinds of data.

  • Based on the HTML <div> element
  • It can display any kind of HTML
  • Anything that is valid HTML and assigned to innerHTML will display.
  • If the image is too large for the display area, it can be scrolled.

HTML

  • Pure HTML can be displayed by assigning to innerHTML
  HTMLview1.innerHTML="This is an <b>HTMLview</b> with scrolling.</b><br>" & _
    "<img src=mario.jpg width=100 height=200><br>" & _
    "<img src=mario.jpg width=100 height=200>"
  'reset the scroll area
  HTMLview1.refresh()
  • The refresh() call is needed after adding data to reset the scrolling parameters.
  • Information can be appende to the existing data in the view:
  HTMLview1.innerHTML=HTMLview1.innerHTML & "<br>Length is " & Len(HTMLview1.innerHTML)
  HTMLview1.refresh()

Show a Map

  • Static data returned from a website can be displayed
  • In this example, we are getting an image from Google Maps.
  longitude = 48.8582
  latitude = 2.2945
  zoomsize=18 'specify zoom (0-21; bigger is closer)

  ' fill HTMLview box with GoogleMap with specified center and zoom level
  HTMLview1.innerHTML="<img height=640 width=640 " _
    "src=http://maps.google.com/maps/api/staticmap?" _
    & "center=" latitude & "," & longitude & "&zoom="&zoomsize _
    & "&size=640x640&maptype=hybrid&sensor=false></img>"
  • It's the Eiffel Tower in Paris!

Show HTML file

  • We can also display an HTML file.
  • However, it has to be from the same server.
  htm=ReadFile("year.htm")
  If htm.status = 200 Then      
    HTMLview1.innerHTML=htm.responseText
    HTMLview1.refresh()
  Else
    MsgBox "Could not read file. Are you running from a deployed app? It will not work locally."
  End If
  • ReadFile is a simplified version of AJAX.
  • It reads the entire contents of the file.

Show PDF file

  • pdf files can be included with the app
  HTMLview1.innerHTML="<iframe src='year.pdf' width=310 height=260 ></iframe>"
  HTMLview1.refresh()
  • scrolling is automatically enabled
  • The refresh() resets the scrolling area.

Show YouTube video

  • Embedded YouTube videos can be shown
  • Get the YouTube video ID from YouTube
  • Substitute it in the innerHTML string below
  HTMLview1.innerHTML="<iframe frameborder='0' allowfullscreen " _
    & "src='http://www.youtube.com/embed/eDF7QRC3c3Y?feature=player_detailpage'>" _
    & "</iframe>'"
  HTMLview1.refresh()
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