Problem applying texture to square in OpenGL

Question

I'm stuck at not being able to map texture to a square in openGLES. I'm trying to display a jpg image on the screen, and in order for me to do that, I draw a square that I want to then map image onto. However all I get as an output is a white square. I don't know what am I doing wrong. And this problem is preventing me from moving forward with my project. I'm using Managed OpenGL ES wrapper for Windows Mobile. I verified that the texture is loading correctly, but I can't apply it to my object. I uploaded sample project that shows my problem here. You would need VS2008 with Windows Mobile 6 SDK to be able to run it. I'm also posting the code of the Form that renders and textures an object here. Any suggestions would be much appreciated, since I've been stuck on this problem for a while, and I can't figure out what am I doing wrong.

    public partial class Form1 : Form
{
    [DllImport("coredll")]
    extern static IntPtr GetDC(IntPtr hwnd);

    EGLDisplay myDisplay;
    EGLSurface mySurface;
    EGLContext myContext;

    public Form1()
    {
        InitializeComponent();
        myDisplay = egl.GetDisplay(new EGLNativeDisplayType(this));

        int major, minor;
        egl.Initialize(myDisplay, out major, out minor);

        EGLConfig[] configs = new EGLConfig[10];
        int[] attribList = new int[] 
        { 
            egl.EGL_RED_SIZE, 5, 
            egl.EGL_GREEN_SIZE, 6, 
            egl.EGL_BLUE_SIZE, 5, 
            egl.EGL_DEPTH_SIZE, 16 , 
            egl.EGL_SURFACE_TYPE, egl.EGL_WINDOW_BIT,
            egl.EGL_STENCIL_SIZE, egl.EGL_DONT_CARE,
            egl.EGL_NONE, egl.EGL_NONE 
        };

        int numConfig;
        if (!egl.ChooseConfig(myDisplay, attribList, configs, configs.Length, out numConfig) || numConfig < 1)
            throw new InvalidOperationException("Unable to choose config.");

        EGLConfig config = configs[0];
        mySurface = egl.CreateWindowSurface(myDisplay, config, Handle, null);
        myContext = egl.CreateContext(myDisplay, config, EGLContext.None, null);

        egl.MakeCurrent(myDisplay, mySurface, mySurface, myContext);
        gl.ClearColor(0, 0, 0, 0);
        InitGL();
    }

    void InitGL()
    {
        gl.ShadeModel(gl.GL_SMOOTH);
        gl.ClearColor(0.0f, 0.0f, 0.0f, 0.5f);
        gl.BlendFunc(gl.GL_SRC_ALPHA, gl.GL_ONE_MINUS_SRC_ALPHA);
        gl.Hint(gl.GL_PERSPECTIVE_CORRECTION_HINT, gl.GL_NICEST);
    }

    public unsafe void DrawGLScene()
    {
        gl.MatrixMode(gl.GL_PROJECTION);
        gl.LoadIdentity();
        gl.Orthof(0, ClientSize.Width, ClientSize.Height, 0, 0, 1);
        gl.Disable(gl.GL_DEPTH_TEST);

        gl.MatrixMode(gl.GL_MODELVIEW);
        gl.LoadIdentity();

        Texture myImage;
        Bitmap Image = new Bitmap(@"\Storage Card\Texture.jpg");
        using (MemoryStream ms = new MemoryStream())
        {
            Image.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);
            myImage = Texture.LoadStream(ms, false);
        }

        float[] rectangle = new float[] {
                0, 0,
                myImage.Width, 0,
                0,  myImage.Height,
                myImage.Width,  myImage.Height
            };

        float[] texturePosition = new float[] {
                0, 0,
                myImage.Width, 0,
                0,  myImage.Height,
                myImage.Width,  myImage.Height
            };

        //Bind texture
        gl.BindTexture(gl.GL_TEXTURE_2D, myImage.Name);
        gl.TexParameteri(gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MIN_FILTER, gl.GL_LINEAR);
        gl.TexParameteri(gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MAG_FILTER, gl.GL_LINEAR);
        gl.EnableClientState(gl.GL_TEXTURE_COORD_ARRAY);
        gl.EnableClientState(gl.GL_VERTEX_ARRAY);

        //draw square and texture it.
        fixed (float* rectanglePointer = &rectangle[0], positionPointer = &texturePosition[0])
        {
            gl.TexCoordPointer(2, gl.GL_FLOAT, 0, (IntPtr)positionPointer);
            gl.VertexPointer(2, gl.GL_FLOAT, 0, (IntPtr)rectanglePointer);
            gl.DrawArrays(gl.GL_TRIANGLE_STRIP, 0, 4);
        }

        gl.DisableClientState(gl.GL_TEXTURE_COORD_ARRAY);
        gl.DisableClientState(gl.GL_VERTEX_ARRAY);

    }

    protected override void OnPaintBackground(PaintEventArgs e)
    {

    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        gl.Clear(gl.GL_COLOR_BUFFER_BIT);

        DrawGLScene();
        egl.SwapBuffers(myDisplay, mySurface);
        gl.Clear(gl.GL_COLOR_BUFFER_BIT);
    }

    protected override void OnClosing(CancelEventArgs e)
    {
        if (!egl.DestroySurface(myDisplay, mySurface))
            throw new Exception("Error while destroying surface.");
        if (!egl.DestroyContext(myDisplay, myContext))
            throw new Exception("Error while destroying context.");
        if (!egl.Terminate(myDisplay))
            throw new Exception("Error while terminating display.");
        base.OnClosing(e);
    }
}

Answer 1

You need to enable texturing:

glEnable( GL_TEXTURE_2D );

before rendering the square.

Answer 2

Thanks for the help! However your suggestion didn't fix the issue. Now the square is black instead of white, but still no texture. I've tried adding gl.Enable(gl.GL_TEXTURE_2D) at every possible position, but the result is still black square.

EDIT: Upps, sorry, top-left corner of my image was black that's why I didn't see anything. Changed the image to have different colors, and now I can see part of the image rendered. It's not mapped propertly, but I can figure that part out. Thanks a lot of the help!!!

Answer 3

If you work with OpenGL|ES also take a look if the glDrawTexImage-Extension is supported (well - it should, it's a core-extension and required, but you never know...)

It won't help you with your problem directly (e.g. you have to enable texturing as well), but glDrawTexImage is a hell lot more efficient than polygon rendering. And it needs less code to write as well.

Answer 4

If you are loading textures from PNG or JPG files using UIImage, CGImage and CGContext, it is very important to set GL_TEXTURE_MIN_FILTER to GL_LINEAR or GL_NEAREST before creating textures, because if you don't do it, all your textures except the last bound will be set to blank white.