wxWidgets Discussion Forum

Hello,

We're trying to improve our drawing code using wxGraphicsContext.

The problem is that when drawing filled objects using stippled patterns, the foreground color is ignored
and comes out white. Using a wxClientDC object, the color is correct.

Any idea what would cause this?

Thanks very much.

RSB

OS: Windows 7 Pro
wxWidgets: wxWidgets 3.1.0
Compiler: Visual Studio 15

Here's code snippets and pictures of the two methods used to draw circles:

wxClientDC: ----------------------------------
CREATE_DC;

graphics__set_foreground_color(window_attribute_p,dc,window_attribute_p->active_color_index);
graphics__set_line_width(window_attribute_p,dc,1) ;

graphics__set_clip_region(window_attribute_p,iti_dc,window_attribute_p->clip_region);

graphics__set_alpha(window_attribute_p, dc, alpha) ;

dc->DrawCircle(center_position.x_coord,center_position.y_coord,radius);
----------------------------------

wxGraphicsContext: ----------------------------------
CREATE_DC;

graphics__set_foreground_color(window_attribute_p,dc,window_attribute_p->active_color_index);
graphics__set_line_width(window_attribute_p,dc,1) ;

graphics__set_clip_region(window_attribute_p,iti_dc,window_attribute_p->clip_region);

graphics__set_alpha(window_attribute_p, dc, alpha) ;

wxBitmap bitmap(dc->GetSize()) ;

wxMemoryDC memDC ;
memDC.SelectObject(bitmap) ;

memDC.Blit(0, 0, bitmap.GetWidth(), bitmap.GetHeight(), dc, 0, 0) ;

wxGraphicsContext *pGraphicsContext = wxGraphicsContext::Create(memDC) ;

pGraphicsContext->SetPen(dc->GetPen()) ;
pGraphicsContext->SetBrush(dc->GetBrush()) ;

wxGraphicsPath graphicsPath = pGraphicsContext->CreatePath() ;

graphicsPath.AddCircle((double) center_position.x_coord, (double) center_position.y_coord, (double) radius) ;

wxPolygonFillMode mode = wxODDEVEN_RULE ;

pGraphicsContext->DrawPath(graphicsPath, mode) ;

dc->Blit(0, 0, bitmap.GetWidth(), bitmap.GetHeight(), &memDC, 0, 0) ;

memDC.SelectObject(wxNullBitmap) ;

delete pGraphicsContext ;
----------------------------------

Which method do you use to set the foreground color? I only see wxDC::SetTextForeground which is only relevant for text.

For filled polygons the brush is what determines the color.

Inside this routine,
graphics__set_foreground_color(window_attribute_p,dc,window_attribute_p->active_color_index);

The brush is set as follows:

wxBrush brush = dc->GetBrush();

brush.SetColour( foregroundColour ); // Green
brush.SetStyle( wxBRUSHSTYLE_STIPPLE_MASK_OPAQUE );
brush.SetStipple( *pWX_bitmap );

Is there a dc->SetBrush(brush) following? Otherwise this won't do anything.

Yes, there is.

dc->SetPen(pen);
dc->SetBrush(brush);

What happens if you comment out the two stipple-related calls? Does it draw with the correct color? I think the bitmap does override the color if it doesn't have a mask. In that case just the bitmap is used.

If that's not it, try to create a minimal, compilable sample that shows the issue.

Yes, if I change the brush style to filled and skip the call to SetStipple, it does draw with the correct color.

If the bitmap overrides the color, why does it work using the wxClientDC.

I'll try to come up with a small program.

Thanks very much.

FWIW, i think nobody should use wxClientDC for drawing. Ever.

What about a "normal" wxPaintDC?