libGdx：在舞台上画线并保持在那里

Question

I am working on an app, where I need to draw the trace of my Sprites. I tried to do it with a ShapeRenderer, and it draws the Lines correctly, but after the line was drawn, it gets erased again. So I tried to do it with a Polyline, and add the Points with each update, but after some time this polyline is too large to draw.

I have my code in an overriden Actor class, which on every draw call checks if the sprite has moved, and if so, the line gets drawn with the ShapeRenderer. Is there a way, to keep that line ?

Code:

ShapeRenderer renderer = StageActivity.stageListener.shapeRenderer;
renderer.setColor(color);
Gdx.gl.glLineWidth(strokeWidth);
line.add(sprite.look.getX());
line.add(sprite.look.getY());
renderer.polyline(getLineVertices());

The getLineVertices() Method is just converting my ArrayList to a float[] array.

EDIT:

Since the code above has very poor Performance with a lot of Lines, I tried out the Framebuffer which is essentially what I need (I think), but it does not get draw, what am I doing wrong ?

buffer.begin();
renderer.begin(ShapeRenderer.ShapeType.Line);
renderer.line(previousPoint.x, previousPoint.y, sprite.look.getX(), sprite.look.getY());
renderer.end();
buffer.end();
batch.draw(buffer.getColorBufferTexture(), 0, 0);

The Buffer is a global variable in my Actor.

Answer 1

You should keep lines points in some collections when it is necessary to update and draw lines from these collections in your render method independently

    Array<Vector2> lines = new Array<Vector2>();

    ...

    //when you need to draw next line you just update lines array
    lines.add(new Vector2(sprite.look.getX(), sprite.look.getY()));

    //and in your render method you're just rendering these lines independently
    if(lines.size() > 1) { //one point is not a line
        for(int i = 1; i < lines.size(); i++)
            renderer.line(lines.get(i-1), lines.get(i));
    }

---

Also consider not drawing all lines all the time - if count of lines will be very big (like thousands) you will have performance issues anyway - drawing is rather expensive operation

Answer 2

I resolved my Issue with the framebuffer. It was not rendering, because I had to call batch.end() before calling framebuffer.getColorBufferTexture().