Question

I’m currently loading a cube-map into my application but it’s shown in a red tone.
Edit: The channel problem is also present when using 2D-Textures, it seems the channels are not in the correct order. Is there any way to change the order of the channels using the iOS methods?

That’s the code for texture loading:

public TextureCube (Generic3DView device, UIImage right, UIImage left, UIImage top, UIImage bottom, UIImage front, UIImage back)
    : base(device)
{
    _Device = device;
    GL.GenTextures (1, ref _Handle);
    GL.BindTexture (TextureType, _Handle);
    LoadTexture(All.TextureCubeMapPositiveX, right);
    LoadTexture(All.TextureCubeMapNegativeX, left);
    LoadTexture(All.TextureCubeMapPositiveY, top);
    LoadTexture(All.TextureCubeMapNegativeY, bottom);   
    LoadTexture(All.TextureCubeMapPositiveZ, front);
    LoadTexture(All.TextureCubeMapNegativeZ, back);
        
    GL.TexParameter(All.TextureCubeMap, All.TextureMinFilter, (Int32)All.LinearMipmapLinear);
    GL.TexParameter(All.TextureCubeMap, All.TextureMagFilter, (Int32)All.Linear);
    GL.GenerateMipmap(All.TextureCubeMap);
}
            
private void LoadTexture(All usage, UIImage image) 
{
    GL.TexImage2D(usage, 0, (Int32)All.Rgba, (Int32)image.Size.Width,
                  (Int32)image.Size.Height, 0, All.Rgba, All.UnsignedByte, RequestImagePixelData(image));
}

protected CGBitmapContext CreateARGBBitmapContext (CGImage inImage)
{
    var pixelsWide = inImage.Width;
    var pixelsHigh = inImage.Height;
    var bitmapBytesPerRow = pixelsWide * 4;
    var bitmapByteCount = bitmapBytesPerRow * pixelsHigh;
    //Note implicit colorSpace.Dispose() 
    using (var colorSpace = CGColorSpace.CreateDeviceRGB()) {
         //Allocate the bitmap and create context
         var bitmapData = Marshal.AllocHGlobal (bitmapByteCount);
         if (bitmapData == IntPtr.Zero) {
             throw new Exception ("Memory not allocated.");
         }

         var context = new CGBitmapContext (bitmapData, pixelsWide, pixelsHigh, 8,
                            bitmapBytesPerRow, colorSpace, CGImageAlphaInfo.PremultipliedFirst);
         if (context == null) {
              throw new Exception ("Context not created");
         }
         return context;
     }
}

//Store pixel data as an ARGB Bitmap
protected IntPtr RequestImagePixelData (UIImage inImage)
{
     var imageSize = inImage.Size;
     CGBitmapContext ctxt = CreateARGBBitmapContext (inImage.CGImage);
     var rect = new RectangleF (0.0f, 0.0f, imageSize.Width, imageSize.Height);
     ctxt.DrawImage (rect, inImage.CGImage);
     var data = ctxt.Data;
     return data;
}

I think the channels are inverted, but maybe there is a way to invert the bitmap without some custom code.

This is the image which is rendered( ignore the fancy model in front of it ):

And the expected image:

Edit:

The GL_INVALID_OPERATION issue has been fixed, but it does not solve the issue with the red texture.

The vertex-shader:

attribute vec3 position;            
uniform mat4 modelViewMatrix;           

varying mediump vec3 texture;           
        
void main()
{   
    texture = position.xyz;         
    gl_Position = modelViewMatrix * vec4(position.xyz, 1.0);    
}

The fragment-shader:

varying mediump vec3 texture;
uniform samplerCube cubeMap;        
        
void main()
{
    mediump vec3 cube = vec3(textureCube(cubeMap, texture));
    gl_FragColor = vec4(cube.xyz, 1.0);
}

Answer 1

The problem is your function CreateARGBBitmapContext the line

var context = new CGBitmapContext (bitmapData, pixelsWide, pixelsHigh, 8, bitmapBytesPerRow, colorSpace, CGImageAlphaInfo.PremultipliedFirst);

If you change

CGImageAlphaInfo.PremultipliedFirst 

to

CGImageAlphaInfo.PremultipliedLast 

that should fix your code.