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Lighting and glMultMatrixf problem

Started by Spoon Thumb Jul 22, 2012 at 11:25 AM 1 replies 1.8k views

Original Post

Jul 22, 2012 at 11:25 AM

I've written a basic graphics engine for OpenGL-ES 1.1 in Java for Android. I use the following code to orientate the spaceships in my game to point in the direction of travel:
[source lang="java"]gl.glPushMatrix();
transforms.transform(gl);
gl.glLightfv(GL10.GL_LIGHT0, GL10.GL_POSITION, light0Position);
model.drawVertexBufferObjects((GL11) gl);
gl.glPopMatrix();[/source]

[source lang="java"]public void transform(GL10 gl) {
gl.glTranslatef(xyz[0], xyz[1], xyz[2]);
// where xyz holds the coordinates of the spaceship

gl.glScalef(scale,scale,scale);

Orientate(gl);

}[/source]
[source lang="java"]

private FloatBuffer startMatrixFB;
protected void Orientate(GL10 gl){
if(startMatrixFB==null){
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(16 * 4);
byteBuffer.order(ByteOrder.nativeOrder());
startMatrixFB = byteBuffer.asFloatBuffer();
}

startMatrixFB.position(0);

startMatrixFB.put((float) -rightOrientationVector.mX);
startMatrixFB.put((float) -rightOrientationVector.mY);
startMatrixFB.put((float) -rightOrientationVector.mZ);

startMatrixFB.put(0);

startMatrixFB.put((float) upOrientationVector.mX);
startMatrixFB.put((float) upOrientationVector.mY);
startMatrixFB.put((float) upOrientationVector.mZ);

startMatrixFB.put(0);

startMatrixFB.put((float) directionVector.mX);
startMatrixFB.put((float) directionVector.mY);
startMatrixFB.put((float) directionVector.mZ);

startMatrixFB.put(0);

startMatrixFB.put(0);
startMatrixFB.put(0);
startMatrixFB.put(0);
startMatrixFB.put(1);

startMatrixFB.position(0);

gl.glMultMatrixf(startMatrixFB);

}[/source]
The problem is that this doesn't affect the diffuse lighting. The lighting on the ship appears without taking into account the changes made by the Orientate() method. I.e. the light is always in the same place relative to the model:

[attachment=10204:lighting_problem_iridian.png]

If anyone can help me solve this, I'd be most appreciative

Thanks
James

dpadam450

Jul 22, 2012 at 4:39 PM

Thats because you have the light transformed exactly how your model is. Say your model has normals and lets treat the light as a normal as well.

If you rotate your model (and its normals) then you are rotating the light normal as well. Only call glLightfv() after you have applied the camera matrix only.
Identity()
cameramatrix()
glLight()

Identity()
ObjectMatrix()
Draw()

Spoon Thumb

Jul 22, 2012 at 6:48 PM

Ah, thanks! could have sworn I'd already tried that...

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