Drawing With 'Layers'

[Everydaydiesel]

Hello,

I am trying to draw in 'layers' but the code is not exactly doing what I intended.
Here is the input to the program (always png/bmp)

Input.png (7.26 KiB) Viewed 1559 times

What I want it to do is draw the line BEHIND the text. I think the way I do this is with the following steps (I could be wrong)
1. Load the image (always a white background / black(dark) text)
2. Make the background transparent
3. Draw the background (white)
4. Draw the line
5. Draw the text

Here is the code but the line is not under the text (it is drawn on top)

Code: Select all

    wxBitmap bmp(463, 105, 32);
    wxMask *pmask = new wxMask(bmp, wxColour(255, 255, 255));
    bmp.SetMask(pmask);
    bmp.LoadFile("Input.png"); // , wxBITMAP_PNG());
    wxMemoryDC memDC(bmp);
    memDC.SetBackground(*wxTRANSPARENT_BRUSH);
    memDC.SetBackgroundMode(wxTRANSPARENT);
    memDC.SetPen(*wxRED_PEN);
    memDC.DrawLine(25, 61, 427, 61);  // for testing purposes
    memDC.SelectObject( wxNullBitmap );
    bmp.SaveFile("TestOutput.png", wxBITMAP_TYPE_PNG);
  

Thanks in advance for any help you can give

Actual Output:

ActualOutput.png (7.25 KiB) Viewed 1559 times

Target Output:

TargetOutput.png (7.35 KiB) Viewed 1559 times

[Everydaydiesel]

Here is the enlarged version of the ouput


Actual Output:

ActualOutputEnlarged.png (4.25 KiB) Viewed 1554 times

Target Output:

TargetOutputEnlarged.png (4.19 KiB) Viewed 1554 times

[doublemax]

Create a wxMask based on the background color. Call wxBitmap::SetMask(), then draw.

[Everydaydiesel]

Thank you for the reply. I thought I was doing that? Maybe LoadFile clears the mask out?

Code: Select all

    wxBitmap bmp(463, 105, 32);
    wxMask *pmask = new wxMask(bmp, wxColour(255, 255, 255));
    bmp.SetMask(pmask);
    bmp.LoadFile("Input.png"); 

edit: I tried the DrawBitmap function after DrawLine but it still did not work.

Code: Select all

    wxBitmap bmp(463, 105, 32);
    wxMask *pmask = new wxMask(bmp, wxColour(255, 255, 255));
    bmp.SetMask(pmask);
    bmp.LoadFile("Input.png");
    wxMemoryDC memDC(bmp);
    memDC.SetBackground(*wxTRANSPARENT_BRUSH);
    memDC.SetBackgroundMode(wxTRANSPARENT);
    wxColour col;
    memDC.SetPen(*wxRED_PEN);
    memDC.DrawLine(25, 61, 427, 61);
    memDC.DrawBitmap(bmp, 0, 0, true);
    memDC.SelectObject( wxNullBitmap );
    bmp.SaveFile("TestOutput.png", wxBITMAP_TYPE_PNG);

[doublemax]

Creating and setting the mask needs to happen after loading. (The mask is created from the image data).

[Everydaydiesel]

Thanks. I think I am getting closer. This code creates this but it is not drawing the red line for some reason. (the background is transparent)

TestOutput.png (7.46 KiB) Viewed 1514 times

Code: Select all

    wxBitmap bmp(463, 105, 32);
    bmp.LoadFile("Input.png");

    wxMemoryDC memDC(bmp);
    memDC.SetBackground(*wxTRANSPARENT_BRUSH);
    memDC.SetBackgroundMode(wxTRANSPARENT);
    wxMask *pmask = new wxMask(bmp, wxColour(255, 255, 255));
    bmp.SetMask(pmask);
    
    memDC.SetBackground(*wxWHITE_BRUSH);  // this isnt working
    memDC.SetPen(*wxRED_PEN);
    memDC.DrawLine(25, 61, 427, 61);
    memDC.DrawBitmap(bmp, 0, 0, true);
    memDC.SelectObject( wxNullBitmap );
    bmp.SaveFile("TestOutput.png", wxBITMAP_TYPE_PNG);

[doublemax]

Try this:

Code: Select all

    wxBitmap bmp("Input.png", wxBITMAP_TYPE_ANY);

    wxMask *pmask = new wxMask(bmp, wxColour(255, 255, 255));
    bmp.SetMask(pmask);

    wxMemoryDC memDC(bmp);
    memDC.SetPen(*wxRED_PEN);
    memDC.DrawLine(25, 61, 427, 61);
    memDC.SelectObject( wxNullBitmap );
    
    bmp.SaveFile("TestOutput.png", wxBITMAP_TYPE_PNG);

[Everydaydiesel]

I tried that code but the line is still on top of the text instead of underneath

OutputEnlarged.png (4.07 KiB) Viewed 1504 times

[doublemax]

Ok. After studying the documentation, it seems that the mask is only used when reading from the bitmap, not writing into it. This requires a new strategy

Tested:

Code: Select all

wxBitmap bmp("d:\\Input.png", wxBITMAP_TYPE_ANY);

wxMask *pmask = new wxMask(bmp, *wxWHITE);
bmp.SetMask(pmask);

wxBitmap target(bmp.GetWidth(), bmp.GetHeight(), 24 );

wxMemoryDC memDC(target);
memDC.SetBackground(*wxWHITE);
memDC.Clear();

memDC.SetPen(*wxRED_PEN);
memDC.DrawLine(25, 61, 427, 61);

memDC.DrawBitmap( bmp, 0, 0, true );

memDC.SelectObject( wxNullBitmap );

target.SaveFile("d:\\TestOutput.png", wxBITMAP_TYPE_PNG);

This draws the red line first, then draws the masked bitmap on top. The result is not perfect, because of the grey pixels which get not masked.

[Everydaydiesel]

Does it draw a line on yours? When I try it on mine it doesnt draw the red line.

build 2017-09-30, 18:21:54 wx3.0.3 (Linux, unicode) 64 bit

[doublemax]

Yes, here's my result:

TestOutput.png (6.58 KiB) Viewed 1493 times

I tested under Windows though.