Curves Tool | Castle Game Engine

Curves Tool

Table of Contents

1. Introduction
2. Creating and editing curves
3. Using curves in your own programs

1. Introduction

We have a simple tool to design curves (piecewise cubic Bezier curves). The created curves can be saved into a simple XML format and loaded into your own Castle Game Engine programs and used for any purpose (for example as a track along which something moves).

Download:

Get Castle Game Engine binary release, the tool is readily available as bin/castle-curves .
Or get Castle Game Engine source code, the tool is in tools/castle-curves subdirectory.

The main example how to use designed curves is inside the CGE, in examples/curves/use_designed_curve.

2. Creating and editing curves

For many commands and their key shortcuts, see the program’s menu. Use mouse to create and edit curve points:

Right mouse button click:

Add new curve point. If some curve and point were selected, the new point is added to the selected curve after the selected point. Otherwise, a new new curve with one point is created. So if you want to start creating 2nd curve, just deselect all (key N) and press right mouse button.
Left mouse button click:

Select control point (and it’s curve).
Dragging with left mouse button:

Move selected point. Hold Shift key to move whole selected curve. The smallest drags are ignored at the begging, so we avoid accidental drags when selecting, don’t worry:)
Use keys + and - to smoothly zoom in/out. Use Home to reset zoom to zero.

Tip	use a reference image (menu Background→Load) to fit your curve nicely to your use. By default we show a simple image with a helpful grid.

Save and open menu commands store curves list in a simple XML file. You can use it to load your designed curves into your Castle Game Engine programs, see below.

3. Using curves in your own programs

Load a list of curves from XML file using the TCurveList.LoadFromFile method.
Or load the first curve from XML file using the simpler TCurve.LoadFromFile method.
Query the curve using the TCurve.Point(T) method.
Use T values in the range [0..1] to move along the curve. In general, you should look at the valid range for T in TCurve.TBegin and TCurve.TEnd properties, but in case of castle-curves tool — you know that TBegin is always 0 and TEnd is 1.

See the example below:

program curves_example;

{$apptype console}

uses SysUtils, CastleVectors, CastleFilesUtils, CastleCurves, CastleLog;
var
  FirstCurve: TCurve;
  Curves: TCurveList;
begin
  InitializeLog;

  FirstCurve := TCurve.LoadFromFile('castle-data:/my_curves.xml');
  try
    // That's it, you loaded the 1st curve from XML file.
    // Write some initial curve points.
    WritelnLog(FirstCurve.Point(0.0).ToString);
    WritelnLog(FirstCurve.Point(0.1).ToString);
  finally FreeAndNil(FirstCurve) end;

  { in more complicated scenarios, my_curves.xml may keep many curves
    inside. Load them like this: }

  Curves := TCurveList.Create(true { free objects });
  try
    Curves.LoadFromFile('castle-data:/my_curves.xml');
    if Curves.Count = 0 then
      raise Exception.Create('No curves defined in file');
    FirstCurve := Curves[0];
    // That's it, you have the 1st curve from XML file.
    // Write some initial curve points.
    WritelnLog(FirstCurve.Point(0.0).ToString);
    WritelnLog(FirstCurve.Point(0.1).ToString);
    WritelnLog(FirstCurve.Point(0.2).ToString);
  finally FreeAndNil(Curves) end;
end.

To improve this documentation just edit this page and create a pull request to cge-www repository.