Ruby Forum wxRuby > Transparent line in Frame

Hi

Thanks for a great GUI toolkit!

I want to draw transparent lines in a Frame. I have the following setup
but my lines are not transparent.

My colour object is created using:
   transparent_blue = Colour.new(0,0,255,100)

and I draw lines using a pen with this colour:
   @pen = Pen.new(transparent_blue)

In evt_paint of frame I have:
   dc.set_pen(@pen)
   dc.draw_line(x1,y1,x2,y2)

The line is blue but there is no transparency.

I set the alpha level to 100 where 255 is supposed to be completely
opaque.

I'm on Windows XP SP2 and

C:\>ruby --version
ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]

Please help!

Regards, Andreas

Andreas Warberg wrote:
> I want to draw transparent lines in a Frame. I have the following setup
> but my lines are not transparent.
The standard DC doesn't support transparency (except on OS X I think).
But you can instead use wxGraphicsContext which fully supports
transparency, antialiasing and other advanced drawing tools like splines
and transforms. You create one from an ordinary DC like this:

paint.do | dc |
  gdc = Wx::GraphicsContext.create(dc)
  gdc.stroke_line(0, 0, 500, 500)
  # etc
end

Unfortunately the wxWidgets developers decided to make the API to
GraphicsContext different to DC, but the results are worth it for
graphical apps.

alex

Alex Fenton wrote:
> The standard DC doesn't support transparency (except on OS X I think).
> But you can instead use wxGraphicsContext which fully supports
> transparency, antialiasing and other advanced drawing tools like splines
> and transforms. You create one from an ordinary DC like this:
> 
> paint.do | dc |
>   gdc = Wx::GraphicsContext.create(dc)
>   gdc.stroke_line(0, 0, 500, 500)
>   # etc
> end

Thanks! I'm having a bit of trouble, though. Here is a small example I 
use:

require 'wx'
include Wx

App.run do
  frame = Frame.new(nil, :title => 'GraphicsContext example', :width => 
[300,400])

  frame.evt_paint do
    frame.paint do |dc|
      gdc = GraphicsContext.create(dc)
      siz = dc.size
      h, w = siz.height, siz.width
      #dc.draw_line(0,0,w,h)
      gdc.stroke_line(0,0,w,h)
    end
  end

  frame.show
end

It should draw / stroke a diagonal line in the frame. This works if I 
use draw_line.

What am I missing? :)

Andreas

Andreas Warberg wrote:
>   frame.evt_paint do
>     frame.paint do |dc|
>       gdc = GraphicsContext.create(dc)
>       siz = dc.size
>       h, w = siz.height, siz.width
>       #dc.draw_line(0,0,w,h)
>   
      gdc.pen = Wx::Pen.new( Wx::Colour.new(255, 0, 0, 128), 20)
> What am I missing? :)
It seems with GraphicsContext, you need to set some sort of pen before
starting drawing - there is no default pen when it's first created.

alex

Alex Fenton wrote:
> Andreas Warberg wrote:
>>   frame.evt_paint do
>>     frame.paint do |dc|
>>       gdc = GraphicsContext.create(dc)
>>       siz = dc.size
>>       h, w = siz.height, siz.width
>>       #dc.draw_line(0,0,w,h)
>>   
>       gdc.pen = Wx::Pen.new( Wx::Colour.new(255, 0, 0, 128), 20)
>> What am I missing? :)
> It seems with GraphicsContext, you need to set some sort of pen before
> starting drawing - there is no default pen when it's first created.
> 
> alex

Thanks!