CODEWITHSUNDEEP
javagraphicsgridjpanel
sokolovic
sokolovic

Reputation: 293

JPanel grid issue

Ok, I am implementing a flowchart editor in Java. My goal is to provide a possibility to display grid lines on a drawing surface. I partially made it to work:

public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;

    // Scrolling
    g2.transform(transformation);   

    // Step one: draw grid
    if(showGrid)
    {
        // Horizontal grid lines
        for(int i = -1; i < getSize().getWidth(); i += 50)
        {
            g2.drawLine(i, 0, i, (int)getSize().getHeight());
        }
        // Vertical grid lines
        for(int i = -1; i < getSize().getHeight(); i += 50)
        {
            g2.drawLine(0, i, (int)getSize().getWidth(), i);
        }
    }

    // Step two: draw symbols
    // ...
}

The results are like this:alt text

But, if I scroll the diagram down or up, I get this: alt text

As seen, diagram is scrolled, but not the grid. I also tried putting Step one code before g2.transform(transformation) line, but after that, if I scroll, grid lines are not moving.

So, the question is: is there a way to draw grid lines and avoid mentioned behavior? The goal is to scroll grid along with other elements on diagram.

  1. List item

Upvotes: 3

Views: 587

Answers (2)

Erick Robertson
Erick Robertson

Reputation: 33078

The grid is being scrolled, but the lines do not extend to the new bounds.

The grid is scrolled along with the objects. That's why there's empty space at the bottom of the second diagram. The top of the grid has been scrolled off the top of the panel. The bottom of the grid has been scrolled above the bottom of the panel. The grid lines have moved.

The only problem I see is that the grid lines should always extend to the extents of the visible area. To do this, you need to reverse the transformation for the getWidth and getHeight and then draw the grid lines on all of the multiples of 50 between those values.

Upvotes: 1

jzd
jzd

Reputation: 23629

Paint the entire diagram and put it into a JScrollPane instead of transforming scroll actions yourself.

Upvotes: 0

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