Simple 3D Shape faces not rendering as expected - OpenGL ES in Android Studio - android-studio

Question

I am trying to make a rotating octahedron display correctly, I have successfully achieved other shapes such as a cube and tetrahedron, but I am experiencing some difficulty with this one.
Here is the simple obj file I am using:
v 0 -1 0
v 1 0 0
v 0 0 1
v -1 0 0
v 0 1 0
v 0 0 -1
#
f 1 2 3
f 4 1 3
f 5 4 3
f 2 5 3
f 2 1 6
f 1 4 6
f 4 5 6
f 5 2 6
My code is as follows:
class Shape(context: Context) {
private var mProgram: Int = 0
// Use to access and set the view transformation
private var mMVPMatrixHandle: Int = 0
//For Projection and Camera Transformations
private var vertexShaderCode = (
// This matrix member variable provides a hook to manipulate
// the coordinates of the objects that use this vertex shader
"uniform mat4 uMVPMatrix;" +
"attribute vec4 vPosition;" +
//"attribute vec4 vColor;" +
//"varying vec4 vColorVarying;" +
"void main() {" +
// the matrix must be included as a modifier of gl_Position
// Note that the uMVPMatrix factor *must be first* in order
// for the matrix multiplication product to be correct.
" gl_Position = uMVPMatrix * vPosition;" +
//"vColorVarying = vColor;"+
"}")
private var fragmentShaderCode = (
"precision mediump float;" +
"uniform vec4 vColor;" +
//"varying vec4 vColorVarying;"+
"void main() {" +
//" gl_FragColor = vColorVarying;" +
" gl_FragColor = vColor;" +
"}")
internal var shapeColor = arrayOf<FloatArray>(
//front face (grey)
floatArrayOf(0f, 0f, 0f, 1f), //black
floatArrayOf(0f, 0f, 1f, 1f),
floatArrayOf(0f, 1f, 0f, 1f),
floatArrayOf(1f, 0f, 0f, 1f), // red
floatArrayOf(1f, 1f, 0f, 1f),
floatArrayOf(1f, 0f, 1f, 1f),
floatArrayOf(1f, 0f, 1f, 1f),
floatArrayOf(0f, 1f, 1f, 1f)
)
private var mPositionHandle: Int = 0
private var mColorHandle: Int = 0
// var objLoader = ObjLoader(context, "tetrahedron.txt")
// var objLoader = ObjLoader(context, "cube.txt")
var objLoader = ObjLoader(context, "octahedron.txt")
var shapeCoords: FloatArray
var numFaces: Int = 0
var vertexBuffer: FloatBuffer
var drawOrder: Array<ShortArray>
lateinit var drawListBuffer: ShortBuffer
init {
//assign coordinates and order in which to draw them (obtained from obj loader class)
shapeCoords = objLoader.vertices.toFloatArray()
drawOrder = objLoader.faces.toTypedArray()
numFaces = objLoader.numFaces
// initialize vertex byte buffer for shape coordinates
val bb = ByteBuffer.allocateDirect(
// (# of coordinate varues * 4 bytes per float)
shapeCoords.size * 4
)
bb.order(ByteOrder.nativeOrder())
vertexBuffer = bb.asFloatBuffer()
vertexBuffer.put(shapeCoords)
vertexBuffer.position(0)
// create empty OpenGL ES Program
mProgram = GLES20.glCreateProgram()
val vertexShader = loadShader(
GLES20.GL_VERTEX_SHADER,
vertexShaderCode
)
val fragmentShader = loadShader(
GLES20.GL_FRAGMENT_SHADER,
fragmentShaderCode
)
// add the vertex shader to program
GLES20.glAttachShader(mProgram, vertexShader)
// add the fragment shader to program
GLES20.glAttachShader(mProgram, fragmentShader)
// creates OpenGL ES program executables
GLES20.glLinkProgram(mProgram)
}
var vertexStride = COORDS_PER_VERTEX * 4 // 4 bytes per vertex
fun draw(mvpMatrix: FloatArray) { // pass in the calculated transformation matrix
for (face in 0 until numFaces) {
// Add program to OpenGL ES environment
GLES20.glUseProgram(mProgram)
// get handle to vertex shader's vPosition member
mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition")
// get handle to fragment shader's vColor member
mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor")
// Enable a handle to the cube vertices
GLES20.glEnableVertexAttribArray(mPositionHandle)
// Prepare the cube coordinate data
GLES20.glVertexAttribPointer(
mPositionHandle, COORDS_PER_VERTEX,
GLES20.GL_FLOAT, false,
vertexStride, vertexBuffer
)
GLES20.glUniform4fv(mColorHandle, 1, shapeColor[face], 0)
// get handle to shape's transformation matrix
mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix")
// Pass the projection and view transformation to the shader
GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0)
// initialize byte buffer for the draw list
var dlb = ByteBuffer.allocateDirect(
// (# of coordinate values * 2 bytes per short)
drawOrder[face].size * 2
)
dlb.order(ByteOrder.nativeOrder())
drawListBuffer = dlb.asShortBuffer()
drawListBuffer.put(drawOrder[face])
drawListBuffer.position(0)
GLES20.glDrawElements(
GLES20.GL_TRIANGLES,
dlb.capacity(),
GLES20.GL_UNSIGNED_SHORT,
drawListBuffer //position indices
)
}
// Disable vertex array
GLES20.glDisableVertexAttribArray(mMVPMatrixHandle)
}
companion object {
// number of coordinates per vertex in this array
internal var COORDS_PER_VERTEX = 3
}
}
class MyGLRenderer1(val context: Context) : GLSurfaceView.Renderer {
private lateinit var mShape: Shape
#Volatile
var mDeltaX = 0f
#Volatile
var mDeltaY = 0f
#Volatile
var mTotalDeltaX = 0f
#Volatile
var mTotalDeltaY = 0f
private val mMVPMatrix = FloatArray(16)
private val mProjectionMatrix = FloatArray(16)
private val mViewMatrix = FloatArray(16)
private val mRotationMatrix = FloatArray(16)
private val mAccumulatedRotation = FloatArray(16)
private val mCurrentRotation = FloatArray(16)
private val mTemporaryMatrix = FloatArray(16)
override fun onDrawFrame(gl: GL10?) {
// Redraw background color
// Redraw background color
GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT or GLES20.GL_DEPTH_BUFFER_BIT)
val scratch = FloatArray(16)
// Create a rotation transformation for the square
Matrix.setIdentityM(mRotationMatrix, 0)
Matrix.setIdentityM(mCurrentRotation, 0)
Matrix.rotateM(mCurrentRotation, 0, mDeltaX, 0.0f, 1.0f, 0.0f)
// Matrix.rotateM(mCurrentRotation, 0, mDeltaY, 1.0f, 0.0f, 0.0f)
// Multiply the current rotation by the accumulated rotation, and then set the accumulated
// rotation to the result.
Matrix.multiplyMM(
mTemporaryMatrix,
0,
mCurrentRotation,
0,
mAccumulatedRotation,
0
)
System.arraycopy(mTemporaryMatrix, 0, mAccumulatedRotation, 0, 16)
// Rotate the cube taking the overall rotation into account.
Matrix.multiplyMM(
mTemporaryMatrix,
0,
mRotationMatrix,
0,
mAccumulatedRotation,
0
)
System.arraycopy(mTemporaryMatrix, 0, mRotationMatrix, 0, 16)
// Set the camera position (View matrix)
Matrix.setLookAtM(mViewMatrix, 0, 2f, 2f, -5f, 0f, 0f, 0f, 0f, 1.0f, 0.0f)
//Calculate the projection and view transformation
Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mViewMatrix, 0)
// Combine the rotation matrix with the projection and camera view
// Note that the mMVPMatrix factor *must be first* in order
// for the matrix multiplication product to be correct.
Matrix.multiplyMM(scratch, 0, mMVPMatrix, 0, mRotationMatrix, 0)
gl?.glDisable(GL10.GL_CULL_FACE)
// Draw shape
mShape.draw(scratch)
}
override fun onSurfaceChanged(gl: GL10?, width: Int, height: Int) {
GLES20.glViewport(0, 0, width, height);
val ratio: Float = width.toFloat() / height.toFloat()
// this projection matrix is applied to object coordinates
// in the onDrawFrame() method
Matrix.frustumM(mProjectionMatrix, 0, -ratio, ratio, -1.0f, 1.0f, 3.0f, 7.0f)
}
override fun onSurfaceCreated(gl: GL10?, config: EGLConfig?) {
GLES20.glEnable(GLES20.GL_DEPTH_TEST)
// initialize a square
mShape = Shape(context)
// Initialize the accumulated rotation matrix
Matrix.setIdentityM(mAccumulatedRotation, 0)
}
}
fun loadShader(type: Int, shaderCode: String): Int {
return GLES20.glCreateShader(type).also { shader ->
GLES20.glShaderSource(shader, shaderCode)
GLES20.glCompileShader(shader)
}
}
class ObjLoader(context: Context, file: String) {
var numFaces: Int = 0
var vertices = Vector<Float>()
var normals = Vector<Float>()
var textures = Vector<Float>()
var faces = mutableListOf<ShortArray>()
init {
val reader: BufferedReader
val isr = InputStreamReader(context.assets.open(file))
reader = BufferedReader(isr)
var line = reader.readLine()
// read file until EOF
while (line != null) {
val parts = line.split((" ").toRegex()).dropLastWhile({ it.isEmpty() }).toTypedArray()
when (parts[0]) {
"v" -> {
var part1 = parts[1].toFloat()
var part2 = parts[2].toFloat()
var part3 = parts[3].toFloat()
// vertices
vertices.add(part1)
vertices.add(part2)
vertices.add(part3)
}
"vt" -> {
// textures
textures.add(parts[1].toFloat())
textures.add(parts[2].toFloat())
}
"vn" -> {
// normals
normals.add(parts[1].toFloat())
normals.add(parts[2].toFloat())
normals.add(parts[3].toFloat())
}
"f" -> {
// faces: vertex/texture/normal
faces.add(shortArrayOf(parts[1].toShort(), parts[2].toShort(), parts[3].toShort()))
println("dbg: points are "+ parts[1]+" "+parts[2]+" "+parts[3])
}
}
line = reader.readLine()
}
numFaces = faces.size
}}
The shape produced can be seen in the following screenshots, it is also visible on the black surface that there is possibly some sort of z fighting taking place? The black triangle flickers red and yellow:
Sometimes the following shapes are produced, flickering in and out of existence, in different colours:
Any help is much appreciated, thanks in advance.
Edit:
I have managed to make the vertices plot correctly thanks to the below answer however there is still this flickering going on, I really appreciate the help.

Answer 1

Array indices start at 0, but Wavefront (.obj) indices start at 1:
faces.add(shortArrayOf(parts[1].toShort(), parts[2].toShort(), parts[3].toShort()))
faces.add(shortArrayOf(
parts[1].toShort()-1, parts[2].toShort()-1, parts[3].toShort()-1))