3D Views: Source Code
Page 7
Programmatic Cube
This Java code is modified from Learn OpenGL ES code posted on GitHub. The WebGL tutorials can be found at http://www.learnopengles.com.
Introduction
The ShapeBuilder class creates a cube programmatically, however as you can see
on page 3, my Java source code uploads specifically prepared vertices and texels
to apply one texture map for each cube view.
Java Code
package com.seventhundersoftware.cubeview.common;
public class ShapeBuilder
{
public static float[] generateCubeData(float[] point1,
float[] point2,
float[] point3,
float[] point4,
float[] point5,
float[] point6,
float[] point7,
float[] point8,
int elementsPerPoint)
{
// Given a cube with the points defined as follows:
// front left top, front right top, front left bottom, front right bottom,
// back left top, back right top, back left bottom, back right bottom,
// return an array of 6 sides, 2 triangles per side, 3 vertices per triangle, and 4 floats per vertex.
final int FRONT = 0;
final int RIGHT = 1;
final int BACK = 2;
final int LEFT = 3;
final int TOP = 4;
final int BOTTOM = 5;
final int size = elementsPerPoint * 6 * 6;
final float[] cubeData = new float[size];
for (int face = 0; face < 6; face ++)
{
// Relative to the side, p1 = top left, p2 = top right, p3 = bottom left, p4 = bottom right
final float[] p1, p2, p3, p4;
// Select the points for this face
if (face == FRONT)
{
p1 = point1; p2 = point2; p3 = point3; p4 = point4;
}
else if (face == RIGHT)
{
p1 = point2; p2 = point6; p3 = point4; p4 = point8;
}
else if (face == BACK)
{
p1 = point6; p2 = point5; p3 = point8; p4 = point7;
}
else if (face == LEFT)
{
p1 = point5; p2 = point1; p3 = point7; p4 = point3;
}
else if (face == TOP)
{
p1 = point5; p2 = point6; p3 = point1; p4 = point2;
}
else // if (side == BOTTOM)
{
p1 = point8; p2 = point7; p3 = point4; p4 = point3;
}
// In OpenGL counter-clockwise winding is default. This means that when we look at a triangle,
// if the points are counter-clockwise we are looking at the "front". If not we are looking at
// the back. OpenGL has an optimization where all back-facing triangles are culled, since they
// usually represent the backside of an object and aren't visible anyways.
// Build the triangles
// 1---3,6
// | / |
// 2,4--5
int offset = face * elementsPerPoint * 6;
for (int i = 0; i < elementsPerPoint; i++) { cubeData[offset++] = p1[i]; }
for (int i = 0; i < elementsPerPoint; i++) { cubeData[offset++] = p3[i]; }
for (int i = 0; i < elementsPerPoint; i++) { cubeData[offset++] = p2[i]; }
for (int i = 0; i < elementsPerPoint; i++) { cubeData[offset++] = p3[i]; }
for (int i = 0; i < elementsPerPoint; i++) { cubeData[offset++] = p4[i]; }
for (int i = 0; i < elementsPerPoint; i++) { cubeData[offset++] = p2[i]; }
}
return cubeData;
}
}
Summary
The ShapeBuilder class creates a cube programmatically, however as you can see
on page 3, my Java source code uploads specifically prepared vertices and texels
to apply one texture map for each cube view.
Java & OpenGL ES
This set of pages include Android Java, combined with OpenGL ES, to display a set of simple three dimensional views. The views apply a unique, simple concept to render 3D backgrounds, without Skyboxes or time consuming shader switching. Each view's contained in one graphic, with room for other sprites and meshes.
Java and OpenGL ES source code was ported from WebGL with only minor changes.
The book, 3D Scenes: Learn WebGL Book 3
, explains implementation
and graphics preparation for the WebGL app, in detail.
