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 * This software is provided "AS IS," without a warranty of any kind. ALL
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package net.java.joglutils.msg.nodes;

import net.java.joglutils.msg.actions.*;
import net.java.joglutils.msg.math.*;

/** Represents a camera utilizing a perspective projection. <P>

    The default height angle is Math.PI / 4 radians (45 degrees),
    meaning that the camera has a total vertical field of view of 90
    degrees.
*/

public class PerspectiveCamera extends Camera {
  private static final float DEFAULT_HEIGHT_ANGLE = (float) (Math.PI / 4);
  // Amount the most recently set height angle differed from the default
  private float vertFOVScale = 1.0f;
  
  public Mat4f getProjectionMatrix() {
    if (projDirty) {
      projMatrix.makeIdent();
      projDirty = false;

      // Recompute matrix based on current parameters
      float zNear = getNearDistance();
      float zFar  = getFarDistance();
      float deltaZ = zFar - zNear;
      float aspect = getAspectRatio();
      float radians = vertFOVScale * DEFAULT_HEIGHT_ANGLE;
      float sine = (float) Math.sin(radians);
      if ((deltaZ == 0) || (sine == 0) || (aspect == 0)) {
        return projMatrix;
      }
      
      float cotangent = (float) Math.cos(radians) / sine;
      projMatrix.set(0, 0, cotangent / aspect);
      projMatrix.set(1, 1, cotangent);
      projMatrix.set(2, 2, -(zFar + zNear) / deltaZ);
      projMatrix.set(3, 2, -1);
      projMatrix.set(2, 3, -2 * zNear * zFar / deltaZ);
      projMatrix.set(3, 3, 0);
    }

    return projMatrix;
  }

  /** Sets the height angle, in radians, of this perspective camera.
      The default height angle is Math.PI / 4 radians, or 45 degrees. */
  public void setHeightAngle(float heightAngle) {
    vertFOVScale = heightAngle / DEFAULT_HEIGHT_ANGLE;
    projDirty = true;
  }

  /** Returns the height angle, in radians, of this perspective
      camera. */
  public float getHeightAngle() {
    return vertFOVScale * DEFAULT_HEIGHT_ANGLE;
  }

  /** Returns the width angle, in radians, of this perspective
      camera, assuming the passed-in aspect ratio. */
  public float getWidthAngle(float aspectRatio) {
    return (float) Math.atan(aspectRatio * Math.tan(getHeightAngle()));
  }

  /** Returns the width angle, in radians, of this perspective camera,
      assuming the camera's currently-set aspect ratio. */
  public float getWidthAngle() {
    return getWidthAngle(getAspectRatio());
  }

  public void render(GLRenderAction action) {
    // FIXME: unclear whether we should be doing this, or whether we
    // should have a mechanism which doesn't require mutation of the
    // camera
    setAspectRatio(action.getCurAspectRatio());
    doAction(action);
  }
}