2D Game Programming Tricks - Beginning Android Games - page 402

Listing 8-15. Camera2D.java, Our Shiny New Camera Class for 2D Rendering
package com.badlogic.androidgames.framework.gl;
import javax.microedition.khronos.opengles.GL10;
import com.badlogic.androidgames.framework.impl.GLGraphics;
import com.badlogic.androidgames.framework.math.Vector2;
public class Camera2D {
public final Vector2 position;
public float zoom;
public final float frustumWidth;
public final float frustumHeight;
final GLGraphics glGraphics;
As discussed, we store the camera's position, frustum width and height, and zoom factor as
members. The position and zoom factor are public, so we can easily manipulate them. We also
need a reference to GLGraphics so that we can get the up-to-date width and height of the screen
in pixels for transforming touch coordinates to world coordinates.
public Camera2D(GLGraphics glGraphics, float frustumWidth, float frustumHeight) {
this .glGraphics = glGraphics;
this .frustumWidth = frustumWidth;
this .frustumHeight = frustumHeight;
this .position = new Vector2(frustumWidth / 2, frustumHeight / 2);
this .zoom = 1.0f;
}
In the constructor, we take a GLGraphics instance, and the frustum's width and height at the
zoom factor 1, as parameters. We store them and initialize the position of the camera to look
at the center of the box bounded by (0,0,1) and ( frustumWidth , frustumHeight ,-1), as shown in
Figure 8-19 . The initial zoom factor is set to 1.
public void setViewportAndMatrices() {
GL10 gl = glGraphics.getGL();
gl.glViewport(0, 0, glGraphics.getWidth(), glGraphics.getHeight());
gl.glMatrixMode(GL10. GL_PROJECTION );
gl.glLoadIdentity();
gl.glOrthof(position.x - frustumWidth * zoom / 2,
position.x + frustumWidth * zoom / 2,
position.y - frustumHeight * zoom / 2,
position.y + frustumHeight * zoom / 2,
1, -1);
gl.glMatrixMode(GL10. GL_MODELVIEW );
gl.glLoadIdentity();
}
The setViewportAndMatrices() method sets the viewport to span the whole screen, and sets
the projection matrix in accordance with your camera's parameters, as discussed previously.
At the end of the method, we tell OpenGL ES that all further matrix operations are targeting the