Android Open Source - opengl Square

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License

The source code is released under:

Apache License

Java Source Code

package edu.cs4730.OpenGlDemo1;
/*from   w  w  w .  ja  v a  2  s  .c o  m*/
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;

//there is both GL10 Es 1.0 and GL11 ES 1.1
//much of GL11 subclasses GL10, but some methods only take GL10.
import javax.microedition.khronos.opengles.GL10;
import javax.microedition.khronos.opengles.GL11;

/*
 * A vertex shaded square
 */
public class Square {

  private FloatBuffer mFVertexBuffer;
  private ByteBuffer mColorBuffer;
  private ByteBuffer mIndexBuffer;
  
  public Square() {
    //we are defining our square. For larger objects, we would likely read this in from a file. 
    float vertices[] = {
      -1.0f, 1.0f,
       -1.0f, -1.0f,
      1.0f,  -1.0f,
       1.0f,  1.0f,
    };
    byte maxColor=(byte)255;
    //we are defining colors similar to the square
    //where there are four components: red, green, blue, and alpha (transparency)
    //These map directory to our 4 vertices in the square.
    //using bytes, instead of floats is for space saving (plus floats will get converted to bytes anyway, so save both space and time)
    byte colors[] = {
      maxColor, 0, 0, maxColor,
      maxColor, 0,0, maxColor,
      maxColor,0,0,maxColor,
      maxColor,0,0,maxColor
    };
/*    byte colors[] = {
        maxColor, maxColor, 0, maxColor,
        0, maxColor,maxColor, maxColor,
        0,0,0,maxColor,
        maxColor,0,maxColor,maxColor
      };
      */
    // this matches up the vertices to specific triangles, the first triples says vertices 0,3,1 make triangle 0, 
    byte indices[] =  {
        0, 1, 2,
        0, 2, 3
    };
    //The rest matches up everything, converts their internal java formats to the OpenGL
    //mainly makes sure the ordering of the bytes is correctly, otherwise depending on hardware, they might get reversed.
    ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length*4);
    vbb.order(ByteOrder.nativeOrder());
    mFVertexBuffer = vbb.asFloatBuffer();
    mFVertexBuffer.put(vertices);
    mFVertexBuffer.position(0);
    
    mColorBuffer = ByteBuffer.allocateDirect(colors.length);
    mColorBuffer.put(colors);
    mColorBuffer.position(0);
    
    mIndexBuffer = ByteBuffer.allocateDirect(indices.length);
    mIndexBuffer.put(indices);
    mIndexBuffer.position(0);
  }
  /*
   * method called when we want to render this square.
   * in this case, from SquareRenderer.drawFrame()
   */
  public void draw(GL10 gl) {  
    //tell openGL how the vertices are ordering their faces
    //this is both for efficiently so openGL can ignore the "backside" and not attempt to draw it.
    gl.glFrontFace(GL11.GL_CCW);  //counter clockwise, so any counter triangles are ignored.
    //send the buffers to the renderer
    //specific the number of elements per vertex, which there are 2.
    gl.glVertexPointer(2, GL11.GL_FLOAT, 0, mFVertexBuffer); //8
    //color buffer is added, with the size of the 4 elements
    gl.glColorPointer(4, GL11.GL_UNSIGNED_BYTE, 0, mColorBuffer); //9
    
    //finally draw the element, we the connectivity array, using triangles
    //could also be triangle lists, points or lines
    gl.glDrawElements(GL11.GL_TRIANGLES, 6, GL11.GL_UNSIGNED_BYTE, mIndexBuffer);
    
    //return the openGL back to the default value.
    gl.glFrontFace(GL11.GL_CCW); //11
  }
}

Java Source Code List

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