I am trying to achieve constant speed along the way using LibGDX CatmullRomSpline and Im having problems with its operation. Ive tried to study this topic a lot, including reading the LibGDX wiki, but explaining them to achieve a constant speed really does not make sense, and I could not get them to work. https://github.com/libgdx/libgdx/wiki/Path-interface-&-Splines
In my case, the values of the derivatives are very large (in hundreds), so when dividing the number between 0-1 by the derivative the result is very small, and the movement occurs very slow and still not permanent. So I don’t know exactly how their example works.
In my example, I have a couple of visual aids that match the speed of the ball, the bar at the bottom of the screen increases as the speed increases, and the color also changes from white to red with increasing speed.
In the act () method of MyPath.java, I have two sections commented on starting from [1] and [2]. The first one is normal with variable speed along the way, and the second one is my unsuccessful attempt to get the LibGDX wiki server running at a constant speed. Therefore, simply do not comment on these lines to switch between the two versions.
My idea of constant speed involves calculating the speed based on the total path length (using the approxLength (1000) method on the spline), then using the derivative function to determine the actual speed at a given time and adjusting the percentage value sent to the spline to compensate for changes in speed so that the speed is constant. However, I do not quite understand what the derived function actually represents. Earlier, I asked a question about the function of derivatives, but based on the comment I received, I realized that it is easier to ask about achieving a constant speed. Here is my previous question about a derived function:
Derived value of LibGDX CatmullRomSpline?
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http://dropshots.com/Tekker/date/2015-09-19
:
DesktopLauncher.java: ( 1000)
public class DesktopLauncher {
public static void main (String[] arg) {
LwjglApplicationConfiguration config = new LwjglApplicationConfiguration();
config.width = 1000;
config.height = 1000;
new LwjglApplication(new TEST(), config);
}
}
TEST.java:
public class TEST extends Game {
Stage stage;
MyPath path;
@Override
public void create () {
stage = new Stage();
stage.setViewport(new ScreenViewport(stage.getViewport().getCamera()));
Gdx.input.setInputProcessor(stage);
path = new MyPath(1000, 1000);
stage.addActor(path);
}
@Override
public void render () {
Gdx.gl.glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
stage.act(Gdx.graphics.getDeltaTime());
stage.draw();
}
@Override
public void dispose(){
stage.dispose();
super.dispose();
}
}
MyPath.java:
public class MyPath extends WidgetGroup {
Image start, end, path, bar1, horizontal;
float time, percent, dVal, pathLength, dMax=1000, cycle=6, maxPercent, deltaCycle;
CatmullRomSpline<Vector2> catmull;
Vector2 result = new Vector2();
Vector2 previousResult = new Vector2(50,150);
Vector2 derivative = new Vector2();
Vector2 previousDerivative = new Vector2();
Vector2[] points = {
new Vector2(50,150), new Vector2(50,150),
new Vector2(400,800), new Vector2(600,150), new Vector2(700,400),
new Vector2(860,150), new Vector2(860,150)
};
boolean print = true;
public MyPath(int width, int height){
this.setSize(width, height);
catmull = new CatmullRomSpline<Vector2>(points, false);
createPath();
createBar();
pathLength = catmull.approxLength(1000);
}
@Override
public void act(float delta){
catmull.valueAt(result, percent);
path.setPosition(result.x, this.getHeight() - result.y);
updateSpeedVisuals();
debugPrint();
previousResult.set(result);
}
private void createPath(){
start = new Image(new Texture("dot.png"));
start.setColor(Color.GRAY);
start.setPosition(50, this.getHeight() - 150);
this.addActor(start);
end = new Image(new Texture("dot.png"));
end.setColor(Color.GRAY);
end.setPosition(860, this.getHeight() - 150);
this.addActor(end);
path = new Image(new Texture("dot.png"));
path.setColor(Color.WHITE);
this.addActor(path);
}
private void createBar(){
Texture texture = new Texture("ninepatch.png");
int crop = (int)(texture.getWidth()/2)-1;
NinePatch patch9 = new NinePatch(texture, crop, crop, crop, crop);
bar1 = new Image(patch9);
bar1.setColor(Color.GRAY);
bar1.setPosition(5, this.getHeight()-900);
this.addActor(bar1);
}
private void updateSpeedVisuals(){
catmull.derivativeAt(derivative, percent);
dVal = derivative.len() / dMax;
path.setColor(1f, 1f-dVal, 1f-dVal, 1f);
bar1.setWidth(derivative.len());
bar1.setColor(1f, 1f-dVal, 1f-dVal, 1f);
}
private void debugPrint(){
maxPercent = (percent > maxPercent) ? percent : maxPercent;
if (maxPercent > percent){
print = false;
}
if (print){
String debugPrint = "";
debugPrint = debugPrint + "pathLength=" + pathLength + "\t";
debugPrint = debugPrint + "derivative=" + derivative.len() + "\t";
System.out.println(debugPrint);
}
}
}