Problems with rendering a SkyBox

Question

At the moment I'm writing an Android OpenGL ES 2.0 game but now I get stuck on rendering a SkyBox. Here is my (a bit simplified) code for the SkyBox:

float vertices [] = {-1,1,1,1,1,1,-1,-1,1,1,-1,1,-1,1,-1,1,1,-1,-1,-1,-1,1,-1,-1};
byte drawOrder[] = {1,3,0,0,3,2,4,6,5,5,6,7,0,2,4,4,2,6,5,7,1,1,7,3,5,1,4,4,1,0,6,2,7,7,2,3};

private final void bindTexture()
{
    int shaderTextureUnit = GLES20.glGetUniformLocation(shaderProgram, "u_TextureUnit");

    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_CUBE_MAP, texture);
    GLES20.glUniform1i(shaderTextureUnit, 0);
}

public void draw(float[] viewMatrix) // viewMatrix = Camera = data array
{
    GLES20.glUseProgram(shaderProgram);
    bindTexture(); // Load Texture

    shaderPosition = GLES20.glGetAttribLocation(shaderProgram, "a_Position");
    shaderMatrix = GLES20.glGetUniformLocation(shaderProgram, "u_Matrix");

    // get handle to shape's transformation matrix
    GLES20.glUniformMatrix4fv(shaderMatrix, 1, false, vpMatrix, 0);

    // Prepare the triangle coordinate data
    GLES20.glEnableVertexAttribArray(shaderPosition);
    GLES20.glVertexAttribPointer(shaderPosition, 3, GLES20.GL_FLOAT, false, 0, vertexBuffer);

    // Draw the object to the screen GL_UNSIGNED_BYTE
    GLES20.glDrawElements(GLES20.GL_TRIANGLES, orderBuffer.capacity(), GLES20.GL_UNSIGNED_BYTE, orderBuffer);
    GLES20.glDisableVertexAttribArray(shaderPosition); // Free the position in shader
}

I think this code should be perfect because I got it from an OpenGL for beginners book. My problem now is that it looks like this if I render the SkyBox to the screen. I initialize my Camera with this code and here you have also the code for my touch event. If my considerations are right this should produce a circle around the origin so I can see all sides of the SkyBox.

private float angle = 90;

Matrix.setLookAtM(data, 0,   0, 0, 0,   0, 0, -1,   0, 1, 0); // the viewMatrix
// Z+ out of screen     Z- in screen

public void onTouch()
{
    angle += 2;

    float s = (float) Math.sin(angle * Math.PI / 180);
    float c = (float) Math.cos(angle * Math.PI / 180);

    Matrix.setLookAtM(data, 0,   0, 0, 0,   c, 0, -s,   0, 1,  0); // the viewMatrix
}

The draw Method from the SkyBox is called with the data Matrix from the camera (ViewMatrix) and with disabled depthBuffer. Do you have any ideas why the SkyBox is rendered so strange? What is wrong with my code? Only to be sure that all is right with my shaders here is the code from them:

FragmentShader

precision mediump float; 

uniform samplerCube u_TextureUnit;
varying vec3 v_Position;

void main()                         
{
    gl_FragColor = textureCube(u_TextureUnit, v_Position);    
}

VertexShader

uniform mat4 u_Matrix;
attribute vec3 a_Position;  
varying vec3 v_Position;

void main()                    
{                                                 
    v_Position = a_Position;    
    v_Position.z = -v_Position.z; 

    gl_Position = u_Matrix * vec4(a_Position, 1.0);
    gl_Position = gl_Position.xyww;
}

Answer 1

Im not entirely sure about this myself, but maybe your problem is that you dont have one. From the looks of it, your skybox is rotating correctly. Question now: I see you are initializing and uploading the view-matrix correctly, but what about the projection-matrix, i dont see that one. My guess is that your code is alright so far, but since you havent specified it (the projection), OpenGL defaults to some sort of orthogonal projection, which is why it looks so weird when rotating. Maybe that solves your problem. Regards, Daniel

EDIT: Try using the Matrix.perspectiveM() method and upload the returned matrix to your shader, then multiply it by the view-matrix before multiplying the product of both by your coordinate vector. That should fix your problem, in case you are still waiting for an answer.

Answer 2

Before all I can defenetly say , that disabling ZBuffer is bad idea due perfomance issues, and it looks like for me it is issue. 1) try enable Zbuffer!! 2) check your model,view and project matrices