SkyBox.java

// Copyright 2009 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.android.stardroid.renderer;

import android.util.Log;

import com.google.android.stardroid.renderer.util.ColorBuffer;
import com.google.android.stardroid.renderer.util.IndexBuffer;
import com.google.android.stardroid.renderer.util.TextureManager;
import com.google.android.stardroid.renderer.util.VertexBuffer;
import com.google.android.stardroid.units.GeocentricCoordinates;
import com.google.android.stardroid.units.Vector3;
import com.google.android.stardroid.util.MathUtil;
import com.google.android.stardroid.util.VectorUtil;

import javax.microedition.khronos.opengles.GL10;

public class SkyBox extends RendererObjectManager {
  
  public SkyBox(int layer, TextureManager textureManager) {
    super(layer, textureManager);
    
    int numVertices = NUM_VERTEX_BANDS * NUM_STEPS_IN_BAND;
    int numIndices = (NUM_VERTEX_BANDS-1) * NUM_STEPS_IN_BAND * 6;
    mVertexBuffer.reset(numVertices);
    mColorBuffer.reset(numVertices);
    mIndexBuffer.reset(numIndices);
    
    float[] sinAngles = new float[NUM_STEPS_IN_BAND];
    float[] cosAngles = new float[NUM_STEPS_IN_BAND];
    
    float angleInBand = 0;
    float dAngle = MathUtil.TWO_PI / (NUM_STEPS_IN_BAND - 1);
    for (int i = 0; i < NUM_STEPS_IN_BAND; i++) {
      sinAngles[i] = MathUtil.sin(angleInBand);
      cosAngles[i] = MathUtil.cos(angleInBand);
      angleInBand += dAngle;
    }
    
    float bandStep = 2.0f / (NUM_VERTEX_BANDS-1) + EPSILON;
    
    VertexBuffer vb = mVertexBuffer;
    ColorBuffer cb = mColorBuffer;
    float bandPos = 1;
    for (int band = 0; band < NUM_VERTEX_BANDS; band++, bandPos -= bandStep) {
      int color;
      if (bandPos > 0) {
        // TODO(jpowell): This isn't really intensity, name it more appropriately.
        // I=70 at bandPos = 1, I=50 at bandPos = 0
        byte intensity = (byte)(bandPos * 20 + 50);
        color = (intensity << 16) | 0xff000000;
      } else {
        // I=40 at bandPos = -1, I=0 at bandPos = 0
        byte intensity = (byte)(bandPos * 40 + 40);
        color = (intensity << 16) | (intensity << 8) | intensity | 0xff000000;
      }
      
      float sinPhi = bandPos > -1 ? MathUtil.sqrt(1 - bandPos*bandPos) : 0; 
      for (int i = 0; i < NUM_STEPS_IN_BAND; i++) {
        vb.addPoint(cosAngles[i] * sinPhi, bandPos, sinAngles[i] * sinPhi);
        cb.addColor(color);
      }
    }
    Log.d("SkyBox", "Vertices: " + vb.size());

    IndexBuffer ib = mIndexBuffer;

    // Set the indices for the first band.
    short topBandStart = 0;
    short bottomBandStart = NUM_STEPS_IN_BAND;
    for (short triangleBand = 0; triangleBand < NUM_VERTEX_BANDS-1; triangleBand++) {
      for (short offsetFromStart = 0; offsetFromStart < NUM_STEPS_IN_BAND-1; offsetFromStart++) {
        // Draw one quad as two triangles.
        short topLeft = (short)(topBandStart + offsetFromStart);
        short topRight = (short)(topLeft + 1);
        
        short bottomLeft = (short)(bottomBandStart + offsetFromStart);
        short bottomRight = (short)(bottomLeft + 1);
        
        // First triangle
        ib.addIndex(topLeft);
        ib.addIndex(bottomRight);
        ib.addIndex(bottomLeft);

        // Second triangle
        ib.addIndex(topRight);
        ib.addIndex(bottomRight);
        ib.addIndex(topLeft);
      }
      
      // Last quad: connect the end with the beginning.
      
      // Top left, bottom right, bottom left
      ib.addIndex((short)(topBandStart + NUM_STEPS_IN_BAND - 1));
      ib.addIndex(bottomBandStart);
      ib.addIndex((short)(bottomBandStart + NUM_STEPS_IN_BAND - 1));
      
      // Top right, bottom right, top left
      ib.addIndex(topBandStart);
      ib.addIndex(bottomBandStart);
      ib.addIndex((short)(topBandStart + NUM_STEPS_IN_BAND - 1));
      
      
      topBandStart += NUM_STEPS_IN_BAND;
      bottomBandStart += NUM_STEPS_IN_BAND;
    }
    Log.d("SkyBox", "Indices: " + ib.size());
  }
  
  @Override
  public void reload(GL10 gl, boolean fullReload) {
    mVertexBuffer.reload();
    mColorBuffer.reload();
    mIndexBuffer.reload();
  }
  
  public void setSunPosition(GeocentricCoordinates pos) {
    mSunPos = pos.copy();
    //Log.d("SkyBox", "SunPos: " + pos.toString());
  }
  
  @Override
  protected void drawInternal(GL10 gl) {
    if (getRenderState().getNightVisionMode()) {
      return;
    }
    
    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
    gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
    
    gl.glEnable(GL10.GL_CULL_FACE);
    gl.glFrontFace(GL10.GL_CW);
    gl.glCullFace(GL10.GL_BACK);
    
    gl.glShadeModel(GL10.GL_SMOOTH);
    
    gl.glPushMatrix();

    // Rotate the sky box to the position of the sun.
    Vector3 cp = VectorUtil.crossProduct(new Vector3(0, 1, 0), mSunPos);
    cp = VectorUtil.normalized(cp);
    float angle = 180.0f / MathUtil.PI * MathUtil.acos(mSunPos.y);
    gl.glRotatef(angle, cp.x, cp.y, cp.z);
    
    mVertexBuffer.set(gl);
    mColorBuffer.set(gl);
    
    mIndexBuffer.draw(gl, GL10.GL_TRIANGLES);
    
    gl.glPopMatrix();
  }
  
  private static final short NUM_VERTEX_BANDS = 8;
  // This number MUST be even
  private static final short NUM_STEPS_IN_BAND = 10;
  
  // Used to make sure rounding error doesn't make us have off-by-one errors in our iterations.
  private static final float EPSILON = 1e-3f;
  
  
  VertexBuffer mVertexBuffer = new VertexBuffer(true);
  ColorBuffer mColorBuffer = new ColorBuffer(true);
  IndexBuffer mIndexBuffer = new IndexBuffer(true);
  GeocentricCoordinates mSunPos = new GeocentricCoordinates(0, 1, 0);
}