Efficient use of wxGCDC on a Raspberry PI

[robbiegregg]

Hi all,

I would like to be able to draw a large number (100x100) of filled circles on a grid using a Raspberry PI 2 model B using wxWidgets 3.0 (Raspbian). The OnPaint function I currently have is shown below:

Code: Select all

void temp2Dialog::OnPaint(wxPaintEvent& event)
{
    int borderSize = 4;
    wxBufferedPaintDC pdc(Panel1);
    wxGCDC dc(pdc);
    PrepareDC(dc);
    wxSize totalSize = dc.GetSize();

    // Define where picture is to start (top left corner), noting presence of border
    double g1Position[2] = {0};
    g1Position[0] += borderSize;
    g1Position[1] += borderSize;

    // Define how big the picture can be (i.e. size of wxPanel Panel1), noting presence of border all around
    double g1Size[2] = {0};
    g1Size[0] = totalSize.GetWidth();
    g1Size[1] = totalSize.GetHeight();

    g1Size[0] -= borderSize*2;
    g1Size[1] -= borderSize*2;
    
    // Draw underlying black rectangle
    dc.DrawRectangle(g1Position[0],g1Position[1],g1Size[0],g1Size[1]);

    // Matrix of circles will be square. Work out the maximum length of the square
    double picSize = 0;
    if(g1Size[0] > g1Size[1]) picSize = g1Size[1];
    else picSize = g1Size[0];

    // Work out size of circles
    int matrixSize = 100;
    double deltaX = picSize / matrixSize;
    int ideltaX = (int)deltaX;
    double Radius = deltaX /2.0;
    int iRadius = (int)Radius;
    
    // Loop through the matrix of circles
    for(int i=0;i<matrixSize;i++)
    {
        for(int j=0;j<matrixSize;j++)
        {
            // Define a random colour, and then draw a filled circle
            wxColour randomColour(rand()%255,rand()%255,rand()%255);
            dc.SetBrush(wxBrush(randomColour));
            dc.SetPen(wxPen(randomColour));
            int X = ideltaX*(i+1);
            int Y = ideltaX*(j+1);
            dc.DrawCircle(X,Y,iRadius);
        }
    }
}

I have tried increasing the GPU graphics from 64 mb up to 256 mb and 512 mb (and overclocking the RPI-B CPU), but this does not help. Before deciding the computing power from a RPI is insufficient for my needs, can anyone think of a better way of coding this (retaining the double buffering), resulting in a function that takes a fraction of a second to complete? On my setup this function takes roughly 3-5 seconds when I maximise the window on a 1080p screen.

Ideally, I would also like to retain the use of wxGCDC as this seems to be the only way to ensure the circles are drawn using anti-aliasing.

Thanks very much for reading.

[doublemax]

In your code the only optimization you could make is to use a static buffer bitmap for wxBufferedPaintDC, but that won't make much of a difference.

Realistically i think your only option to achieve the required speed is to use OpenGL for drawing. If it's hardware-accelerated on the Raspberry (and i think it is), then is should be fast enough. And if you only need to draw rectangles and circles, it shouldn't be that much work to implement it.