[SOLVED] Not understanding parallel projection

Troubleshooting graphics
1

I am not understanding parallel projection.

I have this test code:

package jme3;

import com.jme3.app.SimpleApplication;
import com.jme3.material.Material;
import com.jme3.math.ColorRGBA;
import com.jme3.math.FastMath;
import com.jme3.math.Quaternion;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.Mesh;
import com.jme3.scene.debug.Arrow;
import com.jme3.scene.shape.Box;

public class CameraTest extends SimpleApplication {
  @Override
  public void simpleInitApp() {
    Mesh m = new Arrow(Vector3f.UNIT_X);
    Geometry geom = new Geometry("X",m);
    geom.scale(5);
    Material mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Red);
    geom.setMaterial(mat);
    rootNode.attachChild(geom);
    m = new Arrow(Vector3f.UNIT_Y);
    geom = new Geometry("Y",m);
    geom.scale(5);
    mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Green);
    geom.setMaterial(mat);
    rootNode.attachChild(geom);
    m = new Arrow(Vector3f.UNIT_Z);
    geom = new Geometry("Z",m);
    geom.scale(5);
    mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Blue);
    geom.setMaterial(mat);
    rootNode.attachChild(geom);

    m = new Box(1, 1, 1);
    geom = new Geometry("Box", m);
    mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    ColorRGBA bgColor = ColorRGBA.White;
    mat.setColor("Color", bgColor);      
    geom.setMaterial(mat);
    rootNode.attachChild(geom);

    cam.setLocation(new Vector3f(10,10,10));
    Quaternion rotation = new Quaternion().fromAngleAxis(45*FastMath.DEG_TO_RAD,Vector3f.UNIT_Y);
    cam.setRotation(cam.getRotation().mult(rotation));
    rotation = new Quaternion().fromAngleAxis(35*FastMath.DEG_TO_RAD,Vector3f.UNIT_X);
    cam.setRotation(cam.getRotation().mult(rotation));
    cam.setParallelProjection(true);
  }
  
  public static void main(String[] args) {
    CameraTest app = new CameraTest();
    app.start();
  }
}

If I comment out the call to setParallelProjection, I get what I expect:

normal
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But, if I call the setParallelProjection, I get an all white screen which seems to be the box has completely filled the screen. I can turn the camera and see the edges of the box, but can’t move to where I can see the whole thing.

I must be misunderstanding what this does. Can someone please give me some insights?

2

With parallel projection, things do not get smaller as they get farther away. If something completely fills the screen near then it will completely fill the screen far.

So your frustum planes are just too close together. That’s the only way you can control the “size” of what’s in view.

3 Likes
3

Thank you for that. I never worked with a parallel projection before so I did not know about setting the frustrum.

I found a different post with some info so I updated my code and it now gives me what I am expecting. Thank you!

In case it helps anyone, here is my test code:

package jme3;

import com.jme3.app.SimpleApplication;
import com.jme3.material.Material;
import com.jme3.math.ColorRGBA;
import com.jme3.math.FastMath;
import com.jme3.math.Quaternion;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.Mesh;
import com.jme3.scene.debug.Arrow;
import com.jme3.scene.shape.Box;

public class CameraTest extends SimpleApplication {
  @Override
  public void simpleInitApp() {
    Mesh m = new Arrow(Vector3f.UNIT_X);
    Geometry geom = new Geometry("X",m);
    geom.scale(5);
    Material mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Red);
    geom.setMaterial(mat);
    rootNode.attachChild(geom);
    m = new Arrow(Vector3f.UNIT_Y);
    geom = new Geometry("Y",m);
    geom.scale(5);
    mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Green);
    geom.setMaterial(mat);
    rootNode.attachChild(geom);
    m = new Arrow(Vector3f.UNIT_Z);
    geom = new Geometry("Z",m);
    geom.scale(5);
    mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    mat.setColor("Color", ColorRGBA.Blue);
    geom.setMaterial(mat);
    rootNode.attachChild(geom);

    m = new Box(1, 1, 1);
    geom = new Geometry("Box", m);
    mat = new Material(assetManager,"Common/MatDefs/Misc/Unshaded.j3md");
    ColorRGBA bgColor = ColorRGBA.White;
    mat.setColor("Color", bgColor);      
    geom.setMaterial(mat);
    rootNode.attachChild(geom);

    cam.setLocation(new Vector3f(10,10,10));
    Quaternion rotation = new Quaternion().fromAngleAxis(45*FastMath.DEG_TO_RAD,Vector3f.UNIT_Y);
    cam.setRotation(cam.getRotation().mult(rotation));
    rotation = new Quaternion().fromAngleAxis(35*FastMath.DEG_TO_RAD,Vector3f.UNIT_X);
    cam.setRotation(cam.getRotation().mult(rotation));
    cam.setParallelProjection(true);
    float aspect = (float) cam.getWidth() / cam.getHeight();
    float size = 5;
    cam.setFrustum(-1000, 1000, -aspect * size, aspect * size, size, -size);
  }
  
  public static void main(String[] args) {
    CameraTest app = new CameraTest();
    app.start();
  }
}
2 Likes