On 14 July 2014 23:19, Chris Vine <ch...@cvine.freeserve.co.uk> wrote:
>> Suppose I have two functions that are called to draw point and line,
>> something like this:
>> http://pastebin.com/Ancx87EF
>
> This example looks fine.
>
>> But if this is it, it'd re-draws the whole drawing area, so I'd be
>> unable to retain any previously drawn entity.
>
> I don't understand what you mean here.
I meant that, taking an example that I showed earlier, when I call the
on_point_cb() it draws the point like defined and when I call the next
function on_line_cb(), the line is drawn but the previously drawn
point is wiped clean.
IDK maybe this is because I am using queue_draw() which re-draws the
entire widget. But if I understand it correctly, like you suggested
that cairo context is already equipped with clip region and I don't
have to explicitly define this clip_rectangle.
<snip>
>> And that is why I was asking if it could be done something like,
>>
>> void DrawingArea :: on_line_cb()
>> {
>>
>> cr->set_source_rgb(0.0, 0.26, 0.26);
>> cr->save();
>> cr->move_to(0,0);
>> cr->line_to(100,100);
>> cr->restore();
>> cr->stroke();
>>
>> queue_draw();
>> std::cout<<"Line created"<<std::endl;
>> }
>>
>> But this doesn't work because it says that 'cr' is not declared in the
>> scope or something related to this.
>
> As a matter of cairo implementation you need a cairo context to work
> with. That is provided by the on_draw() method (pre-clipped, as I
> said). As a matter of basic C++, the cairo context object needs to be
> visible to the code addressing it, which means it must be in scope.
I've declared the cairo context in the DrawingArea.h file as:
Cairo::RefPtr<Cairo::Context> cr;
And the 'scope error' is resolved but I get the segmentation error.
And on running backtrace I get the following:
(gdb) backtrace
#0 0x00007ffff6e24c84 in Cairo::Context::set_source_rgb(double,
double, double) () from /usr/lib/x86_64-linux-gnu/libcairomm-1.0.so.1
#1 0x000000000040d4ca DrawingArea::on_point_cb (this=0x7cce00)
at /home/src/DrawingArea.cpp:78
What I think is that it is not able to identify the context correctly.
Even though I've declared the 'cr' in .h file, the context cr in
on_draw(const Cairo::RefPtr<Cairo::Context>& cr) might be different.
Confused here. :/
--
Gurjot Singh
Blog: http://bhattigurjot.wordpress.com
"It takes a person who is wide awake to make his dream come true." ~
Roger Babson
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