3D Graphics - Beginning J2ME: From Novice to Professional - page 285

The rotation and orientation methods take an angle and an axis of revolution as parameters.
preRotate() is applied before the translation, and postRotate() is applied after the translation.
Using these methods, you can manipulate the coefficients in the Transform matrix without
knowing the math involved.
In the Listing 15-1 code, shown earlier in this section, the camera is moved to (0,0, 10) . This
is 10 units towards the viewer along the z-axis. When the camera is first created, it is located at
(0,0,0) and pointing towards the z-axis (into the display).
The single light is also placed in the same position as the camera, giving the camera a
“headlight” pointing at the direction of the view.
The final code in the rendering loop actually rotates the triangle submesh. The same
Transform is reused here to save some memory. Calling setIdentity() on the Transform basically
resets it to a Transform that performs no translation, scaling, or rotation. Then the postRotate()
method is used to rotate the triangle one degree per frame around the axis of choice (z-axis in
this case).
mAngle += 1.0f;
mTransform.setIdentity();
mTransform.postRotate(mAngle, // Rotate 1 degree per frame
0, 0, 1.0f );
mGraphics3D.render(mVertexBuffer, mIndexBuffer,
mAppearance, mTransform);
The call to render() will actually draw a 3D frame into the bound 2D Graphics instance.
The Light and Camera have already been set up earlier using the Graphics3D instance. Notice
how Graphic3D 's render() method takes the VertexBuffer , the IndexBuffer ( TriangleStripArray ),
the Appearance , and the Transform to perform its work.
Experimentation with Culling
TriangleCanvas is a great framework for experimenting with the M3G APIs. You can try moving
the light, camera, and triangle around; or try working with different Material and Appearance
attributes, etc. All you need is a copy of the Javadoc of the JSR 184 for reference.
As an example, we'll disable culling. Disabling culling will let you see the “back” of the
triangle rendered. To add code to disable culling, look inside the init() method and insert the
following highlighted code:
mAppearance.setMaterial(mMaterial);
PolygonMode tPoly = new PolygonMode();
tPoly.setCulling(PolygonMode.CULL_NONE);
mAppearance.setPolygonMode(tPoly);
mBackground.setColor(0x00ee88);
PolygonMode is an M3G class representing a rendering attribute. It is grouped by an Appearance
instance and can be used to control culling. In this code, it is set to CULL_NONE , allowing the back
of the triangle to be rendered. The default is CULL_BACK .
Assuming that you have modified TriangleCanvas to rotate the triangle around the x-axis,
rebuild the MIDlet and run it. You should now see both sides of the triangle rendered during
the rotation. Notice, however, that only the side with the vertex normals is rendered with light
and color.